,transcriber's ,notes3 ,underscores 80 before and after a word or phrase indicate italics in the original text4 ,a single underscore indicates a subscript4 ,equal signs 80 before and after a word or phrase indicate bold in the original text4 ,carat symbol 80 designates a superscript4 ,small capitals have been converted to ,,solid capitals4 ,old or antiquated spellings have been preserved4 ,typographical errors have been silently corrected but other variations in spelling and punctuation remain unaltered4 ,the two advertisements at the beginning of the book have been moved to the advertisement section at the end4 ,,sewage ,,disposal ,,works ,,their ,,design ,,and ,,construction ,,by ,w4 ,c4 ,,easdale1 ,m4,s4,e4 ,m4,r4,,san4,i4 ,,author ,,of 8,,the ,,practical ,,management ,,of ,,sewage ,,disposal ,,works0 #aee ,,illustrations ,illustration ,london3 ,e4 ,f4 ,n4 ,,spon1 ,,limited1 #eg ,,haymarket ,new ,york3 ,,spon ,,chamberlain1 #abc ,,liberty ,,street #aiaj ,,preface ,in the course of the preparation of a series of articles for 8,surveying and the ,civil ,engineer10 dealing with the numerous and varied types of appliances used in connection with ,sewage ,disposal ,works1 it occurred to the ,author that it might be useful to many ,engineers1 and especially to ,students1 to have the whole series published in a permanent form for reference4 ,at the same time1 it appeared to afford an excellent opportunity to include full details of all the various methods of design and construction in general use1 and thus provide a complete work dealing with the whole subject4 ,the result is the present volume1 which1 it is hoped1 will prove of value to those engaged in this branch of engineering4 ,in any future editions that may be required1 it will be the endeavour of the ,author to omit any details which may have become obsolete1 and to include particulars of any new methods of construction1 systems or appliances1 which may be brought into use from time to time1 and he will therefore be glad to receive particulars of new appliances and systems as they are introduced4 ,w4 ,c4 ,,easdale4 #bh ,,victoria ,,street1 ,,westminster1 ,s4,w4 #aiaj4 ,,contents ,,page ,,introduction #a ,,screens3 ,simple--,rotary--,for deep sewers--,mechanical--,other types #c ,,storm-,,water ,,overflows3 ,diverting plate--,fixed weirs--,movable weirs #af ,,detritus ,,tanks3 ,capacity--,dortmund type--,apparatus for sludge removal #bc ,,tanks3 ,various types--,capacities--,general construction details--,flow through tanks--,sludge well--,roofs--,inlets and outlets--,precipitation tanks--,dortmund types--,hydrolytic tank--,imhof tank--,skegness tank--,candy-,whittaker tank--,non-septic cylinder--8,kessel0--,separator--,fieldh ouse tank--,dibdin slate beds #bi ,,sludge ,,disposal3 ,sludge removal--,apparatus--,chemical mixers--,sewage mixers--,sludge presses--,hydro-extractor for sludge--,sludge draining beds #ga ,,percolating ,,filters3 ,general design--,various types of construction--,floors of filters-- ,sub-drainage--,floor-tiles--,walls of filters--,planning of filters--,filtering material--,grading of material --,methods of distribution--,appliances for distribution --,automatic revolving distributors--,power-driven revolving distributors--,automatic travelling distributors--,power-driven travelling distributors--,fixed distributors--,troughs--,spray-nozzles-- ,methods of feeding percolating filters--,continuous versus intermittent supply--,supply channels and pipes-,dosing apparatus #he ,,effluent ,,settling ,,tanks ,,or ,,humus ,,pits #ahb ,,sand ,,filters #ahe ,,contact ,,beds3 ,causes of failure--,general principles of design--,general construction--,methods of distribution --,sub-drainage--,material for filling contact beds --,automatic apparatus #ahi ,,capacity ,,of ,,percolating ,,filters ,,and ,,contact ,,beds3 ,relative capacities--,table of requirements #bbb ,,storm-,,water ,,treatment3 ,stand-by tanks--,methods of construction and operation #bbg ,,measuring ,,apparatus #bcb ,,sterilisation ,,of ,,sewage ,,effluents3 ,purpose and practicability--,apparatus for manufacture of hypochlorite solutions--,appliance for injection of chemicals #bdj ,,index #bea ,,sewage ,,disposal ,,works ,,their ,,design ,,and ,,construction ,,introduction4 ,in approaching a subject upon which so much has already been written1 it may be desirable to point out that the improvements which have taken place in recent years in connection with sewage disposal are so extensive and varied1 and have developed at such a comparatively rapid rate1 that most treatises now in existence are in many respects more or less out of date4 ,it is true that further developments may be anticipated in the future1 but these will probably be concerned more with additions and improvements in matters of detail than of principles1 which are now to a great extent agreed upon4 ,the time would thus appear to have arrived when it is desirable to describe in detail the various methods of construction now generally adopted in the design1 of present-day sewage disposal works4 ,in order to avoid a repetition of the usual preliminary details to be found in all the existing literature devoted to this subject1 it is assumed that readers are acquainted with the nature of the problem to be solved in the design of sewage disposal works1 with the varying characteristics of the different liquids included under the term 8sewage10 and with the engineering formul and requirements involved in the design of tanks1 filters1 and similar constructional works4 ,the present volume will thus consist exclusively of descriptions1 illustrated with drawings and photographs1 of the various tanks1 chambers1 filters1 beds1 and other details of sewage works1 including the numerous types of appliances required in connection therewith4 ,in other works dealing with this subject it has been customary to use as illustrations1 drawings of works actually carried out by their authors or other engineers4 ,while these are interesting and valuable to a certain extent1 their application under other conditions is limited1 and their usefulness is thus much reduced4 ,in the present volume the illustrations of the various details of construction do not1 as a rule1 represent actual working drawings adapted to any particular set of conditions1 but are shown in diagrammatic form for the purpose of serving as suggestions to engineers in search of ideas which they can adapt to meet the requirements of any particular scheme upon which they may be engaged4 ,it will follow that the engineer must in all cases rely upon his own practical experience and judgment in deciding to adopt any of the various methods of design and construction illustrated and described in the following pages2 and it may be found that a combination of several types1 or even a combination of several details of different types1 combined with practical experience and mature judgment1 will frequently produce the most suitable and efficient scheme4 ,,screens4 ,on arrival at the disposal works1 the first stage of the process through which the sewage passes is generally that of screening for the purpose of arresting the grosser solids in suspension4 ,in a number of cases where the sewage is delivered by gravitation1 there are no screens of any kind in use1 reliance being placed upon the detritus chambers to perform the duty of arresting the floating solids1 as well as the grit and other mineral matters1 of such a specific gravity that they are readily deposited by simply reducing the velocity of the flow4 ,where the levels involve the use of pumping plant1 screens are a necessity1 and1 as the ,royal ,commission on ,sewage ,disposal have expressed the opinion that all sewage should be screened1 it will apparently be necessary to provide screens in all future schemes4 ,illustration3 ,,fig4 #a4--,,simple ,,screen4 ,simple ,screens4--,the simplest type of screen is in the form of a grating1 consisting of vertical iron bars in a stout iron frame1 arranged to fit into grooves cut in the side walls of the screen-chamber1 or in channel-iron guides attached to the sides of the chamber4 ,as a general rule the vertical bars are round in section1 but some engineers prefer to use flat bars with their longer side parallel to the line of flow1 while others even go so far as to use wedge-shaped bars with the thick end facing the flow of sewage4 ,in the latter case1 the idea is to facilitate the passage through the screen of those matters which are too small to be arrested on the front of the bars1 but large enough to be caught between the bars1 and thus possibly choke the intervening spaces4 ,as all simple fixed screens must of necessity be cleaned by hand1 they are usually arranged at an angle of about #fj degrees to the floor of the chamber1 in order that the matters arrested may be more easily drawn up by a hand rake to the top of the screen4 ,fig4 #a shows a screen of this type in plan and section1 with a large scale detail of the round1 flat and wedge-shaped bars previously described4 ,it will be noticed that a narrow platform of boards is shown across the chamber1 at the top of the screen1 to receive the screenings1 which are then thrown into a barrow for removal to their final destination4 ,one important point to be remembered in the design of the chamber for screens of this type is1 that the bottom of the screen should be placed in a sump some #ab inches or so below the invert of the incoming sewer1 so as to provide space for the accumulation of a certain amount of sludge and screenings without choking the screen4 ,this sump should be provided with a washout valve4 ,it is advisable to have all screen-chambers in duplicate1 so that one of them may be in use while the other is being cleaned4 ,the spaces between the bars vary in width with the character of the sewage1 but the distance most generally adopted is half an inch4 ,the important point to be considered is1 that while the screen should arrest all the larger suspended matters it is intended to intercept1 it should allow a free passage to all others without becoming rapidly choked4 ,another important factor in the efficiency of a fixed screen is its width4 ,the greater the width1 the less will be the liability to choke1 and consequently it will not require raking so frequently to keep it in proper order4 ,rotary ,screens4--,where the flow of sewage is sufficient for the purpose1 and it is desired to reduce the necessary attention to the minimum1 the self-cleansing rotary screen1 manufactured by ,messrs4 ,john ,smith and ,co41 may be adopted4 ,this is illustrated in ,fig4 #b1 from which it will be seen that it consists of a revolving wire screen1 extended between two rollers1 one below and the other above the sewage level4 ,the upper roller is rotated by means of a water wheel driven by the sewage4 ,a rotary brush is fitted to the shaft and driven in the opposite direction to the screen roller1 so that it brushes off the screenings into a trough1 from which they are removed by hand4 ,illustration3 ,,fig4 #b4--,,rotary ,,screen4 ,screens for ,deep ,sewers4--,in cases where the depth of the sewer makes it inconvenient to adopt a fixed screen1 the double lifting screen1 manufactured by ,messrs4 ,adams ,hydraulics ,ltd41 may be used1 as shown in ,fig4 #c4 ,this consists of duplicate screens1 arranged to slide up and down in cast-iron guides attached to the walls of the chamber4 ,these screens are raised and lowered by a chain1 which passes over a drum revolved by hand4 ,the main screen is in the form of a basket1 with a hinged front1 which falls to the floor of the chamber when this screen is lowered into position4 ,when it is desired to clean out this basket screen1 the other plain guard screen is lowered into position in front of the basket-screen1 and the latter is then raised4 ,as the chain by which the basket-screen is raised is attached to the top of the hinged front1 the action of raising this screen first draws up the hinged front and this prevents the screenings falling out4 ,after this screen has been emptied1 it is again lowered into position1 and the guard-screen raised to permit the sewage to flow direct into the basket-screen4 ,illustration3 ,,fig4 #c4--;,,double ,,lifting ,,screen4 ,illustration3 ,,fig4 #d4--,,mechanical ,,screen4 ,illustration3 ,,fig4 #e4--,,mechanical ,,screen4 ,illustration3 ,,fig4 #f4--,,mechanical ,,screen4 ,mechanical ,screens4--,in larger schemes1 where power is available for the purpose1 mechanically operated screens are frequently adopted1 as they are not only self-cleansing but the screenings are delivered automatically at or above the ground level1 and thus very little labour is involved in removing these matters4 ,figures #d1 #e1 #f1 #g illustrate four examples of this type of screen1 manufactured respectively by ,messrs4 ,ham1 ,baker and ,co41 ,ltd41 ,messrs4 ,j4 ,blakeborough and ,son1 ,ltd41 ,messrs4 ,s4 ,s4 ,stott and ,co41 and ,messrs4 ,j4 ,wolstenholme and ,co4 ,the general features of these screens are an inclined screen or strainer1 fixed in the channel or catchpit through which the sewage flows to the tanks or to the pumps1 and a raking apparatus with special shaped prongs1 which travel in the spaces between the bars forming the screen and remove the refuse4 ,the ,stott screen includes a rake cleaning gear1 consisting of a revolving steel comb1 by means of which the screenings are removed from the prongs of the rake while they are in motion4 ,illustration3 ,,fig4 #f;,a4--,,rake ,,cleaning ,,gear ,,for ,,fig4 #f4 ,illustration3 ,,fig4 #g4--,,mechanical ,,screen4 ,in the case of the screen1 manufactured by ,messrs4 ,whitehead and ,poole1 illustrated in ,fig4 #h1 the bars are of tapered steel1 and are so arranged that they can be removed and replaced if necessary4 ,the special friction drive with which this machine is fitted1 prevents the breaking of the chain should the rake prongs become caught in the screen4 ,the rake-cleaning gear consists of two swing levers1 which carry a cleaning comb and a balance weight to hold it in position over the dirt tray4 ,as the rakes bring up the screenings and reach the delivery position1 they pass through the cleaning comb1 which is1 at the same time1 forced down by a catch on the chain engaging with flanged rollers on the end of the swing levers4 ,in this way the rakes are effectively cleaned1 and it is impossible for the rake prongs and the comb to foul each other4 ,in addition to the screens already described1 mention may be made of the special drum-shaped screen invented by ,mr4 ,baldwin ,latham and the numerous types of mechanically-operated screens in use in ,germany1 all more or less elaborate in character4 ,further details of these are probably unnecessary1 as the aim of the engineer engaged in the design of sewage disposal works should be to adopt those appliances which are of the simplest possible form consistent with the requirements of the case with which he is called upon to deal4 ,some engineers prefer to use screens specially designed by themselves to meet the requirements of each particular scheme1 and while this method provides scope for the exercise of a considerable amount of ingenuity1 it is liable to involve greater expense than would be incurred by the adoption and possible adaptation of one of the various types already on the market4 ,illustration3 ,,fig4 #h4--,,mechanical ,,screen ,,with ,,rake ,,cleaning ,,gear4 ,,storm-,,water ,,overflow ,,weirs4 ,the proper design of weirs for diverting the excess volume of sewage in times of storm has not in the past always received sufficient consideration4 ,too frequently it has been dealt with by rule of thumb4 ,in the first place the position for the weir has not always been well chosen2 but1 as a result of the recommendations of the ,royal ,commission on ,sewage ,disposal1 it will be necessary in the future to construct these weirs1 in all cases which require the approval of the ,local ,government ,board1 after the screen4 ,this is a wise precaution1 as it prevents the possibility of a storm-water overflow coming into action as a result of want of attention to the screen4 ,in this position the factor which has the greatest influence upon the proper working of such weirs is the rate of flow into the detritus tanks1 i4e4 the area of the inlets to these tanks4 ,it is true that these may be regulated by the use of valves1 but unless these valves1 when once adjusted to the correct height1 can be permanently locked in that position1 it leaves them at the mercy of an unscrupulous workman1 who may1 if he wishes1 close them entirely1 and thus cause the entire flow of sewage to pass over the storm overflow weir in order to save himself the trouble of attending to the tanks and filters4 ,it is probably with the intention of preventing the possibility of such mismanagement that the ,local ,government ,board object to valves on the inlets to the detritus tanks4 ,one method of preventing trouble is to use simple hand-stops1 and provide the frames in both inlets but only one door1 so that it is impossible for the man to close both inlets at the same time4 ,the ,local ,government ,board are also usually averse to the use of any type of movable weir1 and prefer the simple fixed weir4 ,diverting ,plate4--,many ingenious devices have been adopted in the past for the purpose of ensuring the diversion of all the excess volume above a certain fixed quantity4 ,one of these is shown in ,fig4 #i1 where it is assumed that all in excess of the volume which is taken by the sewer flowing four-fifths full is to be discharged over the overflow4 ,in order to facilitate this result1 an iron plate is fixed at the level of the weir 7say four-fifths of the diameter of the sewer71 over the whole of the outlet end of the chamber or man-hole1 with a sharp edge on the side facing the flow1 so that when the sewage in the chamber rises above this level1 the excess volume above that flowing at a depth of four-fifths of the diameter of the sewer1 is automatically diverted by the plate and caused to pass away over the weir4 ,the invert of the chamber must naturally correspond with the diameter of the sewer4 ,illustration3 ,,fig4 #i4 ,fixed ,weirs4--,even this ingenious method of diversion is1 however1 not accurate1 as no provision is made to counteract the effect of the increased head on the outlet from the chamber1 due to the backing up of the sewage in passing over the weir4 ,where a fixed weir is alone permissible1 the only really satisfactory method of securing the desired result1 is to increase the width of the overflow weir to such an extent that the maximum depth of storm-water1 which may possibly flow over the weir1 is reduced to the minimum1 say one inch1 and thus the effect of this head on the normal outlet from this chamber 7i4e4 on the inlet to the detritus or sedimentation tanks7 is also reduced to the minimum4 ,this will necessitate careful consideration1 and a special set of calculations in each case4 ,where it is found that the execution of the above suggestion involves the construction of a weir of abnormal and unpractical width1 it will be found convenient to arrange the normal dry-weather outlet from this chamber in the form of a narrow vertical slot1 which can be most easily provided in a simple door or stop in a grooved frame1 fixed in the outlet from this chamber4 ,fig4 #aj shows an example of this slotted door1 and when the correct width of the slot has been ascertained by actual experiment1 the door should be bolted to the frame1 so that it cannot be removed or altered by any unauthorised person4 ,from the drawing it will be seen that it is not difficult to calculate the dimensions of the slot orifice1 so that with the head due to the height of the storm overflow weir it shall discharge the desired volume 7say three times the dry-weather flow71 and if the width of the overflow weir is then calculated to take the excess volume with a depth of one inch of water over the weir1 this extra one inch of head will have very little effect on the discharge through the slot outlet4 ,illustration3 ,,fig4 #aj4 ,illustration3 ,,fig4 #aa4--;,,floating ,,weir4 ,illustration3 ,,fig4 #ab4--,,swinging ,,siphon4 ,movable ,weirs4--,if1 however1 it is desired to provide for an absolutely correct diversion of the storm-water1 this can only be done by the use of a movable weir4 ,there are two types of this form of weir on the market at present1 both manufactured by ,messrs4 ,adams ,hydraulics1 ,ltd4 ,fig4 #aa shows a floating weir1 circular in form1 arranged by means of floats to rise and fall freely with the level of the sewage in the chamber4 ,the joint between the fixed and moving portions of the apparatus consists of an air-lock1 and is thus frictionless4 ,the floats are adjusted to bring the lip of the weir at such a depth below the top water level1 that the volume which can pass over the weir without raising it is the maximum volume which it is desired to pass to the tanks and filters4 ,as soon as the flow of sewage exceeds this volume1 it naturally causes the floats to raise the lip of the weir1 and in this way the volume passing to the tanks and filters can never exceed the predetermined fixed volume1 and all in excess must pass over the overflow weir4 ,fig4 #ab shows a swinging syphon1 which has the same effect as the floating weir4 ,in this case the syphon has both legs trapped1 so that it acts as a continuous syphon1 and it is pivoted on the top of the division wall to swing freely4 ,to the inlet leg1 on the sewer side of the division wall1 is attached an adjustable float1 of sufficient buoyancy to raise this leg of the syphon 7and with it the outlet leg as well7 as the sewage rises in the chamber4 ,it will be seen that the difference in level between the lip of the inlet leg and the buoyancy point of the float1 represents the head which controls the maximum rate of flow through the syphon1 and that immediately this is exceeded the float rises1 and with it the syphon leg1 so that all the excess volume of sewage1 above the fixed maximum rate of flow through the syphon1 must of necessity pass over the storm-water overflow weir4 ,,detritus ,,tanks ,,or ,,grit ,,chambers4 ,the function of these tanks is to arrest all mineral matter1 such as stones1 sand1 road-grit1 and similar substances which cannot be decomposed in the subsequent stages of treatment1 and would thus choke the tanks and filters4 ,the essential factor in their operation is a reduction of the rate of flow of the sewage1 so that all matters of a greater specific gravity than the water and the organic matters in suspension may be deposited by subsidence4 ,at the same time the velocity should not be reduced to such an extent as to allow the organic matters in suspension to settle out1 as these can be more suitably dealt with in the subsequent tanks provided for that purpose4 ,from this it will be seen that considerable care is needed in designing these tanks if they are to have the desired effect4 ,further1 it is very essential that every facility shall be provided for removing the matters which are deposited with as little trouble as possible4 ,capacity of ,detritus ,tanks4--,too frequently there is very little evidence of design in these tanks1 especially in the provision of suitable sludge outlets4 ,before all1 there should be at least two detritus tanks in every case1 so that one may remain in work while the other is being cleaned out1 and1 if the recommendations of the ,royal ,commission on ,sewage ,disposal are followed1 each should have a capacity of not less than one-hundredth of the daily dry-weather flow4 ,a simple form of detritus tank is shown in ,fig4 #ac4 ,the essential features are1 a floor with a sharp fall towards the inlet end of the tank and a sludge outlet at its lowest point4 ,in this case a sludge plug valve is shown4 ,this is suitable for all cases where the sludge can be discharged to the sludge bed by gravitation4 ,where the levels do not permit of this1 and it becomes necessary to raise the sludge1 a chain-pump may be fixed in the detritus tank itself4 ,as1 however1 this would involve a separate chain-pump for each detritus tank1 as well as for each of the other subsequent tanks1 it is usually found more convenient in such cases to construct a separate sludge-well provided with a chain-pump1 and arranged at such a depth that the sludge from all the tanks will reach it by gravitation4 ,this arrangement will be shown later in connection with the sedimentation tanks4 ,the inlets to detritus tanks must be provided with valves1 so that the flow of sewage may be shut off when it becomes necessary to empty the tanks4 ,in order to prevent any misuse of these valves either in error1 or wilfully1 by closing both simultaneously and thus causing the whole of the sewage to pass over the storm-water overflow weir1 the inlet valves should consist of grooved frames with one interchangeable door4 ,by this means it is impossible for anyone to close both inlets at the same time4 ,illustration3 ,,fig4 #ac4--;,,detritus ,,tanks4 ,illustration3 ,,fig4 #ad4 ,dortmund ,type of ,tank4--,where the volume of sewage is fairly large1 and it would be convenient to have the sludge outlet at #b feet to #c feet below the level of the invert of the outfall sewer1 the advantages of designing the detritus tanks on the lines of the ,dortmund tank may be considered4 ,an example of this kind of tank is shown in ,fig4 #ad4 ,tanks of this type have the following special features3--,great depth--from #af feet to #bj feet below water level--and the bottom in the form of an inverted cone1 with an outlet at its apex connected to a cast-iron sludge delivery-pipe1 which may be carried up either outside the tank1 as shown in solid lines1 or on the inside of the tank1 as shown in dotted lines4 ,in either case this pipe should be continued vertically up to1 and finish with1 an open end at the level of the top of the wall of the tank1 so as to form a means for inspection and rodding in case the pipe should become choked4 ,from this vertical pipe a right-angled branch is arranged at about #b feet below the top-water level in the tank1 and provided with a sluice-valve4 ,ordinarily this valve is closed4 ,when it is desired to remove the sludge deposited in the cone-shaped bottom of the tank1 the sluice-valve on the sludge outlet is opened and the sludge is forced up by the head of water1 due to the difference in level between the top-water level in the tank and the invert of the sludge-outlet4 ,it has been stated that this method of sludge removal is subject to difficulties1 due to the consolidation of the sludge in the cone1 to such an extent that it becomes of too thick a consistence to flow up the vertical pipe4 ,in some cases a special mechanical contrivance is adopted1 by means of which the sludge may be stirred up at the apex of the cone-shaped bottom while the sludge-valve is open4 ,again1 in a special form of tank which has been brought into use in ,germany1 the sludge is stirred up by means of jets of water1 under pressure from the main1 forced through a ring-shaped perforated pipe laid near the apex of the cone4 ,in both cases it is evidently assumed that the sludge will only be removed at long intervals1 and in the author's opinion the difficulties referred to above may be avoided by the application of the motto 8,little and often10 as described in his book on the management of ,sewage ,disposal ,works4 ,illustration3 ,,fig4 #ae4--,,sludge ,,scraper ,,in ,,detritus ,,tank4 ,special ,apparatus for ,sludge ,removal4--,a further type of detritus tank is illustrated in ,fig4 #ae1 in which the tank is circular in form but has a flat bottom4 ,the sludge is discharged by the same means as that shown in ,fig4 #ad1 but a special scraping machine operated by hand is used to facilitate the removal of the sludge by drawing it towards the inlet to the sludge pipe1 which is situated at the centre of the floor4 ,the scraper1 which is manufactured by ,messrs4 ,ham1 ,baker and ,co41 is helical in form1 and is attached to and rigidly supported by a framework mounted on the central shaft1 which is rotated by suitable gearing fixed at the side of the tank over the sludge discharge inspection chamber1 so that the operator may be able to regulate the rate of the sludge delivery4 ,it will be noticed that the outlet from this tank is by means of cross-channels1 described in detail later in connection with sedimentation tanks4 ,,tanks4 ,under this heading are included a large number of tanks of various types and systems1 for each of which some particular advantage is claimed in ordinary circumstances1 or some peculiar suitability for special conditions4 ,all are1 however1 ostensibly designed for the purpose of arresting the organic matters in suspension1 in order to prepare the sewage for the subsequent stage of oxidation in contact beds1 on percolating filters or on land4 ,types and ,capacities of ,ordinary ,tanks4--,in addition to detritus tanks described in the preceding chapter1 the ,royal ,commission on ,sewage ,disposal1 in its fifth ,report1 has dealt with five different methods of tank treatment in detail4 ,these are3-- #a4 ,septic tanks1 having a total capacity of about #bd hours' dry-weather flow4 #b4 ,continuous-flow settlement tanks without chemicals1 having a total capacity of about #ae hours' dry-weather flow4 #c4 ,continuous-flow settlement tanks with chemicals1 having a total capacity of about #h hours' dry-weather flow4 #d4 ,quiescent settlement tanks without chemicals4 #e4 ,quiescent settlement tanks with chemicals4 ,the two last-mentioned have each a total capacity of about #bd hours' dry-weather flow4 ,illustration3 ,,fig4 #af4 ,illustration3 ,,fig4 #af4 ,in all these five types of tanks the method of construction is very similar1 generally rectangular in plan and of a moderate depth4 ,as a rule they are connected by means of a supply channel to the preceding detritus tanks1 and the total capacity is divided up into a number of units varying with the size of the scheme4 ,the ,royal ,commission suggest the following divisions3-- #a4 ,septic tanks3 #e tanks1 with an additional spare tank4 #b4 ,continuous-flow settlement without chemicals3 #f tanks1 with #b additional spare tanks4 #c4 ,continuous-flow settlement with chemicals3 #f tanks1 with #b additional spare tanks4 #d4 ,quiescent-settlement without chemicals3 #h tanks1 with #b additional spare tanks4 #e4 ,quiescent settlement with chemicals3 #h tanks1 with #b additional spare tanks4 ,the general features of construction are3-- ,substantial walls in brickwork1 concrete1 plain or reinforced1 and of a suitable thickness to withstand with safety the pressures they are required to resist2 sloping floors provided with suitable outlets for both liquid and solid contents at the bottom1 and specially arranged inlets and outlets at the top4 ,in connection with the floors1 sufficient care has not always been devoted in the past to the consideration of the most convenient method to adopt1 in view of the necessity of removing the sludge4 ,in some cases1 the floors have been laid with a slope towards the outlet end1 and1 as the greatest accumulation of deposit takes place at the inlet end1 great difficulties have been experienced in removing the sludge4 ,there is very little doubt that if suitable arrangements are made1 by means of which the accumulation of solids deposited at the inlet ends of tanks can be removed without drawing off the total contents of the tank1 much labour will be saved4 ,with this end in view1 the design illustrated in ,fig4 #af is suggested as a model which may be adopted exactly as shown1 or1 with some modifications1 adapted to meet the special requirements of particular cases4 ,it will be noticed that a submerged weir wall is introduced at some distance 7which will vary with the method upon which the tank is operated and with the character of the sewage7 from the inlet end of the tank1 so as to retain the larger portion of the solids in this separate compartment4 ,the floor of this section is laid with a comparatively steep gradient leading to the sludge outlet4 ,a separate outlet1 fitted with a floating arm1 may be provided for drawing off the top water down to the level of the top of the weir wall4 ,below this level1 in ordinary circumstances1 only the contents of the separate compartment at the inlet end of the tank will be drawn off in removing the sludge4 ,a valve is provided at the bottom of the weir wall1 so that the entire contents of the tank may be drawn off should it be found necessary at long intervals4 ,an alternative to the submerged weir wall is shown in ,fig4 #ag1 in the form of a division wall carried up to the top of the tank1 with orifices below the top water level through which the sewage passes when the tank is in use4 ,these apertures are provided with valves1 so that they may be closed when the solids in the compartment at the inlet end of the tank are drawn off1 and thus obviate the necessity for emptying the whole of the tank4 ,illustration3 ,,fig4 #ag4 ,from observations which have been made in various places1 it has been found that although the actual capacity of the tanks corresponded to anything from #ab up to #bd hours of the daily dry weather flow1 the period during which the sewage remained in the tank1 or rather the time taken for the sewage to pass through the tank1 was much less than it was anticipated would be the case4 ,in one instance1 it was noticed that the sewage passed through a tank of a capacity equal to #ae hours' dry weather flow in #d hours1 and1 although it is obvious that the same efficiency of sedimentation could not be secured by passing the sewage at the same rate through a tank of a capacity of #d hours' flow1 it would seem that the full effect of the larger tank was not brought into play4 ,a possible explanation is that the form of the tank and the arrangement of the inlet and outlet were such that the flow of sewage through the tank was more or less in a direct line from the inlet to the outlet1 and this1 if correct1 would lead to the conclusion that there is room for improvement in the design of the tank1 in order to cause the sewage in its passage to be spread out over the whole area of the tank4 ,with this end in view the author has specially designed the arrangement illustrated1 ,fig4 #ah1 as a suitable method of preventing the sewage passing direct from the inlet to the outlet4 ,it will be noticed that the sewage enters the first compartment about #c feet below the top water level1 and by means of three cross walls is made to flow down to within a short distance of the floor in one compartment1 and up to within a short distance of the top water level in the next1 and that this occurs twice in the total length of the tank4 ,by sloping the floor from the centre both ways1 i4e4 to the inlet and outlet ends1 and providing sludge outlets at the lowest points in each case1 every facility is made for removing the deposit and for emptying each half of the tank whenever it may be found necessary4 ,further1 by arranging the sludge outlets in pockets or sumps1 situated below the level of the lowest point of the floor itself1 it is possible to draw off the sludge in small quantities at frequent intervals without emptying the tank itself4 ,the chief factors in causing the sewage to be uniformly spread out over the whole area of the tank are1 however1 the valves or penstocks on the inlet and outlet pipes1 and on the pipes in the central cross wall4 ,by suitable adjustment of these penstocks1 partially closing those through which the sewage has a tendency to flow most freely and opening the others1 there should be no difficulty in securing a uniform distribution of the sewage4 ,in any case the actual direction of the flow of the sewage is1 by means of these penstocks1 entirely under control4 ,the inlets to the tank being submerged below the water level in the supply channel1 will secure a more uniform rate of flow through all the inlet pipes than if they were placed at the top water level1 and the valves on these pipes provide facilities for any further regulation that may be required4 ,the most important point to be observed1 however1 is that the rate of flow from the outlets of the tank should be uniform4 ,in order that this may be secured1 these pipes are submerged on the inside of the tank1 but have their outlets set at the top water level1 so that the actual discharge may be visible1 and thus render it possible to regulate the rate of flow from each pipe by means of the penstocks provided for the purpose4 ,further1 the openings in the middle cross wall may be adjusted to control the direction of the flow through the tank by means of the penstocks1 which also serve to shut off either half of the tank when the other is emptied4 ,illustration3 ,,fig4 #ah4 ,illustration3 ,,fig4 #ah4 ,illustration3 ,,fig4 #ai4 ,another method of ensuring uniformity of flow over the whole area of a tank1 is to arrange it in the form of a wedge1 with the inlet at the narrow end and the outlet in the form of a weir at the wide end4 ,this form of tank is shown1 ,fig4 #acd1 page #ahc1 for settling out the humus in filter effluents4 ,the same tank1 with a greater depth1 would be equally suitable as an ordinary sedimentation tank for sewage1 and several could be arranged in such a way that three or four would form a half-circle1 i4e4 the angle between the two side walls of each tank would be #fj degrees or #de degrees4 ,the principles embodied in the preceding suggestions can be applied to most types of rectangular tanks4 ,sludge ,well4--,in connection with the actual method of conducting the sludge from these tanks to the sludge disposal area1 the remarks made under the heading of detritus tanks will apply4 ,a convenient arrangement for a sludge well1 where a number of tanks are involved1 is shown in ,fig4 #ai1 which is self explanatory4 ,for small schemes a chain-pump operated by hand may be used to raise the sludge from the well4 ,in larger schemes where power is available1 sludge elevators of the bucket type1 as shown in ,figs4 #bj1 #ba and #ba;,a1 are very convenient4 ,roofs over ,tanks4--,with regard to the question of roofs over tanks1 it is now generally admitted that these have very little1 if any1 effect upon the working of the tank1 and they may therefore be dismissed in a few words4 ,under certain circumstances it may be desirable for sentimental reasons to cover sewage tanks1 and in such cases the general practice is to form concrete arches covered with earth and sown with grass4 ,reinforced concrete construction may sometimes be found very suitable1 while1 in other cases1 galvanized corrugated-iron roofs1 supported on an iron framework carried on the walls of the tanks1 are preferred4 ,in very small installations1 #a-;inch or #b-;inch creosoted deal boards1 laid loose1 but fitting close together with their ends supported in a rebate in the top of the wall1 make a very good cover1 as they are easily removed whenever it becomes necessary to inspect or gain access to the tank4 ,illustration3 ,,fig4 #bj4--,,sludge ,,elevator4 ,details of ,inlets and ,outlets4--,among the most important points to be considered in designing sewage tanks is the arrangement of the inlets and outlets1 as upon these depends to a very great extent the efficiency of the process4 ,in order to afford a means of selecting the most suitable arrangement for any particular case a number of different methods are illustrated4 ,illustration3 ,,fig4 #ba4--,,sludge ,,elevator4 ,illustration3 ,,fig4 #ba;,a4--,,sludge ,,elevator4 ,fig4 #bb shows the simplest form of trapped inlet and outlet1 consisting of cast-iron ,tee junction pipes1 the junction being built into the wall of the tank and fitted with a valve or penstock4 ,the lower end of the trapped pipe is generally about #c feet below the top water level1 but in special cases may be much deeper4 ,the upper end of this pipe terminates at some distance 7e4g4 about twice the diameter of the inlet junction7 above the top water level1 and the top is left open or fitted with a blank flange for purposes of inspection4 ,where a roof is provided over the tank1 it is desirable to continue this pipe up and through the roof1 so that it may still be available for inspection4 ,in large tanks1 or any tanks having a width of more than #f feet1 several of these inlet and outlet pipes should be provided1 one for about every #f feet of width1 in order to spread the sewage as much as possible over the whole area of the tank4 ,a valve should be provided on the inlet pipe4 ,this is essential in order that the flow of sewage to the tank may be shut off whenever it needs attention or has to be emptied4 ,where there are several tanks with their outlets discharging into a common channel1 it will be found desirable to have valves on the outlets as well as on the inlets4 ,a slight fall should always be allowed from the invert of the inlet to the invert of the outlet pipe1 and again from the latter to the tank effluent channel or pipe leading to the filters4 ,illustration3 ,,fig4 #bb4 ,illustration3 ,,fig4 #bc4 ,illustration3 ,,fig4 #bd4 ,in ,fig4 #bc a somewhat similar arrangement is shown1 but instead of ,tee junctions the inlets and outlets are formed of easy bends1 which may be in cast-iron or glazed stone ware as indicated4 ,the observations made above in connection with ,fig4 #bb apply generally to ,fig4 #bc4 ,fig4 #bd is a plan of ,fig4 #bc1 to show a number of inlets and outlets to one tank4 ,in ,fig4 #be the trapped inlet and outlet is formed by means of a cross wall carried up to the top of the tank with openings at the floor level in the form of arches4 ,it is considered by some engineers that this method is a more substantial form of construction1 and that it assists to a great extent in spreading the flow of the sewage over the whole area of the tank4 ,in ,fig4 #bf both the inlet and outlet is in the form of a weir1 running the full width of the tank1 and it is probable that this is the most efficient means of ensuring that the flow of sewage shall spread over the whole area of the tank4 ,the trapping of the inlet and outlet in this case is obtained by the use of scum boards or plates1 as shown4 ,when more than one tank of this type is required1 it becomes necessary to provide a separate feed channel or carrier in addition to the channel immediately in front of the inlet weir1 in order to arrange means for shutting one or more tanks out of work when required4 ,illustration3 ,,fig4 #be4 ,the method of arranging the inlets and outlets shown in ,fig4 #bg1 consists of constructing extra deep sewage carriers and tank effluent channels1 and making the connections from these to the tank at the desired depth below the top water level in the tank4 ,it is true that these deep channels always stand full of sewage or tank effluent while the tank is in operation1 but it is assumed that the passage into the tank of all solid matters in suspension is facilitated1 especially during the minimum flow of sewage4 ,it is essential that both channels should be well dished towards the tank on either side1 so as to avoid all corners where solids may lodge1 and render it easy to clean out the channels when the tank is emptied4 ,illustration3 ,,fig4 #bf4 ,illustration3 ,,fig4 #bg4 ,illustration3 ,,fig4 #bh4 ,illustration3 ,,fig4 #bi4--,,type ,,of ,,floating ,,arm4 ,the various types of inlets and outlets described above are more particularly suitable for tanks which come under the terms 8septic0 and 8continuous-flow sedimentation without chemicals40 ,it is not necessary that the inlets and outlets should both be of the same type4 ,various combinations may be adopted1 according to the requirements of each case and the judgment of the engineer4 ,similar methods may be utilised for 8continuous-flow sedimentation tanks with chemicals10 but they need the addition of floating arms for the purpose of drawing off the top water before the sludge is removed4 ,the type of inlet and outlet more generally in use for chemical precipitation processes is shown in ,fig4 #bh1 as in these cases there is no need to preserve a scum on the surface4 ,the connection between the sewage carrier and the tank is usually in the form of a sluice gate1 and simple wooden boxes are provided round the inlet and outlet in order to divert the flow towards the bottom of the tank4 ,it is also found desirable in some cases to provide scum-boards for the purpose of arresting the grease1 which naturally rises to the surface1 and must not be allowed to pass away with the effluent4 ,the floating arm outlet is essential1 particularly for tanks which are designed for 8quiescent sedimentation with or without chemicals10 and the usual form of outlet into a channel a few inches only below the inlet level is not needed1 as tanks of this type are filled and allowed to stand full for a certain period1 and the contents are then drawn off through the floating arm4 ,the function of this appliance is to draw off the whole of the clear liquid contents1 from a point a few inches below the surface1 at a slow rate1 and without disturbing the sludge at the bottom4 ,illustration3 ,,fig4 #cj4--;,,decanting ,,valve4 ,a type of floating arm is shown in detail in ,fig4 #bi4 ,in order to prevent any possibility of these arms drawing off sludge by an oversight1 when approaching the floor of the tank1 the chain attached to the float should be arranged to check the fall of the arm at a point which will be above the level of the sludge1 or1 if there is any possibility of the chain being tampered with by unauthorised persons1 the fall of the arm may be arrested with certainty by means of a bracket1 built into and projecting from the wall of the tank1 or by means of a short pier of brickwork and concrete1 built up on the floor of the tank under the arm to the required level4 ,another method of drawing off the top water from tanks has been introduced by ,messrs4 ,willcox and ,raikes1 ,civil ,engineers1 and is manufactured by ,messrs4 ,adams ,hydraulics1 ,ltd4 ,as will be seen from the illustration1 ,fig4 #cj1 it consists of a cast-iron stand-pipe1 in sections1 each of which makes a tight joint with the one below it4 ,a spindle1 working in a screwed nut in a bracket or pillar at the top1 passes through crossbar guides inside the stand-pipe sections4 ,this spindle has projections at irregular intervals1 arranged in such a manner that as the spindle is screwed up it lifts the top section first1 then the second1 and lastly the third1 and thus makes it possible to draw off the supernatant water in three layers1 each of which may if desired be discharged in different directions4 ,finally1 the sludge may be drawn off through the same outlet to the sludge-disposal area4 ,illustration3 ,,fig4 #ca4 ,as the distance which the sewage travels in 8continuous flow settlement tanks with chemicals0 is frequently an important factor in securing the maximum efficiency1 it may be found economical to arrange the tanks in the form shown in ,fig4 #ca1 where each tank has a division wall1 carried through from the inlet end to within a few feet of the opposite end1 so that the sewage travels a distance equal to twice the length of the tank before passing to the outlet4 ,this arrangement requires only one carrier1 but this must be provided with suitable sluice-gates opposite to each tank1 in addition to similar gates on the inlet and outlet from each tank4 ,the ,dortmund type of tank1 described under the heading of detritus tanks1 may also be adapted for sedimentation tanks1 but the outlet should be arranged in such a manner as to reduce the velocity of the flow at this point to the minimum4 ,this is usually secured in by causing the liquid to flow over a weir formed by the circular wall of the tank1 or by a number of weirs consisting of cast-iron channels laid transversely across the top of the tank4 ,in either case it becomes necessary to form a circular effluent channel round the top of the tank1 to receive the effluent after it has passed over the weirs4 ,these two arrangements are illustrated in ,figs4 #cb and #cc1 the former showing the circular weir wall1 and the latter the transverse cast-iron channels4 ,both edges of each of these channels act as weirs1 so that the total effective length of weir is thus greatly increased4 ,the inlets1 conical bottoms1 and sludge outlets for these two tanks1 would be similar to those shown in connection with this form of detritus tank 7,fig4 #ad74 ,mr4 ,s4 ,r4 ,lowcock1 ,m4,inst4 ,c4,e41 has stated that in his experience an excellent effluent can be obtained by drawing off the liquid at one point1 and at about two feet below the top water level4 ,a method of accomplishing this is shown in dotted lines on ,fig4 #cb4 ,illustration3 ,,fig4 #cb4 ,special ,types of ,tanks4--,one of the troubles which frequently arises in the operation of all types of natural sedimentation or septic tanks is a nuisance from smell1 due to offensive gases given off by the effluent4 ,these are the result of the decomposition under anaerobic conditions of the organic matter deposited in the tanks4 ,it is possible to arrange them in such a way1 that the conditions which cause the trouble may to a great extent be avoided even in the ordinary types of tanks4 ,illustration3 ,,fig4 #cc4 ,hydrolytic ,tank4--,there are1 however1 several types specially designed to eliminate these troubles altogether1 by separating the flow of sewage through the tank from that section in which the composition of the sludge takes place4 ,among these is the hydrolytic tank4 ,this tank is already well known to most engineers1 in the original form designed by ,dr4 ,w4 ,owen ,travis1 and adopted at ,hampton-on-,thames1 but a new and improved method of construction has recently been brought out4 ,the principle of this tank may be described as the deposition and collection of the impurities in sewage by a process of physical de-solution1 the matters being separated in the order of their grossness and specific gravity1 namely 7a7 the removal of the grosser solids by means of screens2 7b7 the settling of the heavy inorganic solids in a detritus chamber2 and 7c7 the separation of the lighter solids in suspension and in a colloidal state4 ,finally1 means are provided whereby the deposit in the various chambers may be collected and removed with facility4 ,it is impossible in the space available to describe in full the reasons for the various details of construction which have been adopted1 but the accompanying illustrations1 ,figs4 #cd to #db1 which have been kindly furnished by ,messrs4 ,shone and ,ault1 ,civil ,engineers1 illustrate an example of the latest type of the tank4 ,fig4 #cd is a plan section of the tank1 and ,figs4 #ce to #db are vertical sections on the lines indicated4 ,the tank is by preference circular1 as shown4 ,the sewage is delivered from the pipe ,s through a screening chamber1 in which the gross matters1 such as rags and vegetable debris are retained on the screen ,a1 and are from time to time removed by hand or mechanically4 ,the sewage passes over the weir a into the first section ,b1 which occupies about one-eighth of the circumference and is divided into two parts by the diaphragm b1 ,fig4 #ce4 ,the flow of the sewage through this first section ,b may1 by the weirs b#a and b#b1 be so appointed that two-thirds of it flows from the outer compartment over b#a and one-third over b#b from the inner compartment1 the only entrance to which is by the opening b#c1 ,fig4 #ce1 in the bottom of the diaphragm b2 so that the deposition of the solids by gravity is accelerated by the flow of the one-third of the sewage into the inner part of the compartment ,b4 ,the solids collect in the conical bottom part b#d1 ,fig4 #ce4 ,the overflows from the weirs b#a and b#b1 are1 by the channels b#e and b#f1 directed to the downtake c1 ,figs4 #cd1 #ce1 #ch and #ci1 which delivers the sewage near the bottom of the outer compartment ,c1 which latter1 with the inner compartment ,d1 forms the second section of the tank4 ,these two compartments are divided by the diaphragm c#a1 ,fig4 #ci1 having openings c#b in the lower edge4 ,in the drawing the second section of the tank is shown divided in two parts by the wall and weirs c#c1 ,figs4 #cd and #dj1 and they occupy together about seven-eighths of the circumference of the tanks4 ,the weirs c#c are so proportioned that #he per cent4 of the liquid passes directly through the outer compartment1 and #ae per cent4 indirectly through the inner compartment of the first portion of the second section of the tank1 into the respective compartments of the second portion of that section4 ,it should be noted that the only passages for the flow of liquids into the inner compartment are the openings c#b1 ,figs4 #cd and #ci2 and consequently the deposition of solids is accelerated by this flow1 so that they collect in the lower part1 c#d1 ,fig4 #ce1 of the inner compartment ,b4 ,the flow through the second portion of this second section of the tank is governed by the weirs e#e and e1 ,figs4 #cd and #cf1 which weirs are shown of such proportion as to cause #gj per cent4 of the liquid to flow directly through the outer compartment1 and #cj per cent4 indirectly through the inner compartment4 ,the colloiders c#f1 ,figs4 #cd and #ce1 are fixed vertically in the outer compartments to attract and absorb the solids in pseudo solution4 ,it will thus be clear that #gj per cent4 of the sewage flows in a direct manner through the outer compartment1 and in doing so deposits practically the whole of its permanent and a considerable portion of its convertible solids4 ,the effluent from the inner compartment ,d of the second section of the tank is1 by the submerged channel e#c1 ,fig4 #cf1 passed into the supplementary section ,e1 which is fitted with colloiders1 e#a1 ,figs4 #cd1 #ce1 and #da4 ,this effluent1 which has become fouled by the disturbance caused by the evolution of gases in the inner compartment of the second section1 is thus submitted to a further de-solution action by absorption and other processes4 ,finally the outflow from the outer compartment ,c1 of the second section over the weir e#e1 ,figs4 #cd and #cf1 and the outflow from the supplementary section ,e1 over the weir e1 are passed away from the tank by a common channel1 e#d1 ,figs4 #cd and #cg1 whence the effluent may1 for further treatment1 be led to filters or on the land4 ,the overflows from the two weirs may1 however1 be led away from the tank by independent channels for separate treatment4 ,the solids1 collected in the form of sludge in the lower parts of the sections1 can be drawn off periodically through the pipes c#g1 ,figs4 #cd1 #ce1 #da1 and #db1 governed by valves into the central chamber ,f1 ,figs4 #cd and #ce1 from which it may be led by the pipe f to adjoining land1 or elsewhere for further treatment4 ,the lighter solids1 that collect in the form of scum on the surface of the liquid in the tank1 may be skimmed off or drawn into the channels g1 ,figs4 #cd1 #ch1 and #dj1 and conducted to the central chamber ,f1 and disposed of similarly to the sludge4 ,the tank is1 or may be1 constructed of concrete1 which may be reinforced as required according as it is wholly or partly above the ground4 ,its shape may be greatly varied according to local requirements and other considerations4 ,illustration3 ,,fig4 #cd4 ,illustration3 ,,fig4 #ce4 ,illustration3 ,,fig4 #cf4 ,illustration3 ,,fig4 #cg4 ,illustration3 ,,fig4 #ch4 ,illustration3 ,,fig4 #ci4 ,illustration3 ,,fig4 #dj4 ,illustration3 ,,fig4 #da4 ,illustration3 ,,fig4 #db4 ,,hydrolytic ,,tank4 ,imhof ,tank4--,a somewhat similar tank has been introduced in ,germany1 and is known as the ,imhof tank2 but in this case the whole of the sewage is passed through direct to the outlet1 and none is allowed to flow through the portion in which the decomposition of the sludge takes place4 ,these tanks are known in ,germany as 8,emscherbrunnen10 from the district in which they were first introduced4 ,the present type has been designed by ,dr4 ,imhof1 the engineer to the ,emschergenossenschaft at ,essen1 in ,germany1 and is shown1 ,fig4 #dc4 ,it should be noted that the arrangements may be varied in special cases4 ,where the daily flow is considerable1 at least two such tanks are recommended1 and the inlets and outlets are so arranged that the direction of the flow may be reversed at regular intervals1 in order that both tanks may receive an equal proportion of the solid matters4 ,the method of removal of the sludge is usually arranged on the same lines as that previously described in connection with the ,dortmund type of detritus tank4 ,it is1 however1 evident that difficulties are occasionally experienced in drawing off the sludge when it has been allowed to remain in the tanks for long periods untouched1 as it is suggested that a connection from the water supply service may be carried down to the bottom of these tanks1 to permit of a jet of water under pressure being directed upon the sludge in order to stir it up and thus facilitate its withdrawal4 ,illustration3 ,,fig4 #dc4--;,,imhof ,,tank4 ,skegness ,tank4--,with the same end in view--the separation of the process of sludge liquefaction from the bulk of the sewage flow--,messrs4 ,elliott and ,brown1 ,civil ,engineers1 devised an ingenious arrangement of tanks for the scheme of sewage disposal which they carried out at ,skegness4 ,in this installation the sewage first enters a settling tank on the ,dortmund principle1 from which it overflows at the top into a dosing tank which gives intermittent discharges to the filters4 ,the usual sludge delivering pipe from the settling tank is connected into the bottom of a separate sludge liquefying tank1 the floor of which is some four or five feet below the top water-level of the settling tank4 ,the upper part of the sludge liquefying tank is also connected to the dosing tank in such a way1 that when the latter discharges it draws off several inches depth of the supernatant water from the top of the sludge liquefying tank at each discharge4 ,the result of this operation is1 that each time the dosing tank is discharged an artificial difference in level is created between the top water levels in the settling tank and the sludge liquefying tank--the latter being the lower of the two--and as they are in direct communication through the sludge pipe1 the extra head in the settling tank causes a movement to take place through the sludge pipe1 and thus forces some sludge up into the sludge liquefying tank1 where it remains for any desired period for liquefaction without unduly fouling the tank liquor delivered to the filters4 ,illustration3 ,candy-,whittaker ,patent ,bacterial ,sewage ,purification ,tank ,sectional ,elevation ,,fig4 #dd4 ,candy-,whittaker ,bacterial ,tank4--,somewhat similar in form to some of the previously described tanks1 the ,candy-,whittaker bacterial tank is circular in plan and provided with a deep inner cone1 which divides it into two compartments as shown1 ,fig4 #dd4 ,the sewage enters the outer compartment through a pipe1 by means of which it is evenly distributed4 ,the outlet is through submerged effluent troughs situated inside the cone1 so that the sewage must flow down to within a short distance of the bottom of the tank in order to pass under the bottom of the cone and reach the outlet troughs4 ,in consequence of this method of construction1 the bulk of the solids in suspension are deposited in a circular ,v-shaped gutter or sump1 from which the sludge is removed by the pressure due to the head of water forcing it up a sludge pipe similar to that previously described in connection with the ,dortmund type of tank4 ,in the ,candy tank1 however1 the inlet end of the sludge pipe has a returned end with a swivel joint1 which is rotated by means of a vertical spindle operated by a crank handle at the side of the tank1 working through suitable gearing4 ,it is claimed that any scum which may be formed on the surface by floating solids1 or by sludge freed from the bottom of the tank by gases produced by fermentation1 is retained in the outer compartment1 and thus prevented from passing away at the outlet with the clarified sewage4 ,non-septic ,cylinder4--,the troubles due to foul-smelling gases arising from the over-septicisation of sewage in tanks1 are very liable to occur in small installations for country houses1 where the daily volume varies periodically1 and may drop to a mere dribble when the family is away and only one or two servants are left in the house4 ,to meet the requirements of these cases1 an arrangement has been designed by ,messrs4 ,adamsez1 ,ltd41 which consists of a deep glazed fir-eclay cylinder1 provided with special inlet and outlet pipes4 ,in consequence of the small diameter of the cylinder1 the sewage passes direct through to the outlet in a very short space of time1 but leaves the solids in suspension in the cylinder1 where they undergo decomposition without affecting to any great extent the character of the fresh sewage on its way to the filter4 ,this tank is shown in connection with a small filter and special distributing apparatus in ,fig4 #de1 and is known as the 8,non-septic0 cylinder4 ,the sewage1 as it leaves this cylinder1 is well suited for further oxidation in properly constructed filters1 or on suitable land without any possibility of causing a nuisance from smell4 ,illustration3 ,,fig4 #de4--8,,non-,,septic0 ,,cylinder ,,with ,,small ,,filter4 8,kessel40--,in addition to those already described1 other ingenious devices have been designed with the same end in view1 viz4 the prevention of nuisance from smell4 ,two of these1 introduced by the ,septic ,tank ,co41 are based upon the theory that it is desirable to separate the solids in sewage from the liquid at the earliest possible moment after they enter the sewer4 ,these are illustrated in ,figs4 #df and #dg4 ,the former shows what is known as the 8,kessel10 its name in ,germany1 where it was first used4 ,briefly described1 it consists of a vacuum chamber1 in which the sewage rises1 by reason of the pressure of the atmosphere1 to a height of about #be feet1 and then flows down again through a vertical tube1 emerging from the apparatus at a level a few inches below the level of the invert of the incoming sewer4 ,it is claimed that the deposition of the solids in suspension1 due to their specific gravity being slightly greater than that of the liquid sewage1 is greatly assisted by taking place in vacuum1 and that a high percentage of the suspended solids is removed4 ,the bottom of the 8,kessel0 is in the form of an inverted cone1 to the apex of which a sludge pipe is connected1 with its outlet end delivering into a separate sludge well4 ,the deposit which takes place in the 8,kessel0 is drawn off at frequent intervals1 before it has had time to become foul1 and the capacity of the 8,kessel0 is so small by comparison with the daily flow of sewage1 that the latter passes out very slightly altered in character from the state in which it entered4 ,the apparatus is provided with various arrangements1 for ensuring its continuity of action1 for producing the necessary vacuum1 and for facilitating the removal of the sludge4 ,other advantages claimed for the system are that it is constructed above the level of the sewer1 so that costly construction below ground is avoided1 and that only a few inches of fall are lost between the inlet and the outlet4 ,illustration3 ,,fig4 #df4--8,,kessel0 ,,tank4 8,separator40--,the second apparatus shown in ,fig4 #dg is of an entirely different character1 and is aptly designated by the term 8,separator40 ,it consists of a number of comparatively shallow settling tanks1 each provided at the top with a metal grating1 the separate bars of which are in the form of narrow channels1 with open ends discharging into a common effluent carrier4 ,the edges of these channels are accurately planed to form weirs1 over which the liquid portion of the sewage flows in an extremely thin film4 ,these channels are provided with adjusting set-screws1 so that they may all be set at exactly the same level1 and thus ensure a uniform depth of flow over the edges of the whole of the channels in each tank4 ,the combined length of the channels in each tank form a weir of comparatively enormous width1 so that the velocity with which the sewage approaches the edges of the channels is extremely low1 with the result that a high percentage of the matters in suspension are arrested in the tank and are slowly deposited to form sludge4 ,the bottom of each separate compartment of these tanks is in the form of a sump provided with a sludge valve connected to a common sludge delivery pipe1 leading to the sludge disposal area by gravity if the latter is at a lower level or to a sludge well if the tanks are below ground4 ,in order to prevent the decomposition of the sludge from proceeding so far as to cause a nuisance from smell1 the deposit in the tanks is drawn off at frequent intervals4 ,illustration3 ,,fig4 #dg4--8,,separator0 ,,tank4 ,illustration3 ,,fig4 #dh4--,,the 8,,fieldhouse0 ,,tank4 ,the 8,fieldhouse0 ,tank4--,this is illustrated in ,fig4 #dh 7from a drawing supplied by the patentee1 ,mr4 ,j4 ,fieldhouse7 from which it will be seen that the sewage enters the central chamber ,a#a by the inlet pipe ,m1 the end of which is turned down to deliver the sewage immediately over the inverted cone ,c4 ,between the inverted cone ,c and the side of this chamber an annular space ,e is provided1 so that the solids which are deposited may find their way into the cone-shaped sludge chamber below1 from which they are drawn off by means of valve ,d and sludge pipe ,f4 ,the liquid passes from the central chamber ,a#a through the walls on all sides into the outer tank ,b#a1 by way of the oblique passages ,h1 by which the liquid is deflected in a downward direction1 and eventually flows over the outer circular weir ,k into the effluent channel ,l4 ,the outer tank ,b#a is divided into sections1 each of which is provided with a sludge sump and sludge valve ,n4 ,scum-boards are provided both radially ,t1 and in front of the weir ,j1 and the latter may be lowered when it is desired to draw off the scum4 ,this operation is performed by closing slides ,s#a1 so as to cause the sewage to head up in the tank1 and the scum of any section may then be drawn off by lowering the particular end board ,j next to the weir ,k1 and allowing the scum to overflow into the effluent channel ,l and thence to the sludge bed4 ,the special features of this tank are3--7a7 the cone-shaped bottom of each section1 to facilitate the withdrawal of the sludge without discharging the liquid contents2 7b7 the oblique passages ,h in the wall between the inner and outer tanks1 for the purpose of deflecting the flow of the sewage in a downward direction1 and thus assisting the deposition of the matters in suspension2 7c7 the removable scum boards in the outer tank1 to allow of the removal of the scum2 7d7 the general design by which the sewage enters at the centre1 and thence spreads in all directions until it flows in a thin film over a weir of comparatively enormous length1 thereby causing a gradually increasing reduction in the velocity of the flow1 and thus providing every facility for the deposition of a very large percentage of the matters in suspension4 ,illustration3 ,,fig4 #di4--,,slate ,,beds ,,in ,,course ,,of ,,construction4 ,slate ,beds4--,from the foregoing it will be gathered that there is a growing tendency to reduce the process of putrefaction in tanks under anaerobic conditions to the minimum1 consistent with the removal of solids4 ,if this theory is carried to its logical conclusion1 it would appear to point to the elimination of all anaerobic conditions4 ,that this is not generally done is probably due to the fact that a preliminary process of putrefaction to some extent1 is1 by many1 considered essential in the removal of solids in sewage4 ,on the other hand1 there are some who are not of this opinion4 ,mr4 ,w4 ,j4 ,dibdin has always contended that putrefaction is not necessary1 and his system of slate beds is designed as a preliminary process in which the conditions are purely aerobic4 ,fig4 #di shows details of this system1 from which it will be seen that it consists essentially of a watertight tank filled with superimposed layers of plates1 usually about #b inches apart4 ,in order to prevent any misunderstandings1 it should be noted that the description 8slate beds0 has arisen through the adoption of thin slate slabs1 with distance pieces of slate blocks1 as the most economical method of construction4 ,no special value is ascribed to the slate itself1 beyond its cheapness in the particular form required and its durability1 it being practically everlasting4 ,the essence of the system is the use of horizontal plates to receive and retain the deposit of solid matters in suspension in the sewage1 so that they are decomposed or digested1 after the settled liquid has been drawn off1 by aerobic bacteria and other higher forms of life1 including worms1 all of which thrive only in the presence of air4 ,the beds are filled with the raw sewage1 which is then allowed to remain for a period of about two hours for quiescent settlement1 after which the liquid is slowly drawn off4 ,it is true that during the period of standing full the solids in the sewage are not actually in the presence of air1 but it is claimed that a certain amount of air is retained on the under side of the plates1 and the oxygen thus available1 in addition to the oxygen present in the raw sewage1 is sufficient to prevent the setting up of putrefaction during the comparatively short period of standing full4 ,as the liquid is drawn off1 air enters freely between all the layers1 so that the deposited solids are then immediately brought into close contact with air1 from which the aerobic bacteria and other organisms can draw the oxygen they need for their life functions4 ,the result is that the ultimate residue of solids is of quite a different character from sludge of the ordinary type4 ,it is of a granular nature1 which rapidly dries on a properly constructed draining bed1 and1 when dry1 resembles ordinary peaty mould4 ,independent information as to the actual amount of ultimate solid residue resulting from this system is not yet available1 but it is generally admitted that1 when properly operated1 putrefaction does not occur at any stage of the process1 and that there is an entire absence of nuisance from smell throughout the works4 ,when new1 these slate beds have a liquid capacity of over #hj per cent4 of the gross capacity of the beds1 but it is usual1 in calculating the size of the beds required for a particular volume of sewage1 to allow for a normal working capacity of #ff per cent4 of the gross capacity1 and to provide for one filling per day in dry weather4 ,these beds are generally constructed with a working depth of #c--d feet1 but they may be as little as #a foot in depth where it is necessary to reduce the total fall required for the works to the minimum4 ,the residue of the solids after treatment in these beds passes out in the effluent1 and it is understood that it has not been found necessary to wash out the beds or remove the deposit on the slates themselves1 even after several years of operation with strong sewage4 ,in designing beds for this system1 the chief points to be borne in mind are that the constructional work shall be absolutely watertight1 and that the fall on the floor shall be sufficient to allow the solid residue to pass freely to the outlet with the effluent4 ,the beds may be operated by hand by means of penstocks on the inlets and outlets1 or automatically by means of special apparatus of the type which will be described later in connection with contact-beds4 ,it is1 however1 important that the liquid shall not be discharged from the beds at too rapid a rate4 ,,sludge ,,disposal4 ,sludge ,removal4--,in connection with the discharge of sludge from tanks of any kind1 there are several appliances adapted to meet the requirements of particular cases4 ,where the sludge-disposal area is at a lower level than the bottom of the tank1 a simple sludge-plug or penstock on the inlet to the sludge-pipe may be used1 or a sluice valve may be inserted on the sludge-pipe after it leaves the tanks4 ,where the sludge-disposal area is #b feet or more below the level of the surface of the sewage in the tank1 and the floor of the latter is provided with a suitable sump in which the sludge may accumulate1 the method of withdrawing the sludge by utilising the pressure of the head of liquid in the tank1 as described in connection with the ,dortmund type of detritus tank1 may be adopted with advantage4 ,in cases where it is necessary to raise the sludge to the disposal area1 a hand-operated chain-pump may be used for small schemes1 or for large volumes1 and where power is available1 sludge elevators of the bucket type1 as shown on pages #dj to #db1 and manufactured by ,messrs4 ,s4 ,s4 ,stott and ,co41 ,messrs4 ,ham1 ,baker and ,co41 ,ltd41 and ,messrs4 ,adams ,hydraulics1 ,ltd41 will be found convenient4 ,these appliances are usually erected in special sludge wells1 to which the sludge is delivered by gravity4 ,in the case of long tanks1 in which the floors are comparatively flat1 and especially where the sludge is allowed to accumulate until it has become consolidated to a great extent1 difficulties are experienced in causing the sludge to flow to the outlet by gravity4 ,this usually involves the employment of men to descend into the tank and force the sludge towards the outlet by means of squeegees1 a slow and laborious process4 ,illustration3 ,,fig4 #ej4--;,,chemical ,,mixer4 ,chemical ,mixers4--,the methods adopted for adding the necessary chemicals to sewage for chemical precipitation are various4 ,where alumina-ferric is used1 the simplest method is to place blocks of the precipitant in wire cages placed in the inlet channel so that the flow of the sewage itself dissolves the block as required4 ,it has been found that this method is not economical in some cases1 and the precipitant is dissolved beforehand in a suitable mixer in order that it may be added to the sewage in the form of a solution4 ,this applies specially to the lime process1 and several forms of these mixing machines are shown in ,figs4 #ej1 #ea and #eb1 made by ,messrs4 ,goddard1 ,massey and ,warner1 ,messrs4 ,manlove1 ,alliott and ,co41 ,ltd41 and ,messrs4 ,s4 ,h4 ,johnson and ,co41 ,ltd4 ,these may be driven by power or by the flow of the sewage itself1 but the most important point which requires attention is that the strength of the solution shall vary with the strength of the sewage1 either by varying the rate of flow of a solution of uniform strength1 or by varying the strength of a solution flowing at a uniform rate4 ,illustration3 ,,fig4 #ea4--;,,chemical ,,mixer4 ,sewage ,mixers4--,even after the chemical solution has been added to the sewage1 it is necessary to make sure that it is thoroughly mixed with the sewage4 ,the simplest method of doing this is by means of baffle-plates fixed in the channel leading to the tanks4 ,other methods are by paddle-wheels driven by the sewage itself2 by allowing the sewage to drop in a chamber on to a projecting pier or stone2 by using power to drive 7a7 a plunger moving up and down in a sump1 7b7 a vertical shaft to which horizontal paddles are attached to rotate in the sewage channel1 7c7 to operate a device similar to the well-known mechanical egg-whisk1 7d7 or to force compressed air through a perforated pipe laid in the sewage channel4 ,indeed1 there is no end to the various mechanical devices which are used for this purpose4 ,illustration3 ,,fig4 #eb4--,,pneumatic ,,chemical ,,mixer4 ,illustration3 ,,fig4 #ec4--,,sludge ,,press4 ,illustration3 ,,fig4 #ed4--,,sludge ,,press4 ,sludge ,presses4--,when it is desired to reduce the liquid content of the sludge as far as possible1 the general practice is to make use of sludge presses for this purpose4 ,several types are illustrated in ,figs4 #ec1 #ed and #ee1 manufactured by ,messrs4 ,manlove1 ,alliott and ,co41 ,ltd41 ,messrs4 ,goddard1 ,massey and ,warner1 and ,messrs4 ,s4 ,h4 ,johnson and ,co41 ,ltd4 ,all are based upon the principle of compressing the liquid sludge under high-pressure between iron plates which support cloth or other filtering material1 through which the liquid passes into grooves on the faces of the plates1 and thence by way of conduits in the plates themselves to the floor below4 ,the several makes have different methods of opening and closing the plates1 and the presses are made of various sizes for operation by hand or by power4 ,fig4 #ef shows a complete sludge-pressing plant as designed by ,messrs4 ,s4 ,h4 ,johnson and ,co41 ,ltd4 ,the description of the details of this plant is as follows4 ,illustration3 ,,fig4 #ee4--,,sludge ,,press4 ,the sewage enters the works by the channel ,a1 and passes first through the bar screen ,b4 ,the screening is necessary to remove anything that would tend to produce obstruction in the inlets to the press chambers and be liable to cause breakage of the press plates4 ,the sewage next meets with the milk of lime from the lime mixer ,c1 with which it is mixed by flowing along the gravitation mixer ,d4 ,the pneumatic lime mixer produces lime milk of a constant strength1 and the flow is adjusted in proportion to the requirements of the sewage4 ,should it be necessary to add sulphate of alumina to the sewage1 this is produced by the pneumatic alumina mixer ,e1 and is added to the sewage after the latter has been thoroughly mixed with lime4 ,air for working the pneumatic lime and alumina mixers is provided by the blowing engine ,r4 ,the treated sewage then passes further along the zigzag channel into the precipitating tanks ,f1 the ends of two of which are shown in the drawing4 ,it is advisable to have two or more tanks1 so as to allow sufficient time for precipitation4 ,the usual capacity of the precipitation tanks is equal to #f hours' flow of the sewage1 and they may continue running1 overflowing continuously1 for a considerable time1 but not so long as will produce putrefactive decomposition and thereby cause a nuisance4 ,the precipitation tanks1 which are cleared out alternately1 are provided with hinged flap valves ,g and underground stoneware pipes to convey the sludge into the liming sump ,h1 the top water being first decanted off4 ,in the liming sump the sludge is limed with milk of lime from the lime mixer ,i1 which is also worked by the blowing engine ,r above referred to4 ,from the liming sump the sludge passes into the sludge tank ,j1 by means of the pair of automatic rams ,k4 ,the automatic rams work alternately1 one filling by means of vacuum1 whilst the other is being discharged by means of compressed air4 ,as soon as the one is emptied and the other filled1 the action is reversed1 and so on1 each filling and emptying alternately1 thereby keeping up a continuous discharge4 ,by being drawn into the rams1 and thence forced into the sludge tank1 the sludge becomes thoroughly mixed with the lime4 ,this liming of sludge causes a considerable further deposition and concentration of the sludge1 and after standing all night the supernatant water is decanted off by the skimmer ,l4 ,the sludge1 now ready for pressing1 is allowed to run by gravitation into the automatic rams ,k previously referred to1 and thence discharged into the sludge presses ,m by means of compressed air1 the compressed air being supplied by the air-compressor ,n1 which also acts as a vacuum pump for drawing the sludge from the sludge pump into the automatic rams4 ,the solid portion of the sludge is retained in the chambers of the sludge presses by the filter cloths1 the effluent being discharged into the trough at the side of each press1 and thence by down pipes and gullies into the effluent channel ,o1 being treated again in the gravitation mixer1 and finally flowing away with the effluent from the precipitating tanks4 ,the press chambers are known to be filled with solid sludge cakes1 when effluent ceases to flow from the outlets of the chambers4 ,the presses are then opened and the cakes discharged into a tipping truck ,q1 by which they are removed to the final disposal site4 ,illustration3 ,,fig4 #ef4--;,,complete ,,sludge-,,pressing ,,plant4 ,illustration3 ,,fig4 #eg4--,,sludge-,,drying ,,apparatus4 ,illustration3 ,,fig4 #eg4--,,sludge-,,drying ,,apparatus4 ,hydro-extractor for ,sludge4--,an entirely different method has been adopted in the special apparatus in use at ,hanover and other towns in ,germany1 the ,schaefer-ter-,mer centrifugal sludge de-hydrating apparatus manufactured by the ,hanoversche-,maschinenbau ,a4-,g41 vormals ,georg ,egestorff1 and illustrated in ,fig4 #eg4 ,in this apparatus the centrifugal force resulting from the rapid rotation of the drum into which the liquid sludge is fed1 is utilised to throw out the solid matters from the centre towards the circumference1 where they are caught in the outer part of the drum of the machine4 ,the drum revolves continuously1 but at regular intervals it is opened automatically in sections for a brief period1 so that the dry sludge is thrown outwards against the fixed casing and thus becomes broken up and falls to the bottom1 and thence to an endless-band transporter by which it is discharged outside the building4 ,at the moment when the sections of the outer casing of the drum of the machine are opened to allow the dry sludge to be thrown out1 the wet sludge is prevented from passing into these sections by the automatic closing of the inner slide door1 which is opened as soon as the outer slide is closed4 ,the water extracted falls into an annular channel below1 from which it flows1 by way of a pipe1 back to the settling tanks to be treated again4 ,the result of a series of special tests of this apparatus showed that the liquid contents of the sludge was reduced from #ib per cent4 to #ej per cent4 ,the installation at ,hanover has now been in operation since ,june #aijh1 dealing with a daily volume of #ff million gallons of sewage from a population of #bhj1jjj4 ,from particulars supplied by the town authorities1 it appears that the total cost of operating the complete plant1 including the settling tanks and the sludge treatment apparatus1 amounts to about #hs4 per million gallons of sewage treated1 or about #jh;d4 per head of population per annum4 ,messrs4 ,manlove1 ,alliott and ,co41 ,ltd41 have now entered into an arrangement with the above-mentioned firm to take up the control of the patents and the sole manufacture and sale of the ,schaefer-ter-,mer ,sludge-,drying ,apparatus in ,great ,britain and the ,colonies4 ,illustration3 ,,fig4 #eh4--,,sludge-,,draining ,,bed4 ,sludge ,draining ,beds4--,although the methods of disposal of sludge must vary in different localities according to the means available for the purpose1 and most of them involve very little1 if any1 constructional work1 it may be desirable to describe the various points which should be taken into consideration in the construction of suitable draining beds1 as these should be included in the original design of any scheme in which they are to be used4 ,their chief function is to provide means for removing the maximum amount of the liquid contents of the sludge in the minimum of time1 and it is obvious that this desideratum can only be secured by spreading out the liquid sludge in thin layers upon material through which the liquid may readily pass without carrying with it any of the sludge4 ,the first of these requirements necessitates the provision of an ample area of draining surface1 and the second involves the use of a suitably graded material provided with ample means of drainage4 ,the beds themselves may be simple excavations in the ground1 as shown in ,fig4 #eh1 or may be constructed of brickwork or concrete1 but in either case it is absolutely essential that the floor should be covered with tiles1 or other means of sub-drainage1 leading to a free outlet1 which should be connected to the screen chamber1 detritus tanks1 pump well1 or some other point at the inlet to the works1 so that it may be treated over again with the crude sewage4 ,whatever material is used for filling the bed1 the lower portion which is placed on the floor and over the drainage tiles should be of large size1 #b inches to #c inches in diameter4 ,the next layer should be #a inches to inch in diameter1 and the top layer #f inches to #i inches in depth1 should be fine material inch to inch in diameter4 ,in the author's opinion1 coke-breeze will probably be found to be the best material for the top layer1 and it would be a good precaution to provide beforehand a quantity of this material in reserve to replace what is lost in removing the dried sludge from the surface of the beds4 ,it will be found advisable in operating these beds to discharge the sludge from the tanks in small quantities at frequent intervals1 rather than in large quantities at long intervals1 and it is very important that each layer of dried sludge should be removed before the next layer is delivered to the bed4 ,it cannot be too strongly urged that sludge disposal needs as much care and attention as any other stage of the process of sewage disposal1 and if this is available1 and ample area of draining beds is provided1 there should be no difficulty in solving this usually troublesome problem4 ,,percolating ,,filters4 ,in approaching the subject of the design of filters for the purpose of oxidising the organic matters--in solution and in suspension--contained in the liquid which leaves the preliminary process in tanks1 the first consideration is the question of site4 ,where the slope of the ground permits of the construction of the filters on or above the ground level1 much expense for excavation may be avoided1 so long as the base of the filter can be laid on solid ground4 ,in cases where the site of the works is comparatively flat1 it is impossible to avoid excavation1 and other means must be adopted to keep the actual cost as low as possible consistent with efficiency4 ,general ,design4--,taking the latter case first1 it should be observed that some engineers consider it desirable to construct retaining walls under all circumstances1 but the author does not agree with this idea4 ,in the first place the walls do not1 of themselves1 have any influence on the efficiency of the filters in producing a satisfactory effluent1 and if a filter can be constructed without them there is no reason why they should not be omitted4 ,this applies especially where the filters have to be constructed entirely below the surface of the ground4 ,the chief point to be considered is that the effluent shall have a free outlet1 with facilities for inspection4 ,in the case of all filters1 the best method of securing a free outlet for the effluent is to provide the floor with a suitable slope from the centre to all sides4 ,when the floor is at some depth below ground this requirement necessitates an effluent channel on all sides of the filter4 ,two methods of carrying this into effect are illustrated1 ,figs4 #ei and #fj4 ,fig4 #ei shows one retaining wall for the filter and an additional retaining wall for the surrounding earth1 carried up to the surface with the effluent channel between the two walls4 ,in ,fig4 #fj the arrangement is similar1 but the outer wall is a dwarf wall to form the effluent-channel1 and the surrounding earth is cut back to a slope of natural repose1 the earth bank usually being sown with grass or covered with turf4 ,it is essential that the outer wall shall be carried up above the toe of the earth bank1 in order to prevent soil being washed down into the effluent-channel1 but a surface-water drain should be laid to take any water that may accumulate at the back of this wall4 ,these methods of construction would1 however1 only be adopted by those who consider it essential to provide means for lateral aeration to the filter by constructing the retaining wall for the filter itself of pigeon-hole brickwork4 ,in the author's opinion1 however1 lateral aeration on these lines is altogether ineffective4 ,it can only affect the filter material for a distance of a foot or two from the wall4 ,it is true that in some cases horizontal perforated ventilating pipes have been provided1 radiating from the centre of the filter to the outer wall and terminating with open ends on the outside4 ,the effect of these is1 however1 dependent almost entirely upon the temperature of the atmosphere and the direction of the wind1 and even if they do induce air currents into the body of the filter the air will pass along the line of least resistance1 and therefore find its way through those interstices which are open and not through those which are choked in any way and thus most in need of aeration4 ,the author believes that the aeration of a filter is most effectively secured by the action of the sewage itself1 as it falls from the surface to the floor drawing in the air from the top1 and that if this is not effective1 no amount of lateral openings will produce the desired result4 ,if this contention is correct1 there is no need to incur the additional expense involved in the construction of retaining walls1 and the filters may be designed on the lines indicated in ,fig4 #fa1 where the filtering material fills the whole of the natural excavation1 and no walls are required4 ,it is true that this method involves an increase in the amount of filtering material beyond what is actually in use1 and the cost of this must be set against the cost of the wall in the alternative method shown in ,fig4 #fb1 as the cost of the excavation in either case is about the same4 ,much will depend upon the cost of the filtering material in different localities4 ,illustration3 ,,fig4 #ei4 ,illustration3 ,,fig4 #fj4 ,illustration3 ,,fig4 #fa4 ,illustration3 ,,fig4 #fb4 ,in both these methods it will be noticed that there is no outer effluent channel1 and that the floor slopes from the circumference to the centre1 where an effluent receiving chamber is constructed1 from which an effluent discharge pipe leads to the next stage in the process4 ,this is not quite so satisfactory as the arrangement shown in ,figs4 #ei and #fj1 but it is the most convenient under the circumstances4 ,when it is possible to place the filter floor on or within #b feet of the surface of the ground1 the method illustrated in ,fig4 #fj is the design most commonly adopted4 ,sometimes the arrangement of the floor shown in ,figs4 #fa and #fb is preferred4 ,there is1 however1 still another type of floor which is applicable to this case4 ,this is illustrated in ,fig4 #fc1 from which it will be seen that the whole of the floor slopes in one direction1 and the effluent is thus discharged over one-half of the circumference of the filter1 with the result that the effluent channel is only one-half the length of that required in the case of ,fig4 #fj4 ,floors of ,filters4--,in all cases the floors for percolating filters should be of a substantial character4 ,they are usually constructed of cement concrete4 ,the thickness of the concrete will depend upon the nature of the subsoil1 but in any case it should be increased at the centre in order to provide a safe foundation for the revolving sprinkler4 ,the surface of the floor should be smooth1 so as to facilitate the flow of the effluent1 and any suspended solids it may contain1 to the outlet4 ,from the preceding illustrations it will be noted that the slope of the floor may be in three directions3 7a7 from the centre to the circumference1 7b7 from the circumference to the centre1 or 7c7 from one side of the filter to the other1 a uniform slope in one direction along the diameter of the filter4 ,it has been suggested by some that the floor should consist of a series of alternate ,v-shaped ridges and furrows1 with slopes at right angles to the general slope of the floor1 but this has the disadvantage that it causes difficulties in arranging the floor tiles and placing the filtering material in position1 and further it increases the cost of construction without providing any real compensating advantages4 ,illustration3 ,,fig4 #fc4 ,illustration3 ,,fig4 #fd4--;,,floor ,,tile4 ,illustration3 ,,fig4 #fe4--8,,newham0 ,,floor ,,tile4 ,sub-drainage4--,it has been recommended that the floors should be laid with a gradient of about #a in #ajj1 but the author believes that it would tend to assist the free discharge of the suspended solids in the effluent if this gradient were increased to #a in #ge1 or even #a in #ej1 and that if this were done1 there would be no need to make any special provision for access to the under drains for cleaning purposes4 ,another important factor in securing a free discharge of the suspended solids1 is the use of proper floor tiles or sub-drains4 ,the old idea of laying rows of agricultural pipes with open joints1 or even of perforated pipes1 on the floor has been proved to be useless4 ,in some cases it is considered sufficient to have rows of floor tiles1 laid at any distance apart up to #aj feet at the circumference4 ,there is1 however1 very little doubt that the only correct method is to support the whole of the filtering material on a complete false floor1 so that the suspended solids which are carried down with the effluent1 and thus reach the bottom of the filter at all points of its area1 may fall freely into an open space1 from which they will be carried away with the least possible obstruction by the flow of the liquid4 ,it is certain that these suspended solids have a great tendency to adhere to any object with which they may come in contact1 and that this can only be avoided by providing a free space immediately above the floor and over its whole area4 ,the nearest approach to this acme of perfection is a complete false floor1 with openings too small to allow the filtering material to pass through1 but large enough to give a free passage to the suspended solids4 ,one of the simplest methods is to form the false floor of bricks1 laid flat on rows of bricks on edge4 ,there are1 however1 several floor tiles on the market specially designed for this work4 ,a number of these are illustrated in the accompanying figures4 ,the ,ames-,crosta tile1 ,fig4 #fd1 has a simple flat top with corrugated edges supported on four short legs4 ,when placed close together1 the corrugations form apertures through which the liquid passes1 and the flat tops form a table which provides every facility for placing the filtering material in position4 ,a somewhat similar floor tile is the 8,newham0 shown in ,fig4 #fe4 ,in this case1 however1 each tile has only two legs1 and thus there is less obstruction to the flow of the effluent4 ,the 8,stiff0 floor tile1 ,fig4 #ff1 is of much the same type as the two last described4 ,another material which has been adapted for this purpose is a single layer of the 8,dibdin0 type of slate slabs and blocks1 as shown previously in connection with the preliminary treatment of sewage in tanks1 ,fig4 #di4 ,this method also provides a complete flat false floor1 and has the additional advantage of occupying the least possible space4 ,the slabs themselves may be split to any suitable thickness1 and the supporting blocks may be cut to any size1 as little as #a inch in thickness if desired4 ,the slabs vary in shape and size1 but may be secured of larger area than tiles1 so that the necessary supporting blocks are less in number than the feet of the tiles1 and thus offer less obstruction to the effluent4 ,the apertures for the passage of the liquid are provided by the holes formed by the irregular edges of the slabs1 where they abut on one another4 ,illustration3 ,,fig4 #ff4--8,,stiff0 ,,floor ,,tile4 ,there are1 however1 floor tiles of other shapes1 such as the ,candy tile1 ,fig4 #fg1 for which it is claimed that the effective depth of the filter may be calculated from the floor1 and that the height of the ,v-shaped opening under the tile provides greater drainage and ventilation openings than other tiles4 ,other drainage tiles are semicircular in section4 ,the ,naylor tile1 ,fig4 #fh1 and the ,albion floor tile1 ,fig4 #fi1 designed and used by ,mr4 ,e4 ,e4 ,ryder1 ,surveyor to the ,bushey ,urban ,district ,council1 both have openings at the floor level4 ,the 8,mansfield0 floor tile1 ,fig4 #gj1 is the type adopted for the extensive filters at the ,birmingham ,tame and ,rea district sewage farm by ,mr4 ,j4 ,d4 ,watson1 ,engineer to the ,drainage ,board4 ,illustration3 ,,fig4 #fg4--;,,candy ,,floor ,,tile4 ,illustration3 ,,fig4 #fh4--,,naylor ,,floor ,,tile4 ,in some cases1 instead of providing a free space above the floor1 drainage channels have been formed in the floor1 with rebates in the sides to receive flat perforated tiles1 as ,fig4 #ga4 ,this method of drainage certainly leaves the floor clear to receive the filtering material1 but it has the disadvantage that it does not provide a free space under the whole of the material2 and as the suspended solids in the effluent must of necessity travel some distance before they reach a channel1 they are1 to a great extent1 arrested by the material which comes immediately on the floor1 however large the separate pieces may be1 and thus tend to choke the interstices4 ,illustration3 ,,fig4 #fi4--;,,floor ,,tile4 ,illustration3 ,,fig4 #gj4--8,,mansfield0 ,,floor ,,tile4 ,whatever method of sub-drainage may be adopted1 it is advisable to continue the tiles1 or channels1 right through to the effluent channel or chamber in straight lines1 so that the effluent may have a clear way throughout its course under the filter1 until it reaches the open effluent channel or pipe4 ,illustration3 ,,fig4 #ga4 ,walls of ,filters4--,the great diversity of methods adopted to retain in position the material of filters constructed above the level of the ground1 must be extremely perplexing to anyone who investigates the subject4 ,they vary from walls of such thickness and substantial material that they would be quite suitable for resisting the pressure of a head of water equal to the depth of the filter1 down to no walls at all4 ,in many cases walls #i inches thick throughout and #f feet in height are found to be quite satisfactory1 while in a large number of cases the material itself1 when it consists of clinker1 is found standing in an almost vertical position with perfect success4 ,the question naturally arises1 if it is possible to construct filters satisfactorily without any retaining walls1 why incur unnecessary expense in providing walls8 ,the answer is that clinker is not universally adopted as a filtering material1 and that the strength of circular walls is not sufficiently taken into consideration4 ,the thickness of the wall will naturally depend upon its height1 but assuming this to be #f feet1 and that the wall is in all cases carried down to a solid foundation1 the extreme thickness that would be needed is probably #ah inches at the bottom and #i inches at the top1 as ,fig4 #gb4 ,as a general rule1 however1 it will probably be found quite sufficient to construct the wall of brickwork in cement1 with the lower half #ad inches and the upper half #i inches in thickness4 ,in a large number of the most recently constructed filters1 the walls have been omitted altogether when clinker has been used for the filter4 ,large pieces of this material have been selected1 and carefully packed in the form of a dry rubble wall with perfect success1 even when laid with a batter on the outside of as little as #a in #f or even #a in #h4 ,it is obvious that this method of construction needs special care and supervision1 especially in providing a rough kind of bond between the different layers1 if it is to be successful4 ,a rough idea of this method is given in ,fig4 #gc4 ,as a kind of happy medium between this system and a wall to the full height of the filter1 a dwarf wall has been adopted in a number of cases1 and notably by ,messrs4 ,willcox and ,raikes1 ,civil ,engineers1 who have also designed a special form of coping1 made in fire-clay or terra-cotta1 as shown in ,fig4 #gd4 ,again1 in several places where suitable local stone1 or stones and bricks resulting from the demolition of old houses or walls1 was available at a cheap rate1 these materials have been utilised to form dry rubble walls1 similar in construction to the clinker walls illustrated in ,fig4 #gc4 ,illustration3 ,,fig4 #gb4 ,illustration3 ,,fig4 #gc4 ,occasionally the walls of filters are carried up several feet above the surface of the filter with the idea of forming a screen to protect the revolving sprinklers from the influence of wind4 ,it is1 however1 obvious that these measures can only have an effect upon the outer ends of the revolving arms1 and1 as the action of the revolving sprinklers is only affected by wind when the head of sewage by which they are driven is at its minimum and the force of the wind is simultaneously at its maximum1 the necessity for windscreens seldom arises4 ,in actual practice1 with an average head of sewage1 no real difficulty is caused by wind4 ,illustration3 ,,fig4 #gd4 ,so far1 it has been assumed that the walls and floors of the filters can be constructed upon solid ground4 ,unfortunately this is not always possible4 ,if the subsoil is of an unsubstantial nature it is advisable to lay the floor of a suitable thickness and diameter1 so that the wall may be built upon the floor itself1 and thus distribute the load over as large an area as possible4 ,in some cases the levels necessitate the raising of the filter floor above the surface of the surrounding ground4 ,under these circumstances the footings of the walls should be carried down to solid ground1 and no reliance whatever should be placed upon made-up ground even to carry the floor alone4 ,the outer edge of the floor should be supported by the footings of the wall1 and the remainder carried upon piers or cross-walls of brickwork1 concrete or masonry1 extended down to solid ground4 ,the piers or cross-walls should be sufficient in number to support the floor with safety4 ,a smaller number may be used if steel joists are provided between them to take the weight of the floor and filter1 or the whole floor may be of a properly designed reinforced concrete construction1 supported at the circumference on the footings of the outer wall and at the centre on a substantial pier of concrete carried down to solid ground1 with intermediate piers if the diameter of the filter is excessive4 ,planning of ,filters4--,the preceding notes with regard to floors1 sub-drainage and walls1 apply generally to all filters1 whether they are for revolving or travelling distributors or for sprays or fixed troughs4 ,the most suitable plan for travelling distributors is naturally rectangular1 but where more than one such filter is required it will be found economical to arrange them in pairs1 with a central supply channel feeding two distributors1 one on each side4 ,this applies equally to other types of fixed distributors1 but care should be taken to divide the total area into reasonable units4 ,in all except the smallest schemes 7which should consist of not less than two units7 it will be found that three1 or multiples of three1 units form a very convenient method of arrangement4 ,this suggestion with regard to the subdivision of the total area applies to filters for revolving distributors1 so far as their number is concerned1 but there are several methods of arranging the area of the filters themselves4 ,when the filters are separated from one another they may be placed in regular order of one kind or another if the site is uniformly flat1 or irregularly to suit the contour of the ground if the site is uneven4 ,it has been considered an objection to the use of circular filters that even if they are placed close together a considerable amount of space is rendered useless4 ,there may be some justification for this objection in cases where the area of the site is limited4 ,on the other hand1 the objection has been overcome by arranging the total filter area on one common floor1 fixing the revolving distributors so that the circumferences of the areas they cover meet where possible1 and leaving the spaces not covered by the distributors free of material to provide some lateral aeration for whatever it is worth1 or as an alternative to provide a convenient position for chambers to receive the effluent from the contiguous filters4 ,this arrangement is illustrated in ,fig4 #ge4 ,if other arrangements are made for the discharge of the effluent1 then the spaces in question may be filled with material and utilised as filters by fixing smaller suitable distributors1 as ,fig4 #gg4 ,this has been done at ,kingston-on-,thames in converting existing rectangular contact beds into percolating filters1 while at ,darwen1 ,lancs1 the intermediate spaces not covered by the revolving distributors are utilised as filters and the distribution effected by means of fixed sprays4 ,illustration3 ,,fig4 #ge4 ,illustration3 ,,fig4 #gf4 ,illustration3 ,,fig4 #gg4 ,in other cases the filters for revolving distributors have been constructed octagonal in plan instead of circular1 as shown in ,fig4 #gf4 ,by constructing suitable retaining walls the whole scheme presents a very good appearance1 and the intervening spaces can be utilised for effluent chambers or as filters with smaller distributors1 as previously described1 and practically the whole area is thus utilised4 ,filtering ,material4--,on this subject there exists a great diversity of opinion4 ,some engineers are satisfied to use any kind of material which will not disintegrate rapidly1 while others pin their faith to one particular kind4 ,again1 the grading of the material is a matter upon which it is seldom possible to find two engineers in complete agreement4 ,the opinion is frequently expressed that true economy consists in utilising local material as far as possible1 sometimes even to the extent of adopting a local product1 even though it is admittedly not so good as some other material which may cost slightly more for carriage from a distance4 ,undoubtedly the first consideration is to secure a material which will not disintegrate1 but this is not the only essential qualification4 ,the author has had many opportunities of observing the results obtained from various materials1 and1 for dealing with an average sewage1 he has never seen a better material than hard-burnt vitrified furnace clinker4 ,this material1 of the proper kind1 is practically equal to stone or gravel in its ability to withstand the various influences which tend to cause disintegration1 but it possesses the advantage over stone and gravel of having numerous cavities1 which apparently form the most suitable means of assisting the development of the bacterial gelatinous growth1 which appears to be the essential factor in causing the deposition of the organic matters in suspension and in solution in the tank effluent4 ,it would seem as if the smooth surfaces of gravel or broken stone cannot retain this growth1 and that it is washed away as soon as it begins to form4 ,it is true that excellent effluents are obtained from filters of gravel or stone1 but1 so far as the author is aware1 only by providing a larger cubic capacity of filter than would be required if proper clinker were used4 ,it is thus questionable whether the lower cost of local stone or gravel does1 in fact1 result in ultimate economy1 if a smaller quantity of the right kind of clinker1 at a slightly higher price per cubic yard1 will secure the same result4 ,it will be noticed that stress is laid upon the necessity of using the right kind of clinker4 ,this is intentional1 as the word 8clinker0 appears to cover a large variety of material4 ,house refuse1 cinders1 and over-burnt bricks1 as well as the products of refuse destructors1 are all considered as 8clinker10 especially in cases where a contractor finds he has taken a very low price for filter material in making up his tender4 ,in the author's opinion1 the only kind of clinker1 indeed the only kind of material1 which should be used for percolating filters is the extremely hard clinker from boiler furnaces1 more or less vitrified throughout1 and not only of irregular shape1 with a rough surface1 but possessing numerous cavities on all sides4 ,clinker of this type is occasionally to be obtained from destructor furnaces1 but it depends upon the character of the original refuse1 and probably to some extent upon the method of stoking4 ,in any case it necessitates the exercise of experienced judgment and discrimination in selection1 and in some cases destructor clinker is so soft1 and so evidently certain to undergo rapid disintegration1 that it should be rejected at all costs4 ,among other materials which are used for percolating filters in various parts of the country are coal1 broken saggars1 stone of various kinds1 including granite1 gravel1 broken bricks1 coke1 cinders1 coke-breeze1 and slag from ironworks1 but in the author's opinion none of these are so satisfactory as the right kind of clinker described above4 ,grading of ,filtering ,material4--,there is probably as much1 if not more1 diversity of opinion on this point as in the matter of the kind of material most suitable for filters4 ,the sizes in actual use vary from inch to #c inches and even #f inches4 ,some engineers stipulate for a uniform grade throughout the filter1 others prefer to have different grades at different depths1 while still others are satisfied to allow small and large pieces to be mixed together indiscriminately4 ,in the author's opinion the last mentioned method is the least satisfactory of all4 ,one of the essential factors in obtaining the maximum efficiency from percolating filters is a free passage for air to enter into all parts of the filter4 ,this can only be secured if the interstices between the pieces of material are kept clear at all times1 but when small and large pieces are mixed together1 the small have a natural tendency to fall into the spaces between the large pieces and thus choke them4 ,even if this were not of importance1 the usual methods of filling a filter do not permit of the uniform distribution of the finer particles among the larger1 so that the usual result is that some portions of the filter consist almost entirely of fine and others of coarse material1 and the results must of necessity be unequal4 ,on the face of it1 the division of a filter into layers1 each consisting of a different grade of material ranging from coarse at the bottom to fine at the top1 would appear to be an excellent idea1 but it is only those who have attempted to put this idea into practice who appreciate the extreme difficulty of carrying it out4 ,with the exception of very small filters1 where constant supervision and an unlimited amount of labour is available1 it will be found impracticable under ordinary circumstances4 ,there still remains the first-mentioned alternative1 viz4 to have the material as nearly as possible of a uniform grade throughout the filter4 ,whether the grade should be fine1 medium or coarse1 will depend upon the strength and character of the liquid to be treated1 but in either case the best practice from all points of view is1 in the opinion of the author1 to provide all of a uniform grade4 ,in making this statement1 it is assumed that there will be a layer about #f inches deep of coarser material all over the floor1 as this is necessary to prevent the finer grade above it being washed through in the effluent or choking the apertures in the sub-drains4 ,in some cases also a modification is adopted in providing the top layer1 about #f inches to #ab inches in depth1 of finer material than the bulk of the filter1 in order to arrest any suspended solids that may be present in the tank liquor1 upon the surface of the filter1 from which they can be more readily removed than if they were allowed to enter the filter4 ,on the other hand1 some prefer to allow these solids to enter the filter1 but to provide ample clear interstices and sub-drainage1 so that these solids after treatment in the filter may be washed out as humus or 8converted products0 in the effluent1 from which they are easily removed by settlement in suitable tanks to be described later4 ,methods of ,distribution4--,the question of distribution is the most important factor in the successful operation of percolating filters4 ,at first it was considered sufficient simply to spread the liquid as evenly as possible over the surface of the filter by any convenient method4 ,gradually improvements in methods were introduced with varying results1 and at the present time a large number of different appliances are to be found in actual use1 some producing jets1 others a fine spray1 and others again what is termed a 8thin film40 ,all of these have their advocates1 and all undoubtedly can be made to give satisfactory results4 ,one of the essential requirements of any method is that it shall give even distribution per unit of superficial area of the filter4 ,whether the jet or the spray or the thin film is the most efficient in this respect is a matter of opinion4 ,on this question of distribution1 one of the most important points to be taken into consideration in forming an opinion as to the best method to adopt is1 what happens after the liquid is discharged on to the surface of the filter8 ,what happens beneath the surface1 in the body of the filter8 ,the generally-accepted theory is that the liquid trickles slowly over the surface of the separate pieces of the material1 dropping from one to the other and ultimately falling to the floor of the filter1 and thence flowing to the effluent drain4 ,no definite investigations into this question appear to have been made until the year #aiji1 when a series of extremely interesting experiments were carried out by ,mr4 ,w4 ,gavin ,taylor1 ,m4 ,am4 ,soc4 ,c4,e41 ,resident ,engineer1 ,sewage ,disposal ,works1 ,waterbury1 ,conn41 ,u4,s4,a4 ,the results of these tests were published in the 8,engineering ,record0 of ,june #e1 #aiji1 and illustrated by excellent graphic tables1 which show that1 8,percolating liquids were more equally diffused in the fine material than in the coarse2 that the plotted curves of diffusion approximate parabolas having their apexes at the surface of the filter material2 and that1 in general1 about one-half of the total lateral movement taking place within a #f foot depth was effected within the uppermost foot of material40 ,these observations apply to the effect produced by single drops applied at the surface4 ,further tests made to ascertain the effect of distribution on several adjacent points at the surface of the filter demonstrated that1 8,the liquid from each point of application spread out through the material in the normal cone of diffusion1 until its cone was intersected by that from an adjacent point of application2 that there the two or many liquid films united1 as tributary sources1 into minute streams which interrupted1 to a considerable degree1 the continuance of diffusion and tended to descend through the remaining material at a higher velocity and along lines of least resistance4 ,the streaming tendency increased rapidly as the rates of application were made greater40 ,among the final conclusions drawn from these tests the most important is that1 8,the desideratum in the application of sewage to percolating filters is to attain perfection in aerial distribution1 and that a high efficiency in sub-surface distribution is fostered by a slow continuous rate of application rather than by an intermittent application at a higher rate40 ,this last sentence fully confirms the author's own opinion with regard to the use of dosing tanks which are dealt with later under the heading 8,methods of ,feeding ,percolating ,filters40 ,in the following pages a number of the many appliances which have been introduced for distributing tank effluents upon percolating filters are illustrated and described in detail1 the various types being grouped under separate headings4 ,illustration3 ,sectional ,elevation on ,line ,a4,b4 ,sectional ,plan on ,line ,c4,d4 ,,fig4 #gh4--8,,open0 ,,type1 ,,candy-,,whittaker ,,sprinkler4 ,illustration3 ,,fig4 #gi4--8;,,closed0 ,,type1 ,,candy-,,whittaker ,,sprinkler4 ,automatic ,revolving ,distributors4--,one of the first1 if not the first1 of the revolving distributors for percolating filters was the 8,candy-,whittaker0 sprinkler in its original form4 ,this is supplied by the ,patent ,automatic ,sewage ,distributors1 ,ltd4 ,it is now made in three different forms3 the 8,open0 type1 the 8,enclosed0 type1 and the 8,buoyant0 distributor1 as shown in ,figs4 #gh1 #gi1 and #hj4 ,the most prominent feature of these sprinklers is the mercury seal joint1 for which it is claimed that it gives an absolutely watertight and frictionless joint1 that it cannot freeze1 and that no renewal of the mercury is required4 ,it is stated that the use of the patent 8check-ring0 in combination with the mercury seal prevents any loss of the mercury1 no matter what the head may be4 ,another feature is that the ball-bearings are moisture-proof1 due to the special methods of construction4 ,in addition to the above1 the makers point to the special value of their compensating arms system1 by means of which their distributors will work continuously with a very small volume of sewage and still be capable of dealing with any larger volume of sewage that may be required4 ,the names of the 8,open0 and 8,enclosed0 types are self-explanatory1 but the 8,buoyant0 type is specially designed to reduce the friction on the bearings4 ,the revolving portion is supported by a float or buoy in the form of a cylindrical tank1 which floats in a small chamber at the centre of the filter4 ,the removal of all weight friction on this distributor reduces the power required to rotate it to the minimum4 ,illustration3 ,,fig4 #hj4--8;,,buoyant0 ,,type1 ,,candy-,,whittaker ,,sprinkler4 ,another make of revolving distributor is well-known as the 8,cresset40 ,this is manufactured by ,messrs4 ,adams ,hydraulics1 ,ltd41 and is illustrated in ,fig4 #ha4 ,in this case the special feature is the joint between the revolving and fixed portions of the apparatus4 ,it consists of a simple air-lock1 formed by a cushion of air between two water columns4 ,this is clearly seen in the illustration4 ,it is obvious that this is an absolutely frictionless joint1 so that there is no loss of head4 ,it also has the effect of removing the strain to which the overhead ball-bearings are generally subject1 so that the revolving body swings freely in the true vertical line from the cross head above4 ,another point is that no expense is involved1 and very little trouble is incurred1 in renewing this joint whenever it may be found necessary1 but it has been maintained in perfect condition without requiring renewal for very long periods4 ,special means are provided for removing and replacing the ball-bearings in the cross-head without dismantling the distributor4 ,another type of distributor manufactured by ,messrs4 ,adams ,hydraulics1 ,ltd41 is their 8,sypho-,jet10 as shown in ,fig4 #hb4 ,as its name implies1 it is siphonic in action1 and combines the functions of a sprinkler and intermitting valve in one apparatus4 ,it may either be used in connection with a dosing tank or connected direct to the settling tank1 from which it draws off a certain depth of water every time it fills to a certain height4 ,illustration3 ,,fig4 #ha4--8;,,cresset0 ,,revolving ,,distributor4 ,illustration3 ,,fig4 #hb4--8,,sypho-,,jet0 ,,revolving ,,distributor4 ,two types of revolving sprinklers are manufactured by ,messrs4 ,mather and ,platt1 ,ltd4 ,these are illustrated in ,figs4 #hc and #hd4 ,the special feature claimed for the 8,pipe ,arm0 distributor is the overflow centre1 as this eliminates the use of joints or seals4 ,another point of interest in connection with this apparatus is that there are two sets of ball-bearings at the head1 one to take the weight of the revolving portion1 the other to take lateral movement4 ,in addition there is a set of roller-bearings at the centre1 which are arranged to prevent lateral movement1 and they can be adjusted to take up any wear that may occur4 ,the 8,open-trough0 type1 ,fig4 #hd1 is provided with a special turbine arrangement at the centre1 which it is claimed gives an immediate motion when the sewage is turned on4 ,the distributing troughs being open assist in aerating the liquid1 and as it is possible to provide holes in the bottom of the troughs these are able to drain completely dry1 and can also easily be cleaned4 ,this apparatus is provided with ball and roller bearings1 as described in connection with the 8,pipe ,arm0 type mentioned above4 ,illustration3 ,,fig4 #hc4--,,pipe-,,arm ,,distributor4 ,illustration3 ,,fig4 #hd4--,,trough-,,arm ,,distributor4 ,messrs4 ,george ,jennings1 ,ltd41 manufacture a revolving distributor1 the special feature of which is that the sewage is delivered from the central fixed column to the revolving tank1 to which the arms are attached1 by means of a syphon formed in the central column itself1 but this syphon is disconnected from the supply pipe by a fixed cylinder and port-holes1 which make the syphon independent of the pressure at the inlet to the supply pipe outside the filter bed4 ,the pressure acting upon the syphon is therefore the atmospheric pressure applied direct to the surface of the liquid in the fixed cylinder1 thus operating without any loss of head4 ,in addition to the ordinary overhead ball-bearings1 a gun-metal bearing is provided to check any excessive lateral movement4 ,the syphon described above when once started remains sealed1 as the outlets are trapped by the liquid at the bottom of the revolving cylinder1 and as the top lip of the revolving cylinder is arranged to be #f inches above the top water level in the tanks1 any flooding at the centre of the bed by the liquid overflowing at this point is impossible 7see ,fig4 #he74 ,when required to deal with fluctuating flows this sprinkler can be fitted with compensating arms4 ,messrs4 ,whitehead and ,poole manufacture a revolving sprinkler1 as shown in ,fig4 #hf1 in which a float is used to carry the weight of the rotating parts1 so that wear and tear and friction are reduced to the minimum4 ,the chamber containing the float is completely closed1 and this is below the surface of the filtering material1 so that they are not affected by frost4 ,in this sprinkler the joint between the fixed and rotating parts is made by utilising a little of the buoyancy of the float to form an upward bearing at the neck of the float chamber4 ,it is claimed that this joint is perfectly watertight1 with the minimum of friction4 ,illustration3 ,,fig4 #he4--,,revolving ,,distributor4 ,illustration3 ,,fig4 #hf4--;,,buoyant ,,revolving ,,sprinkler4 ,illustration3 ,,fig4 #hg4--,,revolving ,,distributor4 ,the revolving distributor manufactured by ,messrs4 ,ham1 ,baker and ,co41 ,ltd41 shown in ,fig4 #hg1 consists of a revolving trough to which the distributing pipes are connected4 ,the trough is supported upon ball bearings carried upon a pillar1 and the special feature of the apparatus is that the incoming sewage is delivered into the central trough in such a way that it strikes upon blades fixed in this trough1 and it is claimed that in this way full advantage of the initial head of sewage is obtained4 ,by this means also no special joint is required between the fixed and revolving parts4 ,a special method of gaining access to the ball-bearings for inspection and cleaning is provided4 ,in connection with this distributor the makers supply an automatic cleaning gear for the spray holes1 ,fig4 #hh4 ,this consists of a rocking bar attached to each arm of the distributor and provided with a number of small fingers or pickers1 one opposite to each hole4 ,an arm or a lever attached to the rocking bar1 and suspended from same to within a short distance of the surface of the filter1 comes into contact with a block of wood or other material fixed in the filter itself at each revolution1 and thus causes a movement of the rocking bar which actuates the finger points and causes them to pass in and out of the spray holes in the arms4 ,by this means any obstruction is removed and forced out by the pressure of water within the arm1 and the holes are kept free4 ,illustration3 ,,fig4 #hh4--;,,cleaning ,,gear ,,for ,,spray ,,holes4 ,the 8,facile0 rotary distributor shown in ,fig4 #hi is manufactured by ,messrs4 ,w4 ,e4 ,farrer1 ,ltd4 ,the special advantage claimed for this distributor is that it has no joint1 so that there is no friction to overcome beyond that in the ball-race1 upon which the whole weight of the revolving portion is supported4 ,it is provided with a syphonic attachment to the central column1 and thus acts as a self-dosing distributor1 and1 if desired1 can be connected direct to the septic tank4 ,a patent gauging tube is fitted1 so that the volume of the dose may be gauged whether it is fed from the dosing chamber in the ordinary way or direct from the septic tank4 ,access is provided to all parts1 and the ball-race can be removed without dismantling the apparatus4 ,illustration3 ,,fig4 #hi4--8;,,facile0 ,,revolving ,,distributor4 ,illustration3 ,,fig4 #ij4--,,the 8,,carlton ,,rotor0 ,,distributor4 ,among the later types of revolving sprinklers is the 8,carlton ,rotor0 distributor1 ,fig4 #ij1 manufactured by the ,carlton ,engineering ,company4 ,this is specially designed to obviate the use of a dosing tank1 to work satisfactorily with any variation of flow1 and to prevent all possibility of choking4 ,it is claimed that these advantages are secured by the use of a special water-wheel which rotates round the central column on an inclined plane4 ,the sewage is delivered to this water-wheel by means of a bend connected to the central column4 ,as each section of the water-wheel is filled1 it rotates and delivers its contents into an annular trough1 to which the distributing arms are attached4 ,these are1 however1 not perforated with spray holes1 but are provided with small bends on the top of the arms1 which deliver the sewage into distributing troughs fitted with baffle plates4 ,these baffle plates are so arranged that the sewage is delivered on to the surface of the filter in a thin film and at a uniform rate over the whole surface4 ,illustration3 ,,fig4 #ia4 ,illustration3 ,,fig4 #ib4--,,the 8,,carlton0 ,,distributor4 ,a novel apparatus for the purpose of providing an automatic method of cleaning the orifices of the arms of revolving or travelling distributors is shown in ,fig4 #ia4 ,this is supplied by the ,carlton ,engineering ,company1 in connection with their ordinary type of revolving distributor1 also shown in ,fig4 #ib4 ,in the distributing arm ,b apertures are made in the form of elongated slots ,a1 each slot having a brass cleaning blade ,e inserted4 ,these blades are carried on brackets fixed by a set-screw ,d1 on to a reciprocating rod or tube ,c1 mounted on runners ,f4 ,two bevel wheels ,g are strapped on to the arm1 and are connected by an eccentric rod to the reciprocating rod ,c4 ,at every revolution which the distributing arm makes1 the bevel gearing ,g comes in contact with the stop ,h1 causing a partial revolution of the gearing4 ,this in turn causes the backward and forward motion of the cleaning blades in the apertures4 ,the apertures are thus kept entirely free from grit or any other solid matter1 and the flow is broken up into a fine spray4 ,illustration3 ,,fig4 #ic4--8,,simplex0 ,,revolving ,,distributor4 ,the 8,simplex0 revolving distributor is manufactured by the ,ames ,crosta ,sanitary ,engineering ,company1 ,ltd41 and illustrated in ,fig4 #ic4 ,this sprinkler revolves on a ball-bearing which runs in a bath of solid grease1 and is protected from moisture and dust by means of special washers4 ,the whole of the weight is carried from the top of the pillar1 no bearing being submerged in the sewage4 ,the seal is arranged by means of two gun-metal rings with special annular grooves turned in them2 the top ring is carried from the revolving bucket by means of a rubber or copper washer1 thus the ring carries no part of the weight of the apparatus1 and is free to compensate for any oscillation4 ,rollers running on ball-bearings are placed under the bucket1 and these take up side movement due to wind and other causes4 ,the revolving arms are provided with a special cap at the ends1 which can be removed by a quarter turn to enable the arms to be cleaned4 ,there is no head lost1 as the level of water in the bucket is equal to the head in the supply chamber or channel4 ,the apparatus is not affected by frost1 and is remarkably sensitive1 as #b inch head of water above the holes in the arms will start the apparatus in motion4 ,illustration3 ,,fig4 #id4--,,revolving ,,sprinkler 7,burn and ,brown's patent74 ,messrs4 ,burn ,bros4 manufacture a revolving sprinkler1 8,burn and ,brown's ,patent10 shown in ,fig4 #id1 which has one or two special features4 ,these consist of a self-regulating apparatus for dealing with the variation of the flow of sewage and at the same time cleaning the orifices4 ,a shaft carried on each of the arms1 and mounted on suitable bearings1 is provided with tapered fingers fixed in a position corresponding to the holes in the arms4 ,by means of a float in the circular revolving tank connected to a simple lever the shafts on the arms are given a slight movement1 which causes the fingers to enter the orifices in the arms as the flow decreases1 and to be withdrawn as the flow increases4 ,the result is that the orifices are enlarged or reduced as the flow varies1 and the movement of the tapered fingers tends to make the orifices self-cleansing4 ,it is claimed for this distributor1 that it can be made to deal with any variation in flow of sewage up to #f volumes1 with a maximum head of less than #ah inches above the surface of the material of the filter4 ,a new type of automatic revolving sprinkler is the 8,hodgson0 overflow type1 manufactured by ,messrs4 ,george ,kent1 ,ltd4 ,as will be seen from the illustration1 ,fig4 #ie1 the sewage passes first into a feed chamber attached to the central column1 from which it flows into the distributing chamber ,d1 to which the arms are attached4 ,it is claimed that by use of the weirs ,w in the distributing chamber1 a uniform speed of rotation and consequently a uniform distribution1 is secured4 ,the ball-bearing upon which the rotating portion is carried is stated to take both the side and end friction4 ,the revolving distributors previously described are all constructed on the ,barker's ,mill principle1 to some extent if not entirely4 ,the ,fiddian type of distributor1 supplied by ,messrs4 ,birch ,killon and ,co41 and illustrated ,fig4 #if1 is based upon an entirely different principle4 ,it consists of an elongated water-wheel1 which revolves around a circular filter4 ,it is pivoted at the centre of the filter upon the supply pipe1 and the outer end of the distributor is carried upon a rail track4 ,in the case of large filters1 from #gj feet to #aaj feet diameter1 two rail tracks are used4 ,the liquid passes through the supply pipe and is delivered into the buckets of the water-wheel1 from which it falls in the form of a film1 so that the water-wheel not only drives itself over the filter by means of the weight of the liquid1 but it also distributes the liquid which drives it4 ,a very small quantity is sufficient to start the distributor and keep it in motion1 the head required1 measured from the surface of the filter1 being about #ah inches4 ,the buckets are provided with graduated weirs1 the width of which is proportionate to its distance from the centre of the filter4 ,by this means uniformity of distribution is secured4 ,it is claimed that as there are no small holes to be choked1 the apparatus can be employed for all kinds of liquid with the minimum of attention1 and that it does not require any dosing apparatus4 ,illustration3 ,,fig4 #ie4--8;,,hodgson0 ,,revolving ,,sprinkler4 ,illustration3 ,,fig4 #if4--;,,fiddian ,,revolving ,,distributor4 ,power-driven ,revolving ,distributors4--,one of the first revolving distributors in which it was decided to adopt power to drive it independent of the sewage1 was the 8,scott-,moncrieff and ,alliott0 distributor1 manufactured by ,messrs4 ,manlove1 ,alliott and ,co41 ,ltd41 and erected at the ,birmingham ,sewage ,farm for ,mr4 ,j4 ,d4 ,watson4 ,in this case a horizontal arm is attached to and pivoted upon the vertical stand-pipe in the centre of the filter which is connected to the supply pipe4 ,the outer end of the horizontal arm is carried by a rail1 and is fitted with an oil engine which travels along on the outer rail on the end of the arm4 ,the rotating arm consists of a large main trough or carrier into which the sewage from the central stand-pipe is delivered1 and on one side of the main trough is fitted a row of small troughs1 each of which is supplied with sewage from the main carrier through a porthole specially proportioned to the volume of sewage to be discharged from the trough and to its distance from the centre of the bed4 ,by this means uniform distribution is secured over the whole area of the filter4 ,from each of the small troughs the sewage flows over the edges of the trough1 and thence1 trickling down the outside of the trough1 is discharged in a row of fine rain-like columns upon the filter4 ,it is claimed for this distributor that absolute uniformity of distribution is secured1 that it will work equally well with any volume1 that there are no holes to become choked1 that it requires the minimum of supervision1 and that it will deal with any variation up to #c times ,d4,w4,f4 without attention 7,fig4 #ig74 ,illustration3 ,,fig4 #ig4--,,scott-,,moncrieff ,,power-,,driven ,,revolving ,,distributor4 ,in the 8,hartley0 circular power-driven distributor1 the apparatus 7manufactured by ,messrs4 ,hartley1 ,causton and ,richmond1 and shown in ,fig4 #ih71 is arranged in a form similar to that used in connection with the ,barker's mill type of distributor1 with this difference1 that it is driven by an electric motor attached to the end of one of the arms1 which is used as the distributing arm2 and the arm on the opposite side is the balancing arm to counteract the dead weight of the distributing arm and act as a balance against wind pressure4 ,the current is brought to the distributor by an overhead cable1 connected to a revolving contact at the top of the central standard4 ,the method of distribution from the distributing arm is different from the usual type1 as it takes place through a number of sectional distributing pipes ,c 7,fig4 #ii71 which are connected to the main tube ,h4 ,these are arranged in echelon1 so that by opening the covers ,p ,p a cap or cleaning rod may be passed through each tube from end to end4 ,each sectional distributing tube1 ,c1 is suspended from the main tube by an attachment ,d4 ,this attachment carries a screw1 ,g1 by which is regulated a valve shown open at ,e and closed at ,e#b4 ,the flow may be increased or decreased to any extent1 or stopped altogether1 by this valve4 ,each space between the dotted lines on the plan is covered by one sectional tube1 and the sewage flow can be increased or decreased1 or stopped upon each section4 ,the spray nozzles are of a special type1 and by use of the deflection or spray plates ,m1 a smaller number of spray holes or jets are required1 so that they can be made larger1 and they are thus not so easily choked4 ,among the advantages claimed for this distributor are the following4 ,that it can be regulated to work with any variation in the volume1 from the smallest quantity to #b million gallons per acre per day1 without increasing the consumption of power4 ,separate sections of the filter may be removed or rested entirely by adjusting the valves ,g4 ,the distributor can work with any head of sewage from #f inches to #f feet1 or more if desired4 ,it is not affected in any way by wind pressure2 and as the balancing arm empties at the same time as the distributing arm1 it is always in balance4 ,the horse-power required to drive it is very little1 less than half horse-power per acre4 ,the rate of distribution on any of the sections of the filter can be varied from #ej to #djj gallons per yard per day4 ,illustration3 ,,fig4 #ih4--,,power-,,driven ,,revolving ,,distributor4 ,illustration3 ,,fig4 #ii4--;,,details ,,of ,,distributing ,,arm4 7,see ,,fig4 #ih47 ,this type of distributor was first erected at the ,hanley ,sewage ,works in #aijb1 in order to comply with ,messrs4 ,willcox and ,raikes' specification fora power-driven distributor suitable for a large circular filter1 on which a ,scott-,moncrieff distributor was previously employed4 ,illustration3 ,,fig4 #ii;,a4--,,view ,,of ,,hartley ,,causton ,,and ,,richmond',s ,,power-,,driven ,,revolving ,,distributor ,,in ,,operation4 ,a somewhat similar type of distributor is the 8,adams-,cutler0 ,fig4 #ajj1 manufactured by ,messrs4 ,adams ,hydraulics1 ,ltd4 ,in this case the distribution is from spray holes in the pipe arms in the same way as the ordinary ,barker's ,mill type of distributor1 but instead of relying upon the motive power due to the head of sewage1 the distributor is operated by a rope drive2 and where there are a number of distributors in one installation1 each of them is operated by a cross-drive taken from a main drive rope1 so that any one or more can be cut out of the circuit or controlled1 or the speed varied as may be required4 ,it is claimed that a very small amount of power is required to operate a revolving distributor1 and the ease with which it is carried upon a central column1 are arguments in favour of the revolving over the rectangular types where absolute control is essential and a natural working head is not available4 ,illustration3 ,,fig4 #ajj4--8;,,adams-,,cutler0 ,,power-,,driven ,,revolving ,,distributor4 ,messrs4 ,mather and ,platt1 ,ltd41 also manufacture an electrically-driven revolving distributor of the ,open ,trough type1 as shown in ,fig4 #aja4 ,this machine is of special design1 and particularly suited for large diameter beds4 ,the troughs are similar to those of the ordinary type of distributor previously mentioned1 but are supported on the ,warren ,girder principle4 ,there are four pipe arms1 the end of each being fitted with a special carriage running on rails fixed outside the bed at the floor level4 ,on one of the carriages an electric motor is fixed and connected to the rail wheels by means of chain drives4 ,the current is transferred to the motor from the main at the top of the central1 pole of the distributor by means of slip rings4 ,illustration3 ,,fig4 #aja4--,,power-,,driven ,,revolving ,,distributor4 ,automatic ,travelling ,distributors4--,there are several types of these on the market at present4 ,the first is manufactured by ,messrs4 ,birch ,killon and ,co41 ,fig4 #ajb1 and is constructed on the ,fiddian water-wheel principle4 ,the design is similar to that described in connection with the automatic revolving distributor1 but it involves two rail tracks supported on walls or piers on each side of the filter4 ,the head required for this type is about #b feet from the surface of the filter to the top water level in the carrier1 and the distributor is fitted with a syphon which feeds it from the carrier or trough4 ,in large schemes the trough is placed along the centre of the filter1 and supplies a separate distributor on each side4 ,illustration3 ,,fig4 #ajb4--;,,fiddian ,,travelling ,,distributor4 ,another type is manufactured by ,messrs4 ,ames ,crosta ,sanitary ,engineering ,company1 as shown in ,fig4 #ajc4 ,this sprinkler can be adapted to existing contact beds4 ,it is carried from the walls of the central channel in cantilever form1 no other bearing or rails being required4 ,on each side of the machine a hopper is carried in which water-wheels revolve4 ,the water in its passage from the feed channel to the distributing arms is conveyed on to the water-wheels1 and the power generated there is transmitted by means of a chain drive to the wheels of the carriage1 and thus the whole apparatus is moved along the beds4 ,when the machine nears the end of the bed a reversing lever comes in contact with a buffer1 and by this means the direction of motion is changed1 and the machine travels backwards along the bed4 ,two distributing arms are carried on each side of the apparatus1 one feeding half the bed in one direction and the other feeding the remaining portion of the bed in the opposite direction1 thus giving a regular intermittent feed to the bed4 ,a great advantage of this class of machine is that the whole of the machine is supported from the central channel1 and as the wheels are close together1 the long lengths of shafts with their risk of twisting1 retarding and wearing are dispensed with4 ,illustration3 ,,fig4 #ajc4--,,travelling ,,distributor4 ,messrs4 ,ham1 ,baker and ,co41 ,ltd41 have for some time supplied an automatic travelling distributor4 ,this is illustrated in ,fig4 #ajd1 from which it will be seen that it consists of a water-wheel mounted on rollers and divided into sections composed of a number of buckets4 ,the sewage is delivered through a syphon and patent reversing valve1 in such a way that alternate sections only of the filter bed receive sewage in each direction of travel1 thereby insuring equal inter-delivery periods4 ,illustration3 ,,fig4 #ajd4-,,travelling ,,distributor4 ,illustration3 ,,fig4 #aje4--8;,,hanley0 ,,power-,,driven ,,travelling ,,distributor4 ,power ,driven ,travelling ,distributors4--,the well-known ,hanley ,distributor was specially designed by ,messrs4 ,wilcox and ,raikes1 ,civil ,engineers1 for use on their schemes at ,hanley1 ,fenton1 ,ilkeston and elsewhere1 as illustrated1 ,fig4 #aje4 ,the object of this distributor is to ensure intermittent discharge at regular intervals1 and at a predetermined rate1 in the form of a thin film over the surface of fine grade material1 and in order to secure these results it was decided to drive the distributor by electric power rather than depend upon the variable and limited amount of power obtainable from the head of the sewage itself4 ,the distributor consists of a pipe extending across the whole width of the bed and supported on wheels1 so that it may be drawn backwards and forwards by means of the wire rope attached to the centre4 ,the distributing pipe tapers towards the end farthest from the supply trough1 and the sewage is discharged by means of nozzle pipes attached to the flat side of the distributor about #c inches apart1 and connected with it near the top so that the main pipe always remains full4 ,the discharge of the sewage commences and stops along the whole length of the pipe almost simultaneously1 and any sediment lies in the bottom of the main pipe where it cannot obstruct the outlets of the nozzles4 ,the nozzles are about inches in diameter1 and provision is made for cleaning them by removing a plug in the top of each4 ,in order to secure a uniform interval of time between each dose of sewage discharged on to any part of the filter1 the distributors are arranged to discharge when travelling in one direction only1 the valves on the outlets of the feed syphons being automatically turned off and on by means of a lever1 which is actuated by stops fixed at each end of the iron trough or at any intermediate point desired4 ,in this way it is possible to arrange for any portion of the filter to be thrown out of action when necessary for cleaning or repairs4 ,the speed at which the distributor travels may be varied by adjusting the gear wheels attached to the electric motor4 ,at ,hanley it has been found that the best results are obtained when the distributors occupy about #g minutes in making one complete journey1 the filters being #bjj feet long1 so that when the filters are working at the normal rate of #a1jjj1jjj gallons per acre per day1 each dose represents one gallon per square yard4 ,in other words1 the film one-fifth of an inch in thickness is applied #bjj times per day1 and thus a total depth of #dj inches of sewage is distributed over every portion of the filters in operation in #bd hours4 ,the power required to drive the distributors is about #a ,b4,h4,p4 per acre of filter4 ,electric motors are usually adopted1 but small oil or gas engines may be substituted when electric current is not available4 ,the winding drums for the wire ropes are driven by belt gear of the usual type with fast and loose pulleys4 ,the reversal of the drum when the distributor reaches either end of the filter is accomplished by an automatic belt striking gear1 and a float in the supply trough is used to cut out a distributor1 or continue in action at a reduced rate1 when the supply of sewage becomes insufficient to maintain the normal rate of distribution4 ,these distributors are manufactured by ,messrs4 ,blakeborough and ,sons1 and have now been in regular use since #aijb on the ,hanley ,sewage ,disposal ,works1 where the remarkably satisfactory results obtained are largely due to the highly efficient system of distribution on the filters4 ,illustration3 ,,fig4 #ajf4--8,,stoddart0 ,,distributor4 ,illustration3 ,,fig4 #ajg4--8,,stoddart0 ,,distributor4 ,fixed ,distributors4 ,trays and ,troughs4--,one of the best known of the fixed distributors is the 8,stoddart10 as illustrated in ,figs4 #ajf and #ajg4 ,it will be seen that it consists of trays of galvanized sheet iron1 formed into a number of ,v-shaped troughs4 ,the ridges between the troughs are provided with diamond-shaped perforations at frequent intervals1 and in the bottom of the troughs drip points are inserted through holes to project on the under side4 ,the distributing trays are bolted to specially designed supply channels1 connected to a common channel1 and the whole of the troughs are mounted on adjustable chairs 7,f1 ,fig4 #ajf7 carried on tees1 which are in turn supported on concrete or brick piers4 ,as the liquid passes into the ,v-shaped troughs1 it fills them and overflows through the diamond-shaped slots in the ridges and thence trickles down on the under side of each trough and drops off from the drip points on the filter below in the form of rain4 ,it is claimed for this method of distribution that the whole of the available fall is utilised2 that it adapts itself without adjustment to all rates of flow1 however varied1 that the sewage and storm-water may all be treated on the same area1 and that there is a total absence of moving parts4 ,this distributor is supplied by the patentee1 ,mr4 ,f4 ,w4 ,stoddart1 of the ,western ,counties ,laboratories1 ,bristol4 ,another type of fixed distributor is fixed only so far as actual distributing channels are concerned4 ,this is manufactured by ,messrs4 ,w4 ,e4 ,farrer1 ,ltd41 and illustrated in ,fig4 #ajh4 ,the fixed troughs or channels are laid directly over the filter-bed1 and fitted at the inlet end with concentrating chutes which receive the discharges from a double-acting tipping trough1 which is supported at its extreme ends by heavy gun-metal bearings4 ,if it is over #aj feet in length1 an additional support is provided at the centre in the form of a specially designed rocker4 ,the chutes and the channels are provided at the bottom with -inch holes at #c-;inch centres1 through which the sewage is spread on to the surface of the filter1 which is below the underside of the trough4 ,the channels are arranged at #a-;foot centres1 so as to distribute the sewage over the whole area of the bed4 ,by means of the double-acting tipper each half of the filter is dosed alternately1 and suitable periods of aeration are thus provided4 ,this apparatus is suitable for a single small house with #d or #e inmates1 and for larger filters of #fjj square feet in area and upwards4 ,the ,ducat filter is provided with what may be termed a fixed distributor4 ,it consists of a series of small tipping troughs fixed across the filter1 each of which when full tips its contents on to the filter below4 ,the liquid is thus discharged at the same point each time1 but intermittently in small doses4 ,as1 however1 the distributor does not move it is included under this heading4 ,illustration3 ,,fig4 #ajh4--;,,fixed ,,distributor4 ,a different type of fixed distributor is that manufactured by ,messrs4 ,j4 ,blakeborough and ,sons4 ,this apparatus1 patented by ,messrs4 ,haller and ,machell1 ,civil ,engineers1 is used in the triple tank system of sewage treatment4 ,fig4 #aji illustrates the 8,aerat0 type1 which consists of cast-iron channels supported on wrought-iron joists carried upon piers4 ,each length has six orifices on each side1 through which the sewage passes on to small trays provided with radiating grooves on the top and dripping points on the under side at the edge4 ,as the distributors may be fixed within a few inches of the surface of the filter1 very little head is required to operate them4 ,illustration3 ,,fig4 #aji4--;,,fixed ,,distributor4 ,a very ingenious form of fixed distributor1 ,fig4 #aaj1 is supplied by the ,septic ,tank ,company1 ,ltd4 ,from its name1 8,capillary ,trough ,distributor10 it will be observed that during normal and minimum rates of flow1 capillary attraction is utilised to deliver the sewage on the filter in the form of drops4 ,the tank effluent is delivered to each trough distributor over brass ,v-notches1 set in the side of the main channel1 into which the tanks discharge4 ,these ,v-notches are adjustable1 and are set so as to prevent their being tampered with subsequently4 ,the trough distributors are of artificial stone1 true from end to end1 and set level4 ,over both their edges copper wires are fixed1 at intervals of a few inches1 each wire extending from within a short distance of the bottom of the trough channel over the edge and down to the underside of the trough4 ,on a trough being filled the liquid overflows right along the edge1 and is attracted by and runs down the wires1 so that if the flow is at all excessive a little stream will run down each2 on the flow subsiding to the ordinary1 a drop-by-drop delivery commences2 should the flow of sewage cease altogether for any length of time1 the wires will go on dripping until they have drawn off the contents of the trough1 almost to the end of the wires4 ,on a fresh supply of sewage arriving at the installation1 and the troughs refilling to a higher level1 the rate of delivery from the wires will increase until it keeps pace with the flow1 thus ensuring an even distribution on the filter throughout the day4 ,there is no loss of head in connection with this apparatus beyond the depth of the distributing troughs themselves4 ,illustration3 ,,fig4 #aaj4--;,,capillary ,,trough ,,distributor4 ,spray ,jets4--,this type of distribution is not used in many installations in this country1 but it has been adopted in large schemes in the ,u4,s4,a4 ,there are a number of different types1 including those in which the sewage is forced upwards through a nozzle and falls back on the surface of the filter1 and others in which the sewage flows through inverted nozzles1 and each jet impinges upon a fixed cup or disc of metal1 or other material1 and is thus spread out on to the filter4 ,among the former1 one of the simplest types is that manufactured by ,messrs4 ,adams ,hydraulics1 ,ltd41 ,fig4 #aaa1 in which1 by means of a square baffle plate1 provided with suitable grooves1 the spray is forced out in such a manner that it covers a square area of the filter4 ,it is claimed for this that it covers the whole surface and no portion of the filter is wasted1 as in the case of round jets which cover circular areas4 ,the same firm also supply several other types of fixed sprays1 as shown in the illustration4 ,illustration3 ,,fig4 #aaa4--;,,fixed ,,sprays4 ,another type is manufactured by ,messrs4 ,ham1 ,baker and ,co4 ,this is shown in ,fig4 #aab1 from which it will be seen that it can be adapted to any existing installation1 and to standard spigot pipes4 ,each jet being in the form of a stop-valve1 any individual spray may be put out of action when necessary4 ,messrs4 ,w4 ,e4 ,farrer1 ,ltd41 manufacture a type shown in ,fig4 #aac4 ,the special feature of this is a loose disc inside the nozzle1 which oscillates as the sewage passes through1 and so tends to clear away any flocculent matter which may accumulate in the orifice of the nozzle4 ,the sewage itself is delivered from the nozzle in the form of a very fine film1 and it is claimed that by this means any nuisance from smell is reduced to the minimum4 ,illustration3 ,,fig4 #aab4--;,,fixed ,,spray ,,nozzle4 ,illustration3 ,,fig4 #aac4--;,,fixed ,,spray ,,nozzle4 ,messrs4 ,burn ,brothers also manufacture a fixed spray1 ,fig4 #aad1 called the ,burn and ,brown's ,patent 8,whirl0 ,spray4 ,the special feature of this is that it consists of an inverted conical spreader1 provided with vanes revolving on a spindle4 ,the sewage1 as it leaves the nozzle1 impinges upon the face of the cone1 causing it to revolve rapidly and spread the sewage in the form of fine drops4 ,owing to the special construction of the serrated edges of the cone1 the sewage is well distributed over the whole area covered by the spray4 ,illustration3 ,,fig4 #aad4--8,,whirl0 ,,spray ,,nozzle4 ,illustration3 ,,fig4 #aae4--8;,,acme0 ,,spray ,,nozzle4 ,the 8,acme0 type of fixed spray1 manufactured by the ,ames ,crosta ,sanitary ,engineering ,company1 is shown in ,fig4 #aae4 ,the special feature of this spray is that it has a loose metallic cone1 which is provided with a helical groove1 inside the nozzle4 ,this cone rotates as the sewage passes through the nozzle1 and thus gives a maximum spray with a small head4 ,these sprays have a free waterway1 and the rotation of the cone tends to prevent the choking of the orifice4 ,illustration3 ,,fig4 #aaf4--;,,fixed ,,spray ,,jet4 ,a simple form of fixed spray consists of perforated pipes arranged at suitable intervals over the surface of a filter1 and provided with dosing apparatus to give intermittent supply under pressure1 and thus deliver the sewage in the form of jets from the perforations in the pipes4 ,an improved form of this type of distribution is supplied by the ,septic ,tank ,company4 ,this is illustrated in ,fig4 #aaf1 from which it will be seen that orifices in the top of the distributing pipes are fitted with nozzles1 set at an angle of about #de degrees to the vertical4 ,the discharge from these nozzles1 it is claimed1 gives the maximum efficiency of distribution4 ,illustration3 ,,fig4 #aag4--8;,,carlton0 ,,adjustable ,,fixed ,,spray4 ,a self-cleansing spray jet has been brought out by the ,carlton ,engineering ,co4 ,from the illustration1 ,fig4 #aag1 it will be seen that a plug ,b is fitted into the orifice and supported upon a spindle1 which is attached at its lower end to a lever connected to an automatic tipper on the outside of the nozzle4 ,the tipper is fed by the spray from the nozzle1 and as it falls alternately on one side and on the other it raises and lowers the plug ,b in the orifice1 which tends to prevent any clogging1 and also varies the area of the orifice and the rate of discharge1 as well as the area of the filter-surface covered by the spray4 ,a simple type of fixed spray is supplied by ,messrs4 ,george ,kent1 ,ltd41 and is shown in ,fig4 #aah4 ,in this case the liquid issuing from the nozzle impinges upon a curved surface or cone1 by which it is deflected and spread out1 leaving the surface at an angle of #de degrees to the vertical4 ,one of the advantages claimed for this type is that it has no small holes to become clogged4 ,illustration3 ,,fig4 #aah4--;,,fixed ,,spray ,,nozzle4 ,a novel form of this type of apparatus is manufactured by ,messrs4 ,daniel ,adamson and ,co4 ,above the orifice in the nozzle is suspended a revolving deflecting plate 7,fig4 #aai74 ,the vanes of this plate are shaped in such a way that1 as it revolves1 the jet impinges against a different angle every instant4 ,none of the energy is wasted in churning or throttling1 as the plate merely directs the water in such a way that no two drops ever fall twice on exactly the same spot4 ,it is stated that the diameter of the wetted area of the filter surface is more than double the head4 ,illustration3 ,,fig4 #aai4--;,,adamson',s ,,fixed ,,spray4 ,there are a considerable number of other types of nozzles used for fixed sprays4 ,several of these are illustrated in ,fig4 #abj1 where ,a is the type in use at ,salford2 ,b1 the type used at ,birmingham2 ,c1 a nozzle with a double spreader in use at ,waterbury1 ,conn41 ,u4,s4,a42 ,d shows another type in use at ,waterbury1 with a single spreader1 but this is so arranged that it can be adjusted to give a smaller or larger area of orifice4 ,e shows the type adopted at ,columbus1 ,ohio1 ,u4,s4,a4 ,in connection with some elaborate studies of methods of distribution for percolating filters1 which were carried out for the ,sanitary ,research ,laboratory and ,sewage ,experiment ,station of the ,massachusetts ,institute of ,technology1 by ,messrs4 ,winslow1 ,phelps1 ,storey and ,mc,rae1 a special series of investigations were made into the value of what is referred to as the 8gravity method of spraying40 ,this consists in supplying the sewage from troughs or pipes supported above the filter1 and discharging it through orifices on the under side of the pipes or troughs in the form of solid jets1 which are made to impinge upon concave discs fixed near to the surface of the filter4 ,the effect of this impingement is to cause the liquid to splash upwards and outwards in the form of a fine spray1 and1 as a result of a long series of tests with various forms of discs and various heads1 it was found that the best average results were obtained with a concave metal disc #c inches in diameter having a curvature corresponding to a radius of #b inches4 ,with a total head of #d feet and a head of #c feet from disc to the pipe above1 it gave the best results obtained with that total head4 ,with a total head of #f feet and a head of #d feet from disc to supply pipe1 it gave the best results obtained by any of the forms of this type of distribution that were tested4 ,illustration3 ,,fig4 #abj4--;,,fixed ,,spray ,,nozzles4 ,a method of distribution similar to this type of gravity disc spray is manufactured by ,messrs4 ,glenfield and ,kennedy1 ,ltd4 ,the details of this disc1 with the methods of supporting same and the method of supplying the sewage from an overhead pipe1 are shown in ,fig4 #aba4 ,illustration3 ,,fig4 #aba4--;,,gravity ,,disc ,,spray4 ,in connection with sewage disposal works where chemical precipitation has been adopted for preliminary treatment1 the tank effluent has been distributed over fine-grained percolating filters1 by means of dosing tanks discharging comparatively large volumes intermittently over the surface of the filter4 ,in such cases the aim has been to deliver the liquid at such a rate that it would flood the entire surface of the filter in a very short space of time1 and then percolate through and leave the surface free to aerate for as long a period as possible before the next discharge took place4 ,this process involved the use of small filters1 in order that the area to be flooded should not be too large for the liquid to spread over it rapidly1 and the use of very fine material to prevent the liquid from passing through too quickly4 ,among the difficulties encountered by this method were the displacement of the surface layer of the material1 due to the high rate of delivery2 and the labour involved in cleaning the surface of the filter4 ,a further trouble which arises when effluents from septic tanks are treated by this process is the evolution of evil-smelling gases1 which are certain to cause a nuisance if there are any houses in the vicinity4 ,efforts have been made to obviate this difficulty by distributing the sewage through open-jointed or perforated pipes laid a few inches beneath the surface of the filter1 as described later in connection with contact beds 7page #bjj74 ,while this is satisfactory to a certain extent1 especially where the volume to be treated is small1 and the filter capacity is comparatively large1 neither this method1 nor that of flooding the surface of the filter1 can be said to comply with 8the desideratum in the application of sewage to percolating filters10 quoted previously 7page #ajf71 nor do they avoid the difficulties encountered in securing uniform distribution dealt with in the following pages4 ,the defects of these methods of distribution may also have been aggravated by the very optimistic anticipations on the part of the designers of the schemes as to the volume of sewage which could be satisfactorily purified under such conditions4 ,it is1 therefore1 desirable to point out that1 in the event of either of these methods of distribution being adopted1 care should be taken to secure a very high degree of clarification 7reduction of matters in suspension7 in the preliminary tank treatment1 and to provide filters of ample cubic capacity4 ,methods of ,feeding ,percolating ,filters4--,under the heading 8,methods of ,distribution0 7page #ajf71 reference is made to some experiments1 from the results of which the conclusion was drawn that 8a high efficiency in sub-surface distribution is fostered by a slow continuous rate of application rather than by an intermittent application at a higher rate40 ,this agrees in every respect with the author's own experience1 and confirms his opinion that intermittent discharges to percolating filters should only be resorted to in cases where it is absolutely necessary in order to assist in securing uniformity of distribution1 or to ensure a sufficient volume for the operation of the appliances adopted for distribution4 ,among the former may be cited fixed spray nozzles and jets from fixed pipes1 in which cases an intermittent supply is useful in causing a regular variation of the head upon the orifices1 thus varying the distance to which the jets or sprays are thrown1 and producing greater uniformity of distribution per unit of area covered4 ,examples of cases1 where intermittent supply is necessary in order to discharge the volume required to operate the appliances adopted for distribution1 are found in connection with most types of fixed distributors and nearly all types of automatic revolving distributors4 ,in the case of the latter1 it is well known that a certain minimum head is necessary to overcome the friction due to the resistance of the air and to the weight of the apparatus itself on its bearings4 ,however small this friction may be1 it needs a volume of sewage slightly in excess of that required to fill the spray-holes1 which must be large enough to take the maximum flow of sewage when working under the maximum head4 ,it frequently occurs1 especially in small schemes1 and in schemes where the percolating filters are preceded by contact beds or slate beds1 that the rate of flow of the sewage is at times so low that it is not equal to the minimum volume required to operate the distributor1 and1 in the absence of any arrangement to overcome the difficulty1 the distributor would cease to revolve and the sewage would trickle through the spray-holes without proper distribution4 ,the same difficulty arises in connection with many of the fixed methods of distribution1 and it is most readily overcome by the use of a dosing tank fitted with an automatic syphon or valve1 by means of which the sewage is held-up in the tank until it reaches a certain predetermined level1 and is then discharged at a given rate to the filter4 ,when the tank is empty the discharge ceases1 and the sewage is again held-up as before4 ,in the case of large installations1 or schemes where the whole of the sewage is pumped and the rate of flow to the filters is thus under control1 it is not necessary to use a dosing tank for the purpose of providing the rate of discharge to the filters necessary to keep the distributor in motion4 ,it is1 however1 maintained in some quarters that intermittent supply is desirable in any case1 in order to secure alternate periods of work and rest for aeration4 ,there is one obvious disadvantage in this method of working4 ,assuming that during the maximum rate of flow of the sewage the volume which comes down in #e minutes is stored in a dosing tank1 and discharged to the filters in #b minutes1 it is clear that the rate of distribution is twice as great as it would be if the distribution were continuous over the whole period of #e minutes4 ,it is claimed that the disadvantage of the higher rate of distribution is counteracted by the #b minutes of rest and aeration1 but on this point there is room for doubt1 especially when the conditions which come into play during the average and minimum rates of flow of the sewage are taken into consideration4 ,taking the average rate as equal to one-half the maximum rate1 it will be seen that the dosing tank will discharge every #aj minutes1 but the time in which its contents are delivered to the filter will still be #b minutes1 so that under these circumstances the rate of distribution on the filter will be four times as much as it would be if the distribution were continuous4 ,during the minimum rate of flow of the sewage the conditions are still worse1 and it is difficult to accept the theory that periods of rest for #g minutes will compensate for excessive rates of distribution at four times the rate under continuous operation for periods of #b min4 at a time4 ,those who advocate intermittent supply under all circumstances would appear to have lost sight of the fact that very ample periods of rest are already provided by all revolving distributors4 ,when working at the rate of one revolution per minute1 the average time taken by each arm to pass over any one point on the surface of the filter may be taken as #je second4 ,before the succeeding arm reaches the same point a period of #ae seconds will have elapsed1 so that under these conditions the ratio of the periods of work to periods of rest is as #a to #cj4 ,in other words1 even during continuous distribution1 the time allowed for rest and aeration is thirty times as much as that during which the sewage is actually being delivered to the filter1 and there would thus appear to be no reason for unnecessarily adding to the periods of rest by means of dosing tanks1 especially as such a course involves a greatly increased rate of distribution at all times when the discharge actually takes place4 ,there is1 of course1 the possibility of adopting the happy medium1 which would consist of a dosing apparatus of such a type that it would provide a continuous supply during the maximum flow of the sewage1 and only act as an intermitting appliance during the minimum rate of flow4 ,this is probably the best arrangement to adopt in all cases where a dosing apparatus is absolutely essential4 ,as previously stated1 however1 there are many cases where the conditions render the use of a dosing tank absolutely necessary to prevent the stopping of the distributor1 and these have brought about the introduction of several types of automatic syphons and valves1 all arranged specially for the purpose of giving intermittent discharges to filters1 contact beds1 areas of lands1 and so forth4 ,there are various methods of constructing dosing tanks1 all dependent upon the arrangement of the preliminary processes and the filters which follow them4 ,in nearly all cases1 however1 it is found necessary to reduce the fall taken up by the dosing tank to the minimum1 and the different syphons and valves have thus been designed to work with the least possible head4 ,one point in the construction of dosing tanks should not be overlooked1 i4e4 the provision of a washout valve for use when it becomes necessary to clean out the tank4 ,it may be noticed here that neither the ,fiddian type of distributor1 on the water-wheel principle1 nor the power-driven distributors1 require any dosing tank to keep them in motion during the periods of minimum flow of the sewage4 ,in the case of the ,fiddian distributor the apparatus remains standing until the buckets are filled1 and each time these discharge their contents the distributor is moved forward a short distance4 ,under these conditions1 however1 the disadvantage of long intervals of rest between comparatively large discharges of sewage still remains4 ,undoubtedly the most even rate of distribution under all conditions is secured by the use of power-driven distributors1 whether of the rotary or travelling type1 but these can only be economically adapted for use in large installations or where power is available at a very low cost4 ,illustration3 ,,fig4 #aba;a4 ,t tank4 ,c carrier4 ,p supply pipe4 ,f filter4 ,e effluent channel4 ,h humus tank4 ,illustration3 ,,fig4 #aba;b4 ,t tank4 ,c carrier4 ,p main supply pipe4 ,p#a branch supply pipe4 ,v regulating valve4 ,w washout valve4 ,f filter4 ,e effluent channel4 ,h humus tank4 ,apart from the question of continuous versus intermittent methods of feeding percolating filters1 there still remains the problem of deciding whether the actual connections between the tanks and the filters shall be in the form of channels 7carriers7 or pipes4 ,for fixed sprays and revolving distributors1 which involve the use of pressure due to a column of liquid1 the actual connection to the apparatus must be in the form of a pipe extending at any rate to the outside of the filter4 ,whether it should be continued beyond this point in pipe form or in a channel depends entirely upon local conditions1 such as the slope of the ground1 the planning of the filters1 and the relative cost of the two methods4 ,there is one thing to be said in favour of pipes1 i4e4 that there is less chance of a nuisance being created by the evolution of foul gases from the sewage than in the case of open channels4 ,on the other hand1 channels may be1 and frequently are1 covered in4 ,whichever method is adopted1 care should be taken to provide a valve or penstock on the connection to each separate filter1 in order to be in a position not only to throw any filter out of work when desired1 but also to regulate the rate of supply to each filter independently of the others4 ,washout valves should also be provided on the channels or pipes1 in suitable positions4 ,where the filters are arranged in groups1 as suggested in ,figs4 #ge and #gg1 the intervening spaces may be used to accommodate a simple receiving tank1 or a dosing tank1 to which the sewage or tank effluent may be conveyed by an elevated channel or by a pipe under pressure4 ,the connections to the adjacent filters may then be provided in the form of pipes leading from this central tank direct to the distributor at the centre of each filter4 ,if the receiving tank or dosing tank in such cases is built upon piers1 the floor of the tank will come above the level of the surface of the filters1 and the space below may be utilised for an effluent receiving chamber or even for a settling tank to arrest the solids in suspension in the effluent4 ,there are many ways in which the supply to filters may be arranged1 and the preceding notes are merely intended as suggestions1 which may be elaborated as found desirable to suit conditions which vary almost in every case4 ,illustration3 ,,fig4 #aba;c4 ,t tank4 ,d dosing tank4 ,p supply pipe4 ,f filter4 ,e effluent channel4 ,h humus tank4 ,figs4 #aba;a and #aba;b have been prepared to show conditions under which channels and pipes respectively would be suitable for supplying the tank effluent to the filters4 ,fig4 #aba;c is the plan of a works where a dosing tank is used to deliver the tank effluent intermittently through separate supply pipes to each of the filters4 ,if the valves on the supply pipes are properly adjusted1 each filter will receive an equal proportion of each discharge from the dosing tank4 ,an alternative method is to provide an apparatus by means of which each separate discharge from the dosing tank is delivered in rotation to each of the filters4 ,in cases where the appearance of the works must be taken into consideration1 the method of arranging the tanks and filters suggested in ,fig4 #aba;d may be adopted4 ,by this means the space covered by the works is utilised to the utmost1 and the tanks are of the form by which uniformity of distribution and the maximum reduction of velocity is secured4 ,on the other hand1 it is probable that the slope of the site will only rarely suit this arrangement4 ,illustration3 ,,fig4 #aba;d4 ,o outfall sewer4 ,s screen chamber4 ,d detritus tank4 ,t settlement tank4 ,c carrier4 ,p supply pipe4 ,f filter4 ,e effluent channel4 ,h humus tank4 ,dosing ,apparatus4--,various methods of providing intermittent supply are in use4 ,among these one of the first was a simple form of balanced valve with float4 ,this1 however1 has been superseded by other types1 among which the syphons are the simplest form4 ,one of the first of this type specially designed for the purpose in question was the low-draught syphon1 manufactured by ,messrs4 ,adams ,hydraulics1 ,ltd41 and shown in ,fig4 #abb4 ,the special feature of this apparatus is that it can be arranged for a small depth of sewage in the dosing tank4 ,it will work with any depth from #f inches upwards4 ,these syphons can also be arranged to work singly1 in pairs1 each one coming into action alternately1 or in numbers of three and upwards1 when they can be adjusted to work in sequence or simultaneously4 ,illustration3 ,,fig4 #abb4--,,low-,,draught ,,dosing ,,syphon4 ,another type of syphonic dosing apparatus is that supplied by the ,patent ,automatic ,sewage ,distributors1 ,ltd41 and shown in ,fig4 #abc4 ,in this case a syphon is combined with a mechanical valve operated by floats1 hence the name 8auto-mechanical syphon40 ,a further type of syphonic dosing apparatus is manufactured by ,messrs4 ,george ,jennings1 ,ltd41 as shown in ,fig4 #abd4 ,these syphons are arranged to work in regular sequence1 and are operated by means of air valves1 which are shown mounted on a frame and connected by means of air pipes to the syphons4 ,the sequence is obtained by means of cams1 fixed in different positions on a shaft1 which is rotated by means of a float actuated by the rise and fall of the liquid in the dosing tank4 ,illustration3 ,,fig4 #abc4--;,,dosing ,,syphon4 ,a different type of dosing apparatus is the 8,coleman0 valve1 manufactured by ,the ,ames ,crosta ,sanitary ,engineering ,company1 ,fig4 #abe4 ,this consists of a balanced valve1 suspended from a hollow lever which contains mercury1 and has a branch provided with a float actuated by the rise and fall of the liquid in the tank4 ,as the sewage rises in the tank1 the float overcomes the resistance of the balance weight on the lever1 which is lifted1 and the mercury falls to the lower end of the lever4 ,the combined action of the float and the mercury opens the valve1 and the sewage is discharged4 ,when the tank is emptied1 the apparatus resumes its former position ready for the next dose4 ,illustration3 ,,fig4 #abd4--;,,dosing ,,syphons4 ,another type of dosing apparatus is manufactured by ,messrs4 ,mather and ,platt1 ,ltd4 ,this consists primarily of a flap valve1 counterbalanced weights1 and a balance vessel or drum1 which is filled gradually with liquid1 the whole being pivoted about a horizontal axle4 ,when the measuring chamber and balance drum are both empty1 the counterbalance weights raise the latter and allow the flap valve to close1 the balance drum then being in its highest position4 ,as the measuring chamber fills1 a portion of the sewage is allowed to pass from it into the balance drum1 which is thus gradually filled1 and at a given level its weight will suffice to overcome the counterbalance weights and the pressure of the sewage on the flap valve1 and will open the latter1 thus allowing a measured quantity of sewage to be discharged into the troughs or pipes for spreading over the filter4 ,the balance drum discharges its contents meanwhile1 and thus1 when the measuring chamber is empty1 the flap valve closes again by the action of the counterweights1 and the chamber is ready to receive another quantity of sewage 7,fig4 #abf74 ,illustration3 ,,fig4 #abe4--8;,,coleman0 ,,dosing ,,valve4 ,messrs4 ,george ,kent1 ,ltd41 have introduced several different types of dosing apparatus1 which can be arranged to draw off less than #f inches head of water and any greater depth4 ,in one case the apparatus1 ,fig4 #abg1 consists essentially of a seating ,s1 through which the liquid discharges1 a valve-cap ,c1 attached to arms which rotate about the pin ,p and nearly balanced by the weights ,w1 also by floats ,f ,f attached to a frame1 also rotating about ,p and carrying two adjusting weights ,a ,a4 ,the apparatus is actuated by the rise of the liquid1 raising the floats and lifting the cap ,c1 which returns to its position after the discharge has taken place4 ,for greater depths a different type is used1 as shown in ,fig4 #abh4 ,in this case the apparatus consists of a valve seating ,s1 through which the liquid discharges1 two floats ,a and ,b1 a controlled device for giving a sudden release and for regulating the levels at which the valve is opened or closed1 and an alternating gear ,g1 which is fitted with two or more valves placed in the chamber and operated in rotation4 ,the action of the apparatus is as follows3 ,when the liquid in the dosing chamber reaches the top level1 the float ,a has acquired sufficient buoyancy to cause the shoulders of the plate ,k to suddenly push aside the rollers at the ends of the weighted levers ,l ,l of the control device4 ,the lugs ,t ,t then come in contact with the collar ,r1 and the valve-cap ,c and the float ,b are lifted4 ,the tank discharges until the floats ,a and ,b have lost sufficient buoyancy to cause the bottom shoulders of the plate to push aside the rollers and allow the valve to close4 ,illustration3 ,,fig4 #abf4--;,,dosing ,,valve4 ,illustration3 ,,fig4 #abg4--;,,dosing ,,valve4 ,this apparatus is applied in various ways for different purposes in connection with sewage works1 and the same firm also manufacture special valves for giving a measured discharge under various heads4 ,illustration3 ,,fig4 #abh4--;,,dosing ,,valve4 ,illustration3 ,,fig4 #abi4--;,,distributing ,,and ,,dosing ,,apparatus4 ,the ,ames ,crosta ,sanitary ,engineering ,company1 ,ltd41 also supply a very ingenious method of providing intermittent supply to filters1 as shown in ,fig4 #abi1 which is equally suitable for percolating filters1 for contact beds1 or for intermittent filtration on land4 ,this machine is arranged to give any desired timed discharge to the beds in rotation1 or to discharge measured volumes to the beds in rotation4 ,by means of valves or weirs1 the machine is arranged so that additional beds in the series are automatically brought into operation as the increase in flow demands1 and the additional beds brought into action go out of action as the flow decreases4 ,the illustration shows a machine for delivering timed volumes on a series of six beds4 ,the square chamber is divided into six divisions by means of iron plates2 each division is connected to one of the six beds by means of a pipe4 ,a circular dish or vessel is suspended over these divisions1 and revolves on ball-bearings carried on the bridge4 ,the circular dish is provided with a weir at its circumference1 and the sewage or tank effluent which enters the dish from the pipe in the centre is diverted by means of the weir or outlet to one of the divisions supplying the beds4 ,the upright shaft from which the revolving dish is suspended is fitted with a six-toothed ratchet wheel1 and1 by the rise and fall of a float in the liquid of the actuating tank1 a pawl is moved along until it engages with the next tooth of the ratchet wheel4 ,when the pawl has caught the tooth of the ratchet wheel the outlet valve in the actuating tank is opened1 and as the liquid flows out of the tank the float descends1 and by means of levers the pawl is moved one-sixth of a revolution2 the pawl being engaged with the ratchet wheel1 the dish is revolved one-sixth of a revolution1 and the weir is thus brought over the next division1 and consequently the next bed receives the flow4 ,extra weirs can be arranged at various levels1 so that if more sewage is coming than that required for one bed1 a portion of the liquid would flow over one or more of the weirs1 and so on1 to the respective beds4 ,the flow to the actuating tank is taken from the feed channel1 and can be set to fill the actuating tank in any desired period of time4 ,the discharge from the actuating tank can be conveyed either to a special plot of land1 or into the revolving dish4 ,an ingenious device is arranged so that any bed in the series can be instantly shut out of action should it become overworked4 ,in an apparatus for feeding revolving sprinklers1 arrangements are made for bringing the extra beds into operation by means of valves controlled by the flow of sewage4 ,illustration3 ,,fig4 #acj4--;,,balance-,,valve ,,dosing ,,apparatus4 ,messrs4 ,glenfield and ,kennedy also manufacture a balance-valve type of dosing apparatus operated by means of floats and buckets4 ,this is shown in ,fig4 #acj4 ,illustration3 ,,fig4 #aca4--;,,distributing ,,and ,,measuring ,,apparatus4 ,the 8,uniform0 automatic distributor1 manufactured by ,messrs4 ,whitehead and ,poole1 is designed for the automatic distribution of measured volumes of liquid to filters or other areas in regular rotation4 ,this is shown in ,fig4 #aca1 and the principles on which it is constructed involve rotating arms carried on a float operated in a closed central chamber4 ,the arms are rotated by the reaction of the discharge of the liquid1 but are locked so as to remain stationary in one position1 continuing to feed one filter until the head of liquid actuating a regulating cock and tipper releases the locking device and permits the rotation of the arms to the next bed1 where the process is repeated1 and so on to all the filters in rotation4 ,the 8,ponding or ,intermitting ,valve10 supplied by the ,septic ,tank ,co41 is shown in ,fig4 #acb4 ,the essential features of this apparatus are two cylindrical vessels of cast-iron or other suitable material1 approximately of the same shape1 weight and displacement4 ,one vessel is used as a bucket and the other as a bell4 ,they are suspended from two equal arms of a pivoted lever at approximately the same distance from the standard carrying the lever4 ,on the same end of the lever to which the bell is hung1 an ordinary lift-up valve is attached1 the seat of which is at or below the low-water level in the ponding chamber4 ,this valve is connected with the lever by means of a linked rod1 chain1 or other suitable arrangement4 ,the cubical content of the bell and bucket is sufficient to ensure the displacement of the liquid1 in excess of that required to lift the valve from its seat1 by rocking the lever to which it is attached4 ,in the bottom of the bucket a draw-off valve is provided for the purpose of emptying same4 ,this valve is constructed so as to prevent the liquid passing through it into the bucket as it rises in the chamber1 and to open and allow the contents of the bucket to escape when the water in the ponding chamber has almost been discharged4 ,the operation of the apparatus is as follows4 ,the ponding valve being closed1 and the supply of liquid being turned into the ponding chamber1 the liquid will rise4 ,on reaching the small ball in the bottom of the valve of the bucket1 the ball will float and close this bucket valve1 so as to prevent the entrance of the liquid through and into the bucket4 ,the liquid continuing to rise1 will gradually and simultaneously submerge the bell and the bucket4 ,the upper edge of the bucket is fixed at the predetermined height to which the liquid is to rise in the ponding chamber4 ,the bell and bucket being of the same size and weight1 and being hung so that the one is level with the other1 the displacement of both will be equal up to the time the liquid reaches the upper edge of the bucket1 and consequently no movement of the lever will take place4 ,on the liquid rising above the top edge of and filling the bucket1 it will cause the displacement of the bucket to be reduced to much less than the displacement of the bell1 and this difference is sufficient to lift the valve from its seat1 and discharge the contents of the ponding chamber4 ,as the liquid in the chamber recedes1 the bucket and the bell will both be gradually left suspended in the air4 ,until the liquid in the chamber drops below the bottom of the bucket1 the latter will remain full2 on the water continuing to fall1 the ball in the small valve at the bottom of the bucket will drop1 allowing the contents of the bucket to escape4 ,on the bucket being emptied of its contents1 the weight of the bell1 together with the valve and chain or rod1 will overcome that of the bucket1 the valve will close1 and the liquid commence to pond in the chamber again4 ,illustration3 ,,fig4 #acb4--,,the ,,septic ,,tank ,,co4',s ,,ponding ,,valve4 ,illustration3 ,,fig4 #acc4--;,,auto-,,mechanical ,,dosing ,,syphon4 ,the special syphons manufactured by ,messrs4 ,burn ,bros41 described under contact bed apparatus1 are also suitable for use as dosing syphons1 and work singly or in sequence1 and give intermittent discharge to filters or to land 7see ,fig4 #ade1 page #bah74 ,an auto-mechanical type of syphon for dosing tanks is supplied by the ,carlton ,engineering ,co41 and is illustrated in ,fig4 #acc4 ,,effluent ,,settling ,,tanks ,,or ,,humus ,,pits4 ,reference has already been made1 under the heading 8,grading of ,filtering ,material10 to the advisability of using coarse material1 for the reason that the converted organic matter will in that case readily pass away in the effluent1 and thus prevent the choking of the filter4 ,even with finer material1 a certain amount of solids in suspension will be found in the effluent1 and1 in order to produce a final effluent suitable for discharge into any stream or watercourse1 it is necessary to arrest and remove these suspended solids4 ,this fact has been recognised by the ,royal ,commission on ,sewage ,disposal1 who recommend the adoption of effluent settling tanks with a capacity equal to two hours' flow of the sewage1 and provided with means for removing the deposit4 ,the solids in effluents from percolating filters are rather difficult to arrest1 as they are in the form of very finely divided matters in suspension4 ,many methods have been tried in various places1 but in the author's experience he has found that the chief factor in securing a satisfactory settlement of these solids1 is the reduction to the minimum of the velocity of the effluent in its passage through the settling tank4 ,if this principle is adopted1 the simplest form of tank is similar in construction to that suggested for detritus tanks1 so long as the outlet end is constructed in the form of a weir of the greatest possible length under the circumstances4 ,such a tank is illustrated in ,fig4 #acd4 ,by this means the rate of flow over the weir may be reduced to the minimum2 and if1 in addition to this1 the outlet at the bottom of the tank is arranged in the form of a plug valve fixed in a pocket below the lowest point of the floor proper1 near to the inlet end1 and the floor is laid with a sharp slope towards this outlet1 it will be found possible1 as a rule1 to draw off the deposit without discharging the entire contents of the tank1 as long as it is done at frequent intervals4 ,as there is a tendency for a scum to form on the surface of the liquid in these tanks1 it is desirable to provide a scum-plate of wood1 slate1 or other material1 as shown in the illustration1 and in all cases1 except the smallest schemes1 these tanks should be constructed in duplicate4 ,it may be mentioned here that the hydrolytic tank1 ,fig4 #cd1 page #eb1 and the separator of the ,septic ,tank ,co41 ,ltd41 ,fig4 #dg1 page #fe1 have both been adopted for use as effluent settling tanks4 ,illustration3 ,,fig4 #acd4--;,,effluent ,,settling ,,tank4 ,the deposit from effluent settling tanks1 as a rule1 rapidly dries without creating a nuisance when it is spread out in a thin layer upon a suitable draining bed similar to that suggested for dealing with sludge from settling tanks 7,fig4 #eh1 page #hc74 ,under favourable conditions as to fall1 the draining bed can be constructed below the level of the sludge outlet from the effluent settling tank1 and the deposit can then be drawn off by gravitation4 ,there is1 however1 still the problem of disposing of the liquid flowing from the bed1 and as this should have a free outlet1 it usually happens that the levels do not permit of the discharge of the deposit by gravitation4 ,under these circumstances the outlet should still be arranged as shown1 ,fig4 #eh1 but it should be connected to a sludge well fitted with a chain-pump1 or other means of raising the deposit to the draining bed1 which may thus possibly be situated at the same level as the similar beds for the sludge from the settling tanks4 ,when dry1 this deposit may be spread out on the land1 or used in gardens and on farms as a manure4 ,,sand ,,filters4 ,it would probably be more correct to use the term 8fine-grain filters0 to describe the alternative methods occasionally adopted to deal with the effluents from percolating filters1 as they do not always consist of sand4 ,fine clinker1 ashes1 broken saggars1 and similar material1 is equally suitable so long as it is of a gritty nature and not wholly dust4 ,the term 8sand-filters0 is1 however1 used here1 as it is well known in connection with the filtration of drinking water1 and the method of construction is practically the same4 ,although primarily designed for the purpose of arresting the suspended solids in final effluents1 and thus required to act simply as mechanical strainers1 sand filters have the additional advantage of increasing the degree of purification1 especially from a bacterial point of view4 ,the most important factor to be considered in constructing these filters is the grading of the material4 ,it must not be too fine or contain too great a proportion of dust1 or it will rapidly become clogged and involve much labour and expense in cleaning the surface layer4 ,the nearest approach to perfection in material for this purpose is the coarse ,leighton ,buzzard filter sand4 ,as in the case of the best material for the percolating filters themselves1 it may cost a little more than other less satisfactory kinds1 but it will generally be found to be the cheapest in the end4 ,in constructing filters of this type1 whether composed of sand or other material1 it is essential that the bottom layer should be of a coarser grade1 in order to provide free drainage4 ,in a general way it will be found satisfactory to have a series of #b-;inch agricultural drain pipes laid on the floor and converging towards the outlet4 ,over the whole floor should then be laid a layer #f inches deep of gravel1 broken bricks or stones of the size of walnuts1 upon this a layer #c inches deep of pea gravel1 and at the top a layer not less than #i inches deep of suitable sand or other fine grade material4 ,the surface of the filter should be well below the level of the inlet1 in order to allow the liquid to pond up on the surface #f inches to #i inches in depth without backing up to the level of the floor of the percolating filter4 ,one of the difficulties encountered in operating filters of this type is to secure even distribution over the whole area4 ,the means to be adopted for this purpose should be simple and easily cleaned1 and it is usual to find troughs of wood or iron1 glazed ware channel-pipes and similar arrangements in use4 ,unfortunately these do not effectively cover the whole area until the sand has been saturated and the surface slightly coated1 thus preventing the liquid from passing through as fast as it comes in4 ,when this occurs1 however1 the time for cleaning the surface is not far distant1 and when the filter is brought into use again the whole preliminary process has to be repeated4 ,the best way of avoiding these difficulties would appear to be to arrange the filter in such a way that the liquid must cover the whole area from the very beginning4 ,this can be accomplished by fixing the normal outlet above the level of the surface of the filter as suggested1 ,fig4 #ace1 where the final effluent discharge is normally from the end of the swivel-jointed pipe when in its vertical position4 ,when it becomes necessary to clean the filter and drain it for purposes of aeration1 the swivel-jointed pipe is simply lowered to the floor of the outlet-chamber1 as shown in plan1 and raised again when the filter is brought into operation4 ,illustration3 ,,fig4 #ace4--,,sand ,,filter4 ,filters of this type should never be less than two in number1 so that one may be in work while the other is being cleaned4 ,it would probably be advisable to have even three or four filters for schemes of moderate size1 so as to provide longer or more frequent intervals of rest for aeration4 ,it will be obvious from the preceding observations that these filters must be substantially constructed and made absolutely watertight4 ,when dealing with a good effluent from percolating filters or contact beds1 these final sand filters may be provided at the rate of #a square yard for every #ejj gallons of the daily dry weather flow4 ,where ample fall is available1 careful consideration should be given to the advisability of operating these sand filters in the same manner as percolating filters1 i4e4 by using revolving sprinklers for the purpose of distribution without submerging the filtering material4 ,this applies particularly in cases where it is desirable to secure a very high degree of bacterial purification4 ,recent investigations have shown that sand filters for drinking-water1 when operated in this manner1 are highly efficient and involve less expense for maintenance4 ,in addition to this they require less cleaning1 so that a much smaller area is thrown out of work during cleaning operations1 and a smaller total area of filter surface is needed than in the case of similar filters operated on the submerged system4 ,the additional fall required for the revolving sprinklers will usually be a serious difficulty in the case of sewage disposal works1 but where it is available1 and the extra cost entailed is not of great importance1 the idea deserves consideration4 ,filters of this type should be preceded by an effluent settling tank as previously described4 ,,contact ,,beds4 ,the almost universal adoption at the present time of biological methods of sewage purification by means of artificial filters1 is due entirely to the original experimental work of ,mr4 ,w4 ,j4 ,dibdin1 at the ,barking ,outfall ,works of the ,london ,county ,council4 ,these experiments were carried out with a contact bed1 and during the subsequent ten years an enormous number of works were constructed upon this principle4 ,at the present time1 however1 it is a somewhat rare occurrence to find contact beds proposed for sewage disposal schemes of any size4 ,it has been stated that the principle upon which they are operated is unscientific1 that they rapidly become clogged and useless1 and that1 in any case1 they are not capable of dealing with sewage at the same rate as percolating filters1 or of producing such a high degree of purification4 ,with regard to the first point it would be futile to endeavour to explain what is and what is not scientific4 ,this must be left to the scientists4 ,that contact beds have in many cases become clogged and useless cannot be denied1 but there is also very little doubt that this unsatisfactory result has been due to one or more of the following causes3 7a7 overwork1 7b7 improper methods of operation1 7c7 the use of unsuitable material for filling the beds1 7d7 insufficient sub-drainage4 ,it was most unfortunate that for some years the general idea of a contact bed was that it consisted of a simple excavation in the ground1 filled with coke or similar material1 into which the sewage was discharged1 held up for two hours1 and then drawn off2 a very simple but crude affair altogether4 ,it is now known that contact beds1 like other systems1 can only deal with limited volumes of sewage1 the actual amount depending upon the character of the sewage and other factors2 that there is a proper method of operating the beds1 and that it must be strictly adhered to if the best results are to be produced2 that unsatisfactory material is worse than useless1 and that very ample means of sub-drainage are absolutely essential to the continued efficiency of the beds4 ,it is probable that if these essential factors had been properly understood and acted upon from the outset1 there would have been very few failures to record4 ,it has been stated that contact beds are obsolete1 but there are engineers who even now recommend this system1 and consider it satisfactory under some1 if not under all conditions4 ,in the opinion of the author contact beds are not obsolete1 and there are cases where the conditions preclude the adoption of any other method of purification4 ,under these circumstances1 it is considered desirable to describe in the following pages the details of design and construction which have been found by experience to be necessary to ensure satisfactory results4 ,general ,principles of ,design4--,the first point to be decided before commencing the design of a scheme of contact beds is whether single1 double1 or triple contact is necessary to produce the desired degree of purification1 and this will depend upon the strength of the sewage and the destination of the final effluent4 ,single contact alone will not be sufficient1 except in a very few cases where the sewage is weak 7highly diluted71 and even then it will necessitate the use of fine-grade material for filling the beds1 and consequently a tank effluent of exceptional quality as regards the matters in suspension in order that the fine material may not be rapidly choked4 ,where a sufficient area of land of a suitable character can be procured at a convenient level for treating the effluent from the beds1 single contact may be adopted with material of medium-grade1 but even in this case special attention must be devoted to the preliminary process in tanks1 so as to reduce the amount of solids in suspension in the tank effluent to the minimum4 ,as a rule it will be found safer to adopt double contact1 as the primary beds may then be filled with coarse grade material1 which will be less liable to choke1 and it will not be necessary to rely so much upon the land or any other final process that may have been provided4 ,in special cases1 and particularly where the sewage is strong1 or an exceptionally high degree of purification is essential1 triple contact should be adopted1 but the tertiary beds may consist of a set of sand filters similar in construction to those described on pages #ahe to #ahh4 ,in some quarters the question of the grading of the material is considered of slight importance1 and very little difference has been made in the size of the material for the primary and secondary beds1 but in the author's opinion it is absolutely essential that each series of beds should be filled with finer material than the preceding series1 and the material in the final stage of treatment should be as fine as possible1 so long as it does not contain any dust4 ,in making these statements1 it is assumed that the question of sub-drainage will be dealt with on the lines recommended later under that heading4 ,another factor which has an important bearing upon the general design of a scheme of contact beds1 is the method of operation which is to be adopted4 ,it is generally assumed that all contact beds are worked in what is known as eight-hour cycles3 viz4 #a hour filling1 #b hours standing full1 #a hour emptying1 and #d hours standing empty for rest and aeration4 ,there has1 however1 been a tendency in the past to overlook the fact that the periods of standing full1 and of emptying the beds1 are the only sections of the cycle which are1 as a rule1 under absolute control4 ,unless special provision is made for the purpose1 the time taken to fill each bed depends entirely upon the rate of flow of the sewage to the works1 and the period of rest empty also depends upon the frequency with which the beds are filled1 and thus indirectly upon the rate of flow of the sewage4 ,for example1 a set of four beds designed to receive each three fillings per day in wet weather1 should not receive more than one filling per day in dry weather4 ,assuming that one-half the total flow comes down in six hours1 it will be found that it takes six hours to fill two beds in the middle of the day1 or three hours to fill one bed4 ,during the remaining eighteen hours the other two beds are filled1 one of them in say six hours and the other in twelve hours4 ,the times taken to fill the four beds in this scheme would therefore be--,no4 #a1 three hours2 ,no4 #b1 three hours2 ,no4 #c1 six hours2 and ,no4 #d1 #ab hours4 ,in each case the period of filling is thus much in excess of the one hour prescribed under the eight hours cycle4 ,the obvious remedy is to subdivide the total area into a larger number of smaller beds1 but if this is carried to its logical conclusion it will be seen that there must be #bd beds if the time taken to fill any one bed is not to exceed one hour4 ,while it is very desirable to arrange this subdivision in order to secure the proper cycle of operations1 the number of schemes where it is economically practicable are few1 and recourse must be had to some other method of reaching the same end4 ,this has already been recognised by most engineers1 and provision is now usually made for a tank known under various names1 such as dosing tank1 collecting tank1 equalising tank or holding-up tank1 in which the tank effluent is stored until the volume accumulated is equal to the capacity of one contact bed1 and the latter is then filled within the regulation time of one hour4 ,if the necessity for making provision on these lines to ensure the proper working cycle had been recognised in the early days of contact beds1 it would doubtless have prevented the troubles which have arisen in many places4 ,from the preceding observations1 it will be seen that it is very necessary to come to a decision as to the method of operation to be adopted1 before designing any scheme of contact beds4 ,if the method of subdivision into a large number of small beds is preferred1 the planning of the separate series1 and the probable cost of the additional work involved1 must be taken into consideration4 ,on the other hand1 if a smaller number of larger beds with a suitable dosing tank are preferred1 the extra fall required for the latter must be provided for1 even if it involves the reduction of the depth which would otherwise be available for the beds themselves4 ,illustration3 ,,fig4 #acf4 ,there is still another matter which has a considerable influence upon the general design of a scheme of contact beds1 viz4 the slope of the ground upon which they are to be constructed4 ,if it has a fairly rapid and even slope1 the tanks and beds may be arranged close together1 as shown in ,fig4 #acf4 ,the only part that needs special care in this case is the cross-wall between the primary and secondary beds1 which will need strengthening1 especially in its lower half1 in order to resist the extra pressure it is required to take4 ,illustration3 ,,fig4 #acg4 ,where the slope is not so great1 a saving in the cost of excavation may be effected by arranging the separate tiers of beds at some distance apart1 as indicated in ,fig4 #acg1 and connecting one with the other by pipes4 ,the aim to be attained in arranging the beds under these conditions is to have the entire area of the floors on solid soil1 with the walls half in and half out of the ground4 ,another set of conditions occasionally met with1 is where the site of the works is perfectly flat and the position of the outlet for the final effluent involves the construction of the secondary beds either wholly or partly below the surface4 ,in such cases the primary beds will come above ground1 and it will then be found economical to arrange each set of beds in two rows end to end1 with a central combined supply channel and effluent carrier1 the latter being formed in the space between the walls which support the former1 as shown1 ,fig4 #ach4 ,if there is not sufficient head to allow of the supply channel being made deep enough to serve as the dosing tank1 the latter may be constructed across the ends of the settling tanks1 as suggested in ,fig4 #aci1 or in any other convenient position4 ,a dosing tank in this position lends itself to the method of feeding the beds by means of closed pipes instead of by open channels1 whether in sets of four1 with a central chamber for the inlets and outlets illustrated in ,fig4 #aci1 or in series as ,figs4 #acf and #acg4 ,illustration3 ,,fig4 #ach4 ,there are doubtless other alternatives1 or combinations of methods1 which may be adapted to meet the exigencies of peculiar conditions of site and fall1 but the foregoing details will probably suffice to suggest ideas to those in need of them in designing schemes of contact beds4 ,general ,construction4--,the most important point to be borne in mind in constructing contact beds is1 that they must be absolutely watertight4 ,should they leak in any way1 the sewage may pass away untreated2 or it may find its way into adjacent beds1 and thus prevent these from being properly aerated during the periods of rest when empty4 ,it is therefore evident that they should be constructed in a substantial manner4 ,the floors are usually of concrete1 and the thickness of the floor will depend upon the nature of the subsoil4 ,if for any reason the floors have to be laid upon made-up ground1 provision should be made by means of piers or cross-walls1 carried down to the solid subsoil to support the floor1 independent of the made-up ground which is1 in all cases1 absolutely untrustworthy4 ,the walls of the beds may be constructed either of concrete throughout or of brickwork in cement1 and they should be of such a thickness that they will withstand the pressure of the head of water which would result if the beds were filled to the top of the walls4 ,it will not be found satisfactory to place reliance either upon brickwork or upon concrete alone to form a watertight bed1 and in both cases the whole of the floors1 as well as the walls1 should be rendered with cement mortar in the proportion of #b parts of sharp clean sand to #a part of ,portland cement4 ,no rendering should be done during frosty weather or during excessive heat1 as in both cases it will usually be found defective1 and it is better to stop the work altogether for a time than have to patch it up afterwards4 ,illustration3 ,,fig4 #aci4 ,one safeguard which can be adopted to prevent difficulties later on1 is to insist upon testing all such beds with water to the full height before any of the filtering material is placed in position4 ,any slight defects which may appear can be made good then at very little expense4 ,if the defects are not discovered until after the beds are filled with the filtering material1 they can only be properly rectified by removing the material1 and this involves a considerable outlay4 ,in order that these tests may be carried out without friction1 it is necessary to stipulate clearly in the specification for the work that each bed is to be tested with water to the full depth before any material is placed in the bed1 and that the contractor must take full responsibility for making the beds absolutely watertight4 ,it is1 of course1 understood that the method of construction adopted by the engineer is such that1 if properly executed1 the beds will be absolutely watertight2 and1 in order to prevent any misunderstanding1 an item should be included in the quantities for the contractor to provide whatever sum he may consider necessary to allow for making these tests4 ,it may be thought sufficient to state simply that the contractor should make all absolutely watertight1 and to leave it to him to provide the means for doing so4 ,it will1 however1 be found more satisfactory to all concerned to provide all means both in specification and in the quantities for attaining the desired results4 ,it is not sufficient even to use the word 8watertight0 alone in this connection1 as the interpretation of this word may be subject to differences of opinion which are obviated by the addition of the word 8absolutely40 ,the foregoing observations refer not only to contact beds but to the tanks and other portions of the work which are required to hold water4 ,methods of ,distribution4--,much diversity of opinion exists with reference to the question of distribution in filling contact beds4 ,the many methods which have been tried in various places1 may be arranged under four headings1 viz4 7a7 above the surface of the material2 7b7 at the surface level2 7c7 just below the surface2 7d7 at the bottom of the bed4 ,some engineers hold the opinion that distribution over a large area of the material has no value1 and that it matters little how the bed is filled so long as the liquid finds its way into the interstices of the material with as little disturbance as possible4 ,the simplest method which fulfils these requirements is to allow the sewage to flow over the surface at the inlet end of the bed1 but this soon causes the surface at this point to become clogged1 and unless it is cleaned at frequent intervals the solids very quickly become washed down into the bed1 and in the end this portion of the material will have to be removed and washed before it can be used again4 ,the efforts to avoid this trouble have resulted in the numerous methods of distribution referred1 to above4 ,taking them in the order given1 the idea of discharging the sewage above the surface level 7a7 by means of elevated troughs or pipes1 has been to imitate to some extent the method found necessary in the case of percolating filters1 and thus aerate the sewage before it enters the bed4 ,the difficulties which arise in this case are that some extra fall is needed1 and the provision of the troughs or pipes with suitable supports is costly4 ,it is also extremely difficult to arrange the distribution by these means so that it shall be uniform over the whole area1 and unless this is done it cannot be of much advantage4 ,distribution at the surface level 7b7 may be provided by means of shallow grips in the material itself1 and these have the great advantage that if they become clogged to such an extent as to prevent the sewage from freely passing into the bed1 it is a small matter for the manager to cut a fresh grip in another direction and leave the first one to dry up when the sludge in it can be easily removed by hand4 ,another method is to use rows of stoneware channels1 or wooden or iron troughs1 with their edges set level with the surface of the material1 so that the sewage may flow over the edges or through holes or notches in the sides4 ,this is usually satisfactory1 but it is not an easy matter to maintain all the channels at the same level1 and after they have been in operation for a time it will be found that the material immediately under the troughs or channels is badly clogged1 and can only be cleaned or renewed by removing the channels4 ,sub-surface distribution 7c7 is arranged by means of perforated or open-jointed pipes1 laid below the surface of the material and thus out of sight4 ,the reasons for adopting this method are3 that it avoids the unsightliness caused by surface distribution2 that the surface is kept free from obstructions1 and thus allows free aeration when the bed is emptied2 and last1 but not least1 it prevents any nuisance arising from the evolution of obnoxious gases in the tank effluent whenever it is over-septicised1 a not infrequent occurrence in the case of old-fashioned schemes1 or in new works where the volume of sewage for which the tanks were designed has not yet reached its maximum4 ,this method has the disadvantage that when the openings in and between the pipes become choked1 more labour is involved in cleaning them than in the case of open channels or troughs on the surface4 ,filling from the bottom 7d7 is assumed to possess all the advantages and none of the disadvantages caused by the other methods4 ,the distribution is certainly uniform1 as the liquid first fills the sub-drains and then rises at the same level throughout the whole of the material1 forcing out any carbonic acid gas that may have accumulated in the lower part of the bed4 ,as the sewage does not appear on the surface at all1 there is no unsightliness and no trouble from bad odours4 ,on the other hand1 it is evident that the solids in suspension in the sewage or tank effluent are retained at the bottom of the bed1 especially in the under-drains1 and thus they will appear in large quantities in the effluent4 ,unless some special provision is made1 by means of an effluent settling tank or sand-filter1 to arrest these solids in suspension in the final effluent1 they will be liable to cause trouble in the stream1 and will1 in any case1 seriously affect the results of any analyses that may be made4 ,the usual manner of arranging this method of filling1 is to cause the sewage to flow into an open or covered chamber at the inlet to the bed1 the walls of the chamber being provided at the floor level with openings connected to the sub-drains laid on the floor of the bed4 ,whatever method of distribution is adopted1 it is desirable that the surface of the filter material shall be not less than #c inches above the highest level to which the sewage will rise1 so that the liquid may not be visible at the surface4 ,sub-,drainage4--,reference has already been made to the fact that lack of ample under-drains has often been the cause of the failure of contact beds in the past4 ,the general practice for a long time consisted in placing a layer of coarse material on the floor of the bed1 and providing a few rows of ordinary agricultural drain-pipes laid with open joints4 ,in some few cases special perforated pipes were used1 in others the pipes were partly embedded in the concrete floor4 ,in the opinion of the author1 however1 no drains in the form of pipes are satisfactory1 as they do not leave a space at the floor level as a free exit for the solids in the effluent4 ,where pipes are used it will generally be found after a few months' operation that these solids1 in the form of black sludge1 have accumulated along the sides of the pipes and among the material at the floor level1 and when this once commences the accumulation continues to take place1 rising gradually in the bed until the interstices are choked to such an extent that the liquid capacity of the bed is reduced to a fraction only of its original volume4 ,the trouble was intensified by the comparatively small number of the pipe drains usually found in the beds4 ,it was evidently assumed that the matters would travel laterally through the layer of coarse material at the floor level4 ,unfortunately an additional impediment to the free flow of these matters was caused in many cases by the want of sufficient fall on the floor itself4 ,very little consideration will show that a large area of floor requires a considerable slope in order to produce the velocity of discharge necessary to remove matters in suspension1 yet it was seldom that a gradient of more than #a in #bjj was provided1 and in a few cases the surface of the floor was absolutely flat4 ,under these conditions it is difficult to see how any other result could be expected4 ,it may be argued that it was not properly understood in those days that the solids in suspension 7converted organic matters1 the products of oxidation7 must be removed if the filtering material is to retain its working capacity1 but this fact has long been recognised in connection with percolating filters1 which have in most cases been constructed upon complete false floors1 provided with perforations1 and with a suitable slope on the surface of the actual floor4 ,there is very little doubt that the question of providing ample means of sub-drainage deserves special consideration2 and1 in the author's opinion1 the floors of all contact beds should be laid with much greater fall to the outlet than in the past1 and they should1 in addition1 be covered entirely with a false floor of special floor-tiles of the kind described in connection with percolating filters 7pages #ia to #id74 ,if the usual bottom layer of coarse material is then laid upon the false floor1 it will be found that the beds will maintain their normal working capacity for a much greater length of time than in beds constructed on the old style4 ,instead of arranging the slope on the floor from the inlet end to the outlet end of the bed1 it is preferable to construct an effluent channel with a suitable fall down the centre of the bed to the outlet1 and arrange the floor with a cross-fall from the sides to the centre channel1 which may be covered by slabs of concrete or stone laid upon the top of the floor tiles where they abut upon the edges of the channel as suggested1 ,fig4 #aci;a4 ,illustration3 ,,fig4 #aci;a4 ,material for ,filling ,contact ,beds4--,the remarks made under the heading 8,filtering ,material0 for percolating filters 7pages #aja to #ajc71 apply with equal force to contact beds4 ,in none of the many cases which have come under the observation of the author has it been possible to obtain such satisfactory results from other material as from clinker1 when used under the same conditions as to the strength and volume of the sewage treated4 ,it is true that excellent effluents have been produced by beds filled with burnt clay1 broken bricks or stones1 but it will usually be found that in such cases the material is more or less clogged1 and that the volume successfully treated per day is considerably less than that which would be dealt with by clinker4 ,the reasons are the same as those already mentioned in pages #aja to #ajc1 and there is no need to say more here than to recommend as strongly as possible the use of hard-burnt vitrified furnace clinker as already described for percolating filters4 ,the foregoing remarks apply more particularly to the material for coarse and medium-grain contact beds4 ,clinker of the kind described is equally suitable for fine-grain contact beds1 but it is difficult to break it to the required grade except at great cost1 and a considerable loss in bulk due to the production of fine dust4 ,for fine-grain beds1 requiring material specified to pass a -inch square mesh1 and to be retained on a -inch square mesh1 clean coke-breeze from gas-works 7not ashes7 will be found to be the most efficient4 ,the important point to be observed in preparing material for fine-grain contact beds is that1 while none of the particles should exceed inch in diameter1 as many as possible of the finer particles1 inch and #c_/af inch in diameter1 should be retained1 but all dust should be removed even if it necessitates washing the material for that purpose4 ,even the finer particles down to #a_/af inch diameter might be used1 but it will be found extremely difficult to arrange the sifting process to arrest these without retaining the dust as well1 especially if the material is at all damp1 as the fine meshes required for the purpose quickly become clogged with the dust1 and the sieve or screen is rendered useless4 ,among other materials which may be adopted for fine-grain contact beds1 broken saggars in the pottery districts1 or slag in the neighbourhood of ironworks1 are probably the next best1 but only if they are properly graded in the manner described above4 ,indeed the chief difficulty in securing this fine-grade material is the preparation and grading1 particularly where large quantities are required and the situation of the beds involves much handling of the material after it has been sifted4 ,it is1 however1 of such extreme importance to have it as fine as possible1 without including any dust1 that the stipulations in the specification with regard to this material should be made very clear and definite1 so that the contractor may make sufficient provision in his prices to enable him to comply with the specification in its strictest sense4 ,in addition to the bottom layer of floor-tiles and coarse material prescribed in the section relating to sub-drainage1 it will be necessary to provide an additional layer above this1 about #c inches in depth1 of a medium grade1 to support the very fine material and prevent it being washed through the interstices in the coarse bottom layer1 and special attention must be devoted to the method of distribution at the surface in order to avoid disturbance of the fine material4 ,illustration3 ,,fig4 #adj4--;,,automatic ,,apparatus ,,for ,,contact ,,beds4 ,automatic ,apparatus for ,contact ,beds4--,although contact beds can be operated by hand1 this involves continuous and regular supervision by a man1 and1 unless he is under strict control1 the proper cycle of operation may not be adhered to1 and the result will1 in that case1 not be satisfactory4 ,in the early days of contact beds1 several types of apparatus were designed for the purpose of operating these beds automatically1 so that the cost of manual labour would be reduced to a great extent1 and in addition1 the possibility of mismanagement avoided4 ,among these appliances1 one of the most widely known is that manufactured by ,messrs4 ,adams ,hydraulics1 ,limited2 and shown in ,fig4 #adj4 ,in small installations1 the low draught syphons described above in connection with dosing apparatus are used to give alternate fillings to pairs of contact beds4 ,where more than two beds are in use the automatic air-lock feed is used4 ,this consists of a cast-iron inverted ,u-pipe1 both legs of which are trapped1 either in self-contained castings or in separate chambers4 ,the sewage flows through one1 the others being charged with air4 ,when the sewage in the bed has reached the proper height it overflows into a small chamber in which a dome is fixed4 ,this dome is connected by means of an air-pipe to the cast-iron inlet feed1 and as the sewage rises in the chamber round the dome1 the air contained therein is forced up into the feed which it fills1 thus forming an air-lock1 which prevents the sewage from passing through and stops the supply to the bed4 ,at the same time that the feed is stopped by the transfer of air in the manner described1 the compression of the air in another small dome in the same pit has forced a water seal on the air-pipe leading from this dome to the feed in the next bed1 and thus liberates the air-lock in the feed of that bed and allows the sewage to flow to this in rotation4 ,the whole operation is then repeated with each bed in rotation1 the last bed in the series1 when full1 starting the feed in the first bed again4 ,these same feeds may be arranged to hold up sewage in a collecting or dosing tank1 so as to ensure the accumulation of sufficient sewage to fill each bed at one dose within a reasonable time4 ,illustration3 ,,fig4 #ada4--;,,contact ,,bed ,,apparatus4 ,in order to ensure that the sewage is held up in each bed for a suitable period for contact1 the outlet is provided with an automatic syphon1 which is arranged in such a way that the filling of the bed alone can start it4 ,when the bed is full1 the sewage flows through a pipe with an adjustable orifice into the timing pit4 ,when this pit is full1 the compression of the air in a small dome placed in the pit1 and connected to the syphon by means of an air-pipe1 releases the air in the syphon and allows it to start at the end of the desired period of contact4 ,a special feature of these syphons is that they are so arranged that after they have emptied the bed they continue in action as syphons1 taking the drainings from the bed1 however small in volume they may be1 and stopping off only when the bed commences to fill again1 thus ensuring a thorough draining of the material4 ,another special feature of this apparatus is that there are no moving parts1 the whole operation depending upon the transfer of air by means of the head of liquid4 ,it is important to note that by this apparatus the period of contact in any bed can be arranged for any particular length of time1 quite irrespective of the rate of flow of the sewage to the works1 and independent of the filling and emptying of the other beds in the series4 ,illustration3 ,,fig4 #adb4--;,,contact ,,bed ,,apparatus4 ,illustration3 ,,fig4 #adc4--;,,contact ,,bed ,,apparatus4 ,illustration3 ,,fig4 #adc;a4--,,contact ,,bed ,,apparatus4 ,another apparatus which has been used largely in the past is that supplied by the ,septic ,tank ,company1 ,ltd4 ,this apparatus is made in two forms1 illustrated in ,figs4 #ada and #adb4 ,the chief difference between the two types is that in the one case1 ,fig4 #ada1 the period of contact is controlled by the filling of the next bed1 and is thus dependent upon the rate of flow of the sewage1 while in the other case1 ,fig4 #adb1 the period of contact is 8timed0 for from one to two hours1 and is independent of the rate of flow of the sewage4 ,in both cases each set of gear is built up on its own bed-plate1 and comprises the inlet and outlet valves and the connecting pipes to and from the same4 ,the valves are of the simple spindle-type1 and are connected by rods to rocking levers and actuated by buckets or floats1 working in chambers or pits which are in communication with the different beds4 ,by means of overflows from the beds to the buckets1 and other devices1 the various portions of the gear are actuated in such a manner that they automatically fill the several beds in each set in regular rotation1 hold them full for contact1 and eventually discharge the treated liquid to the effluent drain4 ,full details of the method of operation can be obtained from the manufacturers1 who claim that the gear will work satisfactorily without attention other than the oiling of the bearings and joints every few weeks4 ,another type of automatic apparatus for contact beds is that manufactured by ,messrs4 ,j4 ,blakeborough and ,sons1 as used in the ,triple ,tank ,system of sewage treatment1 ,fig4 #adc4 ,in this case the beds are arranged in sets of three1 and the filling of each is effected by the overflow from the last bed filled1 the discharge being effected by the rising of the liquid in the last bed filled4 ,the apparatus consists broadly of a slide-valve controlling the outlet-pipe1 and connected by levers to floating cylinders located in separate chambers4 ,one chamber controls the opening and the other the closing of the valve4 ,the outlet is provided with a rising and falling arm1 which is connected by a lever to a balance float fixed in a chamber1 and coupled by means of a pipe to the float-chamber of another bed4 ,the method of operation is us follows3--,the tank effluent flows by gravitation to bed ,a1 the filtered effluent thus rising in outlet chamber ,a1 and also in the overflow chamber which is connected by pipes to outlet chamber ,a4 ,as soon as bed ,a becomes full1 the filtered effluent overflows into closing chamber ,a1 which is coupled by a pipe to opening chamber ,b1 and the floating cylinders in each case are raised1 with the result that the valve of bed ,a closes and the valve of bed ,b opens1 the liquid thus commencing to run on to bed ,b4 ,the same action as above is repeated when bed ,b is full1 and bed ,c is to be filled1 whilst bed ,c in turn is coupled to bed ,b1 so that the triple action is repeated over and over again so long as sewage continues to flow to the beds4 ,as bed ,a fills1 the liquid rises in outlet chamber ,a1 and1 this being coupled to float chamber ,c1 the liquid rises to a corresponding height in float chamber ,c4 ,some time elapses before the liquid rises to such a height in the float chamber as to sink the mouth of the outlet pipe below the surface of the liquid in the outlet chamber1 this space of time 7which can be regulated as desired7 representing the length of time that the bed is allowed to stand full before commencing to empty4 ,when the liquid has risen to a given height in float chamber ,c1 the balance float is raised1 this action tipping the lever and lowering the rising and falling outlet pipe in outlet chamber ,c1 thus drawing off the effluent from the top slowly1 and without disturbing the whole contents of the bed4 7,note3 ,bed ,c is assumed to be full74 ,after the liquid in the bed has been drawn off1 the rising and falling outlet pipe remains stationary at the bottom of the chamber until the next action takes place1 which is as follows3--,when bed ,a becomes full1 it is allowed to stand full until the liquid in bed ,b 7now filling7 has risen to a given height1 when it raises the balance float in the float chamber ,a in a similar manner as described above1 and thus empties the bed ,a1 at the same time emptying the float chamber ,c1 in which is fixed the balance float connected to the rising and falling outlet pipe of the bed ,c 7now standing empty71 thus raising the outlet pipe and rendering the bed again ready for use4 ,illustration3 ,,fig4 #add4--;,,contact ,,bed ,,apparatus4 ,illustration3 ,,fig4 #add;a4--,,contact ,,bed ,,apparatus4 ,messrs4 ,glenfield and ,kennedy1 ,ltd41 also manufacture apparatus for operating contact beds1 as shown in ,fig4 #add4 ,this arrangement of the apparatus delivers the sewage to six beds4 ,there are two valve boxes1 ,a1 internally divided into three compartments4 ,three sets of tube valves1 ,b1 on each valve box1 control the inlets to the several compartments of the valve box and also to the beds1 which are connected up to the valve boxes with suitable pipes4 ,as the sewage collects in the measuring chambers1 it raises the float ,c--the float chamber being in communication--which1 through the rack-and-pinion shown1 turns the shaft ,d4 ,to a sleeve1 ,e1 over the shaft ,d1 a hammer1 ,f1 is keyed1 while a stopper catch1 ,g1 is mounted freely4 ,keyed to the shaft ,d are lifting levers ,h and ,k4 ,the lever ,k lifts the hammer ,f to the vertical1 and1 being free to rotate with the sleeve ,e1 it falls and strikes on one of the copper buffers1 ,l1 in the turning plate ,m1 causing it to turn4 ,in like manner the stopper catch ,g is thrown over by the lifter ,h--a little in advance of the hammer--and1 resting on the stopper plate ,n1 drops into one of the notches1 ,o1 thus stopping the gear at the proper place4 ,the turning of plate ,n causes the roller lever ,p1 keyed to the vertical shaft ,q1 to rotate--through the agency of the mitre gearing and horizontal shaft--thus actuating the lever ,r1 and raising the tube valve ,b4 ,two valves are operated simultaneously1 one on each valve box4 ,the valves are held open by the levers ,p1 until1 the water being run off1 the weight of the float descending puts the gear in motion again--by returning the hammer to its original side--and moves the roller levers ,p off the end of the levers ,r1 thus allowing the tube valves ,b to close and the water to collect once again4 ,the force of the blow of the hammer as it strikes the buffer ,l can be regulated within certain limits1 for1 on the outer end of the sleeve ,e carrying the hammer1 a lever1 ,s is keyed1 which1 as it works in unison with the hammer1 and is attached to the piston of the swivel cataract adjustable oil cylinder ,t1 has the effect of cushioning the fall of the hammer4 ,another type of syphonic apparatus for contact beds is manufactured by ,messrs4 ,burn ,bros41 as shown in ,fig4 #ade4 ,in this case the primary filters are usually supplied with sewage from a collecting or dosing tank in which two or more discharge syphons are fixed1 or they may be filled from a supply channel under certain circumstances4 ,in the former case a syphon discharges immediately the collecting tank is full4 ,a 8,sequela0 relief apparatus is attached to each syphon1 and causes these to discharge alternately or in rotation4 ,the relief apparatus is divided into three compartments1 and depends for its working on the transference of oil1 of a special nature1 from one compartment1 ,a1 to another compartment1 ,c1 via compartment ,b1 in stages corresponding with the number of syphons under control1 each relief apparatus at the commencement being set a stage in advance of the one next to it4 ,after a syphon has discharged1 the oil which has been transferred to the compartment ,c in the relief apparatus is automatically returned to the compartment ,a1 and the apparatus is then ready for another series of operations4 ,thus the oil1 which is non-evaporative and non-freezing1 is used over again and again1 and as it does not come in contact with the sewage1 it remains quite pure and serviceable for years4 ,a discharge syphon is fixed to each filter1 and1 in order to ensure a proper period of contact of the sewage with the filtering material1 each syphon is provided with a 8,horometer0 relief apparatus4 ,this apparatus can be set to give a period of contact varying from twenty minutes to twenty-four hours4 ,the 8,horometer10 like the 8,sequela10 depends upon the transference of oil from one compartment to another1 but in this case only two compartments are necessary1 ,a and ,b4 ,as the filter fills1 the oil is forced1 by air pressure1 to rise in a vertical pipe from compartment ,a above the level of a regulating tap1 which is set to pass the oil into compartment ,b in the time determined upon for the contact of the sewage in the filter1 and as soon as the necessary quantity of oil has been transferred through the tap1 the syphon discharges4 ,after the syphon has discharged1 the oil is automatically returned from compartment ,b to compartment ,a1 and the apparatus is again ready for use4 ,no watertight brick chambers are required in the filter in connection with the apparatus1 thus effecting considerable economy in structural work4 ,it is only necessary to construct a screen in dry brickwork or perforated iron round the syphons to hold up the filtering material4 ,illustration3 ,,fig4 #ade4--;,,contact ,,bed ,,apparatus4 ,illustration3 ,,fig4 #ade;a4--,,contact ,,bed ,,apparatus4 ,the syphons manufactured by ,messrs4 ,george ,jennings1 ,ltd41 actuated by air-valves as described under the heading of 8,dosing ,apparatus10 can also be adapted for filling and emptying contact beds4 ,illustration3 ,,fig4 #adf4--;,,contact ,,bed ,,apparatus4 ,the ,enock apparatus for contact beds1 ,fig4 #adf1 manufactured by ,messrs4 ,a4 ,g4 ,enock and ,co41 ,ltd41 is a simple device working on the principle of the ball valve4 ,a float1 which takes the place of the ball1 is raised by liquid entering a pit1 which pit is outside the bed or tank which has to be emptied by the valve4 ,the valve is attached to a vertical rod in connection with a horizontal weighted lever1 at the other end of which the float is fixed4 ,when a tank is full1 it flows into the float chamber1 and the rise of the liquid in this pit lifts the float and opens the valve1 thereby allowing the contents of the tank to escape4 ,the float pit then slowly empties itself by means of a small outlet pipe1 and the valve closes so that the tank is ready to receive more liquid4 ,this apparatus can be arranged so as to fill a number of beds in rotation1 the inlet valve to each pit being either opened or closed as required by the overflow of liquid from each contact bed in turn4 ,the outlet valves to the contact beds are similar to those already described and if the first beds are filled in rotation1 no further connection between the apparatus in the lower beds will be required1 each valve working absolutely independently of the others4 ,the chief advantage claimed for this type of apparatus is1 that it can be adjusted so as to suit any required level of liquid in any particular bed4 ,,capacity ,,of ,,percolating ,,filters ,,and ,,contact ,,beds4 ,although this separate section is devoted to the question of calculating the capacities of percolating filters and contact beds1 it is mainly for the purpose of stating that it is impossible to formulate any rules which admit of general application4 ,it may reasonably be pointed out that this last statement is a truism1 and affords no assistance to those in search of information on the subject4 ,there is1 however1 so great a tendency in some quarters1 to rely upon results obtained in one place under certain conditions as a guide in designing a scheme in another place under possibly totally different conditions1 that it is impossible to repeat the statement in question too often4 ,in the first place1 long and practical experience is necessary to enable an engineer to come to a decision as to what are the conditions under which any particular scheme is to be carried out1 and which of them will have a bearing upon the methods to be adopted in the design of the works4 ,a careful study of the fifth report of the ,royal ,commission on ,sewage ,disposal1 will show that they assume over #gj different sets of conditions under which percolating filters and contact beds may be adopted4 ,the capacity of the filters required to produce the desired results will depend upon the strength of the sewage to be treated1 the type of tank adopted for the preliminary process of sedimentation1 the grade of material to be used1 the amount of fall available1 the final destination of the effluent1 and other factors1 all of which again may be affected by other circumstances1 which must of necessity be taken into consideration4 ,as the basis for calculating the capacity of filters may vary between #ae and #bjj gallons of the daily dry-weather flow per cubic yard of material1 it is evident that there is a wide margin for error1 and the only safe course to adopt is to allow for the worst possible conditions and thus provide a large margin of safety4 ,although the suggestions made in the fifth report of the ,royal ,commission with regard to the provision to be made under various sets of conditions may be taken as a guide1 to some extent1 it should be borne in mind that the figures given represent the minimum which should be allowed in each case1 and the only really safe guide in these matters is long practical experience of a large number of works under the greatest possible variety of conditions4 ,in order1 however1 to provide a rough guide for the purpose of making preliminary estimates1 it may be stated here that1 under ordinary conditions1 with sewage of average strength1 a properly designed preliminary process1 suitable material of medium grade1 and not less than #d feet deep for percolating filters1 it should be possible to produce an effluent which will not create a nuisance by providing-- 7a7 ,percolating filters1 at the rate of one cubic yard for every #hd gallons of the daily dry-weather volume1 or 7b7 ,contact beds1 at the rate of one cubic yard in each series for every #ef gallons of the daily dry-weather volume4 ,in other words1 the ratio of the cubic capacity of filter material to the daily dry-weather volume of the sewage for all ordinary purposes may be taken as-- 7a7 #b to #a for percolating filters4 7b7 #c to #a for contact beds4 ,,table1 ,,giving ,,the ,,ratio ,,of ,,the ,,total ,,cubic ,,capacity ,,of ,,percolating ,,filters ,,and ,,contact ,,beds ,,to ,,the ,,daily ,,dry-,,weather ,,volume ,,of ,,the ,,sewage ,,under ,,varying ,,conditions4 ,percolating ,filters ,strength of ,sewage ,strong ,average ,weak ,preliminary ,process4 ,grade of ,material 7,see pages #bc1 #bi74 ,coarse ,coarse ,coarse or ,fine or ,fine or ,fine medium medium medium ,detritus tanks #aabj -- #fgb -- #dbj -- ,septic tanks #cgc -- #bdj -- #afh #afh ,continuous flow settlement #cgc -- #bdj -- #afh #afh ,quiescent settlement #ccf #fgb #afh #bdj #abi #abi ,continuous flow chemical precipitation #beh #ccf #afh #baj #aab #jif ,quiescent chemical precipitation #afh #beh #abi #abi #jih #jhd ,contact ,beds ,strength of ,sewage ,strong ,average ,weak ,preliminary ,process4 ,number of ,series 7,see pages #bc1 #bi74 #a #b #c #a #b #c #a #b #c ,detritus tanks -- -- #fgb -- #fgb -- -- #ddb -- ,septic tanks -- -- #eji -- #ddb -- #bbdbed -- ,continuous flow settlement -- -- #eji -- #ddb -- #bbdbed -- ,quiescent settlement -- -- #cha -- #ccf -- #afh -- -- ,continuous flow chemical precipitation -- #eji -- -- #ccf -- #abf -- -- ,quiescent chemical precipitation -- #cij -- -- #bed -- #abf -- -- ,,key3 #a ,single #b ,double #c ,triple ,in the case of contact beds these figures give the cubic capacity of each series1 and they must be doubled or trebled respectively for double and triple contact4 ,both percolating filters and contact beds1 constructed on this basis1 would be capable of treating up to three times the dry-weather flow in times of storm4 ,having given the above method of calculation1 in a form not usually adopted in connection with sewage disposal1 and bearing in mind the misunderstandings which frequently arise in comparing the various methods in use at the present time in different countries1 it may be useful to set out in this form the figures which1 it is understood1 have been adopted by the ,local ,government ,board1 on the basis of the fifth report of the ,royal ,commission on ,sewage ,disposal1 as the minimum which they consider suitable under varying conditions4 ,in the ,table opposite1 the figures given represent the ratio which the cubic capacity of the filters bears to the daily dry-weather volume of the sewage1 whether it be in gallons1 cubic feet1 cubic metres1 vedros1 or any other term of measurement4 ,examples4--#a4 ,a daily dry-weather volume of #aj1jjj gallons of sewage1 of average strength1 is to be treated upon percolating filters of medium sized material1 after preliminary treatment in septic tanks4 #aj1jjj gallons #bdj #bd1jjj gallons #c1hdj cubic feet total cubic capacity of filters #b4 ,a daily dry-weather volume of #c1jjj cubic metres of weak sewage is to be treated upon single contact beds1 after preliminary treatment in continuous flow settlement tanks4 #c1jjj cubic metres #bbd #f1gbj cubic metres total cubic capacity of beds ,for the purpose of the above ,table1 the strength of the sewage is estimated according to the amount of oxygen absorbed from permanganate of potash in four hours1 as indicated in the fifth report of the ,royal ,commission as follows3-- ,parts per #ajj1jjj 8,strong0 sewage oxygen absorbed #ag to #be 8,average0 0 0 0 #aj to #ab 8,weak0 0 0 0 #g to #h ,a quick method of converting gallons into cubic feet is to multiply the gallons by the reciprocal #jaf4 ,this can be done rapidly 7frequently by mental calculation7 by multiplying the gallons by #d1 and the product again by #d1 and inserting the decimal point between the second and third figures from the right-hand side1 thus3-- #bd1jjj #d #if1jjj #d #chd1jjj #chdjjj cubic feet ,this is useful in calculating the capacity of tanks1 and for all similar purposes4 ,,storm-,,water ,,treatment4 ,in connection with ,sewage ,disposal ,works1 the term 8storm-water0 is generally understood to mean the extra volume which reaches the works in times of rainfall1 in excess of three times1 up to and including six times1 the average dry-weather flow2 so that the volume of storm-water for which provision should be made is equal to three times 7volumes7 the daily dry-weather flow4 ,prior to the publication of the fifth report of the ,royal ,commission1 it was usual to provide a rough straining filter for the storm-water1 or to reserve a portion of the land for the purpose of dealing with it by broad irrigation4 ,in either case the area of filter surface or land required was #a superficial yard for every #ejj gallons of storm-water 7,d4,w4,f4 #c_/ejj super-yards74 ,as the result of their investigations1 the ,royal ,commission came to the conclusion that 8storm-water0 filters1 as generally constructed under these conditions1 were useless for the purpose for which they were required1 and this confirmed the views of most engineers of experience4 ,where suitable land can be secured for the purpose1 and arranged in such a manner that it is reserved solely and entirely for treating the storm-water1 this method may still be adopted4 ,if this is not possible1 stand-by tanks may be constructed for the purpose of receiving the storm-water4 ,these tanks are to be not less than two in number1 and should have a total capacity of not less than one-quarter of the average daily dry-weather flow4 ,the only overflow at the outfall works from which storm-water may be discharged direct to the stream1 or other final effluent outlet1 must be from these stand-by tanks1 and it should not come into operation until these tanks are full4 ,having regard to these recommendations1 it is necessary in every scheme to provide at least two special storm-water stand-by tanks1 with a total capacity of ,d4,w4,f42 and the drawing1 ,fig4 #adg1 illustrates a simple method of constructing these4 ,in this case the inlets are in the form of weirs1 running the full width of the tank1 so that if the channel leading to these tanks is in communication with1 and at the same level as1 the inlets to the detritus tanks1 and the latter are provided with slotted doors 7see ,fig4 #aj1 page #ai71 the weir at the inlets to the stand-by tanks will act as the actual storm-overflow1 and1 being of considerable length1 the maximum height to which the water will rise in passing over this weir will be very small1 and will thus have very little effect upon the rate of flow to the sedimentation tanks4 ,as the only overflow discharging direct to the stream must be from these tanks1 and must only come into operation when they are full1 the outlet is also constructed in the form of a weir discharging into a channel from which a pipe would be laid to the stream4 ,a further requirement in connection with these tanks is that they should always be kept empty1 ready to receive the excess of storm-water at any time4 ,from this it is evident1 that these tanks must be emptied after each heavy shower or storm which increases the rate of flow of sewage to the works beyond three times the dry-weather flow4 ,unfortunately1 no directions are given as to the manner in which this is to be accomplished4 ,in the absence of any definite statement to the contrary1 it might be inferred that1 after the overflow from these tanks has ceased1 their contents may also be discharged direct to the stream4 ,as1 however1 this would necessitate outlets at or near the bottom of the tanks1 there would appear to be a possibility of the suspended matters deposited in the tanks being discharged to the stream--the very thing the tanks are designed to prevent4 ,with such an arrangement1 also1 there will be a risk of the man in charge of the works1 either wilfully or by an oversight1 leaving the outlets at the bottom of the tanks open1 and thus permitting the storm-water to pass direct to the stream without the settlement which it is anticipated by the ,royal ,commission 7,fifth ,report1 page #bcc1 par4 #ceb7 will be provided for all storm-water arriving at the works4 ,illustration3 ,,fig4 #adg4--,,storm-,,water ,,stand-,,by ,,tanks4 ,it is obvious that these tanks must be emptied after every heavy shower or storm1 and that facilities must be provided both for drawing off the supernatant water and for removing the deposit which will accumulate at the bottom4 ,in the author's opinion1 the only safe method is to provide floating arm outlets for the supernatant water1 and to discharge this to land or to a special filter for further treatment1 or1 better still1 to pump it up to the detritus tanks to be treated again with the ordinary sewage4 ,in schemes where the whole of the sewage is pumped at the works1 the contents of these storm-water stand-by tanks should certainly be discharged into the pump-well1 as this would not involve the provision of special pumping plant4 ,with regard to the sludge from these tanks1 this should be drawn off by means of special outlets1 and dealt with on sludge draining beds in the manner previously described 7page #hc74 ,the difficulties which frequently arise in designing suitable and convenient methods of dealing with storm-water1 render it desirable that very careful consideration should be given to the question as to whether it would not be more satisfactory1 from the point of view of both economy and efficiency1 to omit the stand-by tanks1 and increase the capacity of the filters required to deal with the ordinary sewage1 to such an extent that they will be capable of dealing with the whole volume of sewage and storm-water combined up to six times the dry-weather flow1 and thus obviate the necessity for any storm-overflow at all at the outfall works4 ,if this idea were universally adopted1 it would necessitate greater care in the construction of any storm-overflow required on the line of the outfall sewer itself before it reaches the works1 but there are 7or should be if the sewers were properly constructed7 so few cases where the excess of flow1 even during the heaviest rainfall1 ever reaches six times the dry-weather flow1 that the extra cost involved cannot be considered excessive if the greater certainty of securing satisfactory results at all times is taken into consideration4 ,,measuring ,,apparatus4 ,in recent years the provision of proper means of measuring and recording the flow of sewage at disposal works is becoming more general1 but there are still a very large number of works at which it is impossible to obtain any trustworthy information as to the volume of sewage treated4 ,as long as all works smoothly1 and there is no trouble with the effluent1 it is considered superfluous to trouble about the quantity of the liquid which passes through4 ,when1 however1 difficulties arise1 and it becomes necessary to investigate the cause of the trouble1 it is of the utmost importance to be in a position to ascertain the daily volume of the sewage arriving at the works and the variations in the rate of flow1 as well as the quantities dealt with by each separate tank and filter4 ,it is also of great assistance1 in making investigations at such times1 to have a definite record of the volumes treated day by day during the preceding six months2 indeed the possession of a complete record of the daily flow of sewage over the whole period during which a sewage works has been in operation1 is a valuable asset not only to those responsible for the works themselves but also to the authorities who control the streams and watercourses1 and to investigators in search of information to be used for the public benefit4 ,the initial cost of suitable measuring and recording appliances is not excessive1 but1 when once the works are completed and in good working order1 the local surveyor or manager has great difficulty1 and usually finds it impossible1 to persuade his committee that the outlay is justified4 ,it is1 therefore1 desirable that engineers should in all cases make provision for such apparatus in the contract for the construction of the works1 and thus make sure that it will be available when required4 ,illustration3 ,,fig4 #adh4--;,,gauge ,,weir ,,penstocks4 ,various types of measuring appliances are in use4 ,among these the simplest is the gauge weir penstock ,fig4 #adh1 manufactured by ,messrs4 ,adams ,hydraulics1 ,ltd41 from which the depth of water flowing over the weir can be observed at any time4 ,this1 however1 does not provide a record of the volume flowing at all times4 ,for this purpose the same firm supply several types of recorders1 among which the simplest is the type shown in ,fig4 #adi4 ,this is supplied with #bd-;hour or #g-;day movement1 and charts which register the volume in gallons per minute1 per hour1 or per #bd hours4 ,illustration3 ,,fig4 #adi4--,,recording ,,apparatus4 ,another measuring apparatus is that supplied by ,messrs4 ,george ,jennings1 ,ltd41 ,fig4 #aej4 ,this consists briefly of a hollow copper float attached to a brass rod1 which is carried up through a hollow column into the indicator box provided with a glass hinged door4 ,the brass rod is provided with pointers1 which move up and down with the rods and indicate the water level4 ,illustration3 ,,fig4 #adi;a4--,,volume ,,recorder4 ,messrs4 ,george ,kent1 ,ltd41 supply a large number of various types of recorders and measuring instruments1 including the well-known 8,venturi0 meter and others actuated by floats to indicate the discharge over a weir4 ,the ,venturi meter type of measuring apparatus adapted for sewage1 is shown in ,fig4 #aea4 ,in this case the ,venturi tube may form part of the ordinary supply pipe1 or it may be fitted in a chamber built in the supply channel1 the tube connected through the chamber with its ends terminating in the channel at either side4 ,this measuring apparatus may be fitted with the following types of recorders4 ,a diagram only1 counter only1 or combined counter and diagram in one instrument4 ,the recorder may be placed in any convenient position within a thousand feet of the meter tube4 ,illustration3 ,,fig4 #aej4--,,measuring ,,apparatus4 ,illustration3 ,,fig4 #aea4-,,the 8,,venturi0 ,,meter4 ,illustration3 ,,fig4 #aeb4--,,measuring ,,apparatus4 ,several types of measuring apparatus are manufactured by ,messrs4 ,glenfield and ,kennedy4 ,one of these is illustrated in ,fig4 #aeb4 ,this consists of an apparatus for recording the volume of water or sewage flowing over a weir1 a chart being revolved by clockwork1 and the volume indicated by a pen actuated by a float and cord working over pulleys4 ,this instrument can be fitted with cam and pen carriage to show the rate of discharge on the chart 7#bd hours or #g days71 in gallons of cubic feet per minute over a ,v-notch1 rectangular weir1 or in an open channel of known dimensions4 ,it is claimed that by simply taking the area of the diagram1 the total discharge for any period can be ascertained much more quickly and more correctly than from a diagram simply giving the height flowing over the weir4 ,a somewhat novel form of apparatus1 recently introduced by ,messrs4 ,adams ,hydraulics1 ,ltd41 for measuring the flow of sewage in a channel1 consists of a water-wheel by means of which the velocity of the flow is registered4 ,in order to maintain the paddles of the wheel at a uniform depth below the surface of the liquid1 the wheel is carried upon a shaft supported by two floats provided with vertical guide rods working in brackets attached to the sides of the channel4 ,by this means the whole of the apparatus rises and falls with the liquid in the channel4 ,the wheel-shaft is provided with a bevel-toothed wheel1 which engages with another similar wheel attached to a flexible shaft1 and this drives a set of geared wheels similar to a flush-tank counter1 which thus record the number of revolutions made by the paddle-wheel4 ,,sterilisation ,,of ,,sewage ,,effluents4 ,it has been recognised in many quarters that1 although it is possible by modern methods of sewage disposal to secure a high degree of purification from a chemical point of view1 it may be necessary in certain cases to take steps to remove the large numbers of bacteria present in all such effluents4 ,experiments have been made which demonstrate that1 when a pure culture of some specific organism is added to a sewage in a sufficiently large quantity1 it may pass through the tanks and filters1 and appear in the final effluent4 ,this result is not necessarily a conclusive proof that the bacteria in sewage effluents are dangerous1 as the experiments do not represent normal practical conditions4 ,on the other hand1 it is true that1 in ordinary practice1 sewage effluents contain large numbers of ,b4 coli1 which is admittedly of intestinal derivation1 and although this bacillus is not a disease organism itself1 its survival in an effluent is considered an indication of the presence of sewage matter1 and consequently of the possibility of the survival of any pathogenic germs which may be present in the crude sewage4 ,on this basis1 scientists argue that sewage effluents are potentially dangerous--that there is a possibility of the pollution of drinking-water or shell-fish by the bacteria present in sewage effluents4 ,this being so1 it is evident that an additional process will1 in some cases1 be required to remove the bacteria1 and in a few cases sand filters have been provided for this purpose4 ,these1 however1 involve a comparatively high initial expense1 and a considerable annual outlay for maintenance1 and in some quarters it is considered that sterilisation may possibly be a means of securing the desired result at less cost1 and with a higher percentage of removal of bacteria1 and consequently with a higher degree of safety4 ,it is true that a number of scientists1 in replying to a question which was submitted to them on this subject by the ,royal ,commission on ,sewage ,disposal1 stated that in their opinion sterilisation was impracticable1 but this was in the year #aijc1 and there is good reason for assuming that if the same question were put to the same men to-day1 the replies would in many cases be modified1 if not entirely different4 ,practical experiments in the sterilisation of sewage effluents have been few and far between in this country1 but in the ,united ,states of ,america a large number of reliable experiments under varying conditions have been made1 and the results published4 ,from these it is evident that sterilisation is not only possible1 but economically practicable4 ,unfortunately1 both in ,america and elsewhere1 attempts were made to sterilise crude sewage and tank effluents1 and the results of these experiments were so unsatisfactory1 both in efficiency and cost1 that they gave the impression that sterilisation was impracticable4 ,in the opinion of the author1 sterilisation should be restricted to the destruction of living organisms1 and should only be used in the case of liquids with a high degree of chemical purity1 and a low content of matters in suspension4 ,it is quite possible at the present time to produce sewage effluents which comply with these conditions1 by means of properly designed1 constructed and managed sewage disposal works1 as long as these include suitable effluent settling tanks for the removal of the solids in suspension4 ,effluents which comply with the provisional standard suggested by the ,royal ,commission1 and drinking-water supplies which are very slightly polluted1 would be very suitable4 ,a number of different methods of sterilisation have been tried1 but so far as the existing knowledge of the subject extends1 the application of chlorine in one form or another is generally admitted to be the most efficient and economical process4 ,the chlorine may be applied in the form of a solution of chloride of lime1 or as a hypochlorite of sodium1 or of magnesium4 ,the solution of chloride of lime may be prepared by the sewage works manager1 but this necessitates a considerable amount of care and knowledge in order to secure the correct strength at all times1 and it is1 of course1 essential that the chloride of lime itself should always be of a known strength4 ,the hypochlorite of sodium may be produced chemically1 and this can be purchased of known strength from chemical manufacturers4 ,for large volumes of sewage effluent1 however1 it will probably be found most economical to utilise an electrically produced hypochlorite of sodium1 as this can be prepared on the works as and when required1 of a uniform strength1 and at a comparatively low cost4 ,in the case of the ,digby process1 briefly stated1 this consists in passing an electric current through a solution of sodium chloride1 with the result that the sodium chloride is broken up into its component parts1 and chlorine is liberated at the positive pole1 while sodium is deposited at the negative pole4 ,the sodium and the chlorine are then allowed to recombine in the form of hypochlorite1 and this solution is then ready for application to the liquid to be sterilised4 ,other processes are similar in principle but vary in detail4 ,illustration3 ,,fig4 #aec4--,,the ,,digby ,,meridioniser4 ,this process naturally involves the use of an electric current and an apparatus for producing the hypochlorite4 ,of the latter there are several on the market1 and an illustration of the ,digby ,meridioniser1 which is manufactured and supplied by ,messrs4 ,adams ,hydraulics1 ,ltd41 is given in ,fig4 #aec4 ,the particular feature of this apparatus consists in the manner in which the re-combination of the anode and cathode products are secured4 ,instead of the re-combination taking place in the main body of the electrolyte1 it can only take place in the special porous compartment enclosing the electrodes4 ,the re-combination may take place in either the anode or the cathode compartment1 the products of the one compartment being conveyed to the other compartment4 ,thus the caustic hydrate from the cathode cells flows by gravity into the anode compartment1 the two compartments being connected by a glass pipe4 ,fresh water or water containing an excess of alkali is run into the cathode cell4 ,this process gives hypochlorite solution of low saline content1 the only salt present in the resultant liquor being that due to diffusion1 depending upon the porosity of the closely covering compartment walls1 or upon such a reaction as that covered by the ,blount hypothesis4 ,a cross-section of this apparatus is shown at ,fig4 #aec1 in which ,a is the positive lead2 ,,bb negative leads1 ,c outflow1 ,d inflow1 ,,ee cathodes1 ,f anode4 ,another machine is that supplied by ,messrs4 ,oxychlorides 7#aijg71 ,limited4 ,this machine consists essentially of a graphite anode of circular cross-section 7except as to about #d in4 at the top1 which is left open for the free escape of gases evolved during the electrolysis71 and within it a metallic cathode of smaller circular cross-section4 ,the annular space between the anode and cathode is filled with a solution of common salt1 or with sea-water1 through which a current is passed from a low-potential dynamo4 ,in either case the ultimate result is to obtain some of the chlorine of the salt in an active or available form1 the only difference being that in the case of using strong salt solution1 a concentrated form of available chlorine may be obtained1 while with sea-water a weaker solution results4 ,where sea-water is readily obtainable it is naturally more economical to make use of it1 and to employ the larger volume of less concentration2 while where sea-water is unobtainable and salt is expensive1 or where chlorides in the effluent are objected to1 it is more advantageous to prepare concentrated solutions1 and to dilute them when required for use4 ,this machine is made in various sizes to suit varying conditions4 ,it was used by the ,royal ,commission on ,sewage ,disposal in connection with their experiments at ,guildford1 referred to in their ,report of #aijh1 pages #aih to #bja4 ,electrolytic hypochlorite of magnesium is being produced daily1 by the ,borough of ,poplar1 for use as a disinfectant4 ,the highly effective qualities of this solution1 as well as the low cost of production1 makes it a very valuable disinfectant1 and for the results obtained every credit is due to ,dr4 ,f4 ,w4 ,alexander1 the ,medical ,officer of ,health1 who initiated the scheme1 and to whose unbounded energy and enthusiasm the success of the work is due4 ,this solution is1 of course1 equally suitable for the sterilisation of sewage effluents4 ,the cost of production of this solution1 of an average strength of from #de to #e grammes of available chlorine per litre 7#de to #e per cent4 solution71 is estimated at under one penny per gallon4 ,the apparatus in use at ,poplar has been supplied by the ,farringdon ,engineering ,co41 and an illustration of the plant is shown in ,fig4 #aed4 ,illustration3 ,,fig4 #aed4--;,,electrolytic ,,hypochlorite ,,of ,,magnesium ,,plant4 ,it consists of four cells1 each containing ten elements1 consisting of one positive and two negative plates4 ,the positive plates consist of thin platinum wire1 wound upon slate slabs1 and the negative electrodes are of zinc4 ,the four cells are placed one above the other1 so that the liquid passes through from one to the other by gravitation4 ,the feed-tank at the top contains a solution of sodium chloride and magnesium chloride1 and is fitted with a glass gauge to indicate the amount of solution in the tank4 ,from this tank the solution passes through a small ball-valve cistern1 so as to maintain a constant rate of flow4 ,the feed-tank is also provided with a plate1 operated by a chain carried over to the outside of the tank1 by means of which the liquid to be electrolysed can be stirred from time to time1 so as to secure a uniform strength of solution4 ,the solution passes through the four electrolysers in series1 being subjected to the action of a regulated current of #ae to #ag amperes at #bcj to #bej volts1 being #eg to #fb volts per cell4 ,after the electrolysed solution leaves the last cell it runs into a small tank1 where a fixed amount of hydroxide of magnesium is mixed with it1 and it is claimed that by this means the solution is rendered stable1 a quality which should be of much value where the solution has to be stored for any length of time4 ,the question as to what is the most suitable sterilising agent to use under certain conditions1 and in what proportion it should be added to the sewage effluent1 is a matter for the chemist and biologist4 ,the method of application is1 however1 the duty of the engineer4 ,as in the case of other chemicals1 there are two ways in which it may be applied4 ,the solution may be added to the sewage effluent in equal doses of varying strength1 or in varying doses of equal strength4 ,there is a third method1 involving the variation of the dose and the strength of the solution1 but while this is not impossible it is probably not practical4 ,the chief difficulty to be overcome is the variation of both the rate of flow and the strength of the sewage1 and the most practical solution is to prepare the sterilising agent of a uniform strength1 and vary the doses in direct proportion to the flow of the effluent1 the minimum dose being sufficient for the maximum strength of the sewage4 ,this method was adopted by the author in the case of a small scheme of sewage disposal1 which he prepared for a place where the only outlet for the final effluent was a discharge over an area of chalk subsoil1 from which the water supply of a large town is drawn4 ,in this case1 he designed a simple apparatus which does not involve any special appliances1 and which would be quite satisfactory for ordinary practical purposes4 ,a new apparatus for the purpose in question has1 however1 recently been introduced by ,messrs4 ,nixon and ,mannock4 ,as will be seen from the illustration1 ,fig4 #aee1 it is based upon the application of the ,venturi principle1 and involves the use of a ,venturi tube1 as previously described under the heading of 8,measuring ,apparatus40 ,in fact1 the same ,venturi tube can be utilised to serve both for measuring the flow of the effluent1 and for applying the sterilising agent in direct proportion to the flow of the effluent4 ,illustration3 ,,fig4 #aee4--,,nixon ,,and ,,mannock',s ,,apparatus ,,for ,,injecting ,,chemical ,,solution4 ,the apparatus consists of a cylinder ,c1 the top of which is connected by means of a pipe fitted with a three-way cock to the 8,upstream0 end of the tube ,a4 ,a similar connection is made from the bottom of the cylinder to the 8throat0 ,b4 ,a piston of the type used in the ,kent ,standard ,water ,meters1 and provided with a counterbalance weight1 works in the cylinder by means of the difference of the pressure on the two sides of the ,venturi tube4 ,the chemical solution 7e4g4 a #e per cent4 solution of chlorine7 is supplied to the underside of the piston1 and the pressure on the upper side of the piston being greater than the pressure on the underside1 the chemical is forced down by the piston and injected through the injection tube and regulating valve into the effluent at the 8throat0 of the ,venturi tube4 ,as the flow of the effluent through the ,venturi tube produces a difference of pressure which varies as the square root of the velocity1 the rate of injection will also vary in the same proportion4 ,the injection is thus in exact proportion to the flow1 and any variation of the flow will automatically cause a corresponding variation in the rate of injection4 ,when the chemical re-agent is exhausted1 the piston will be at the bottom of the cylinder1 and the pointer at zero4 ,in order to recharge the cylinder with the chemical1 the three-way cocks must be reversed by means of the hand lever1 thereby cutting off pipes ,a and ,b1 and simultaneously connecting the top of the cylinder to the waste pipe1 and the bottom to the supply from the chemical storage tank1 which is fixed at such a height that the head will rapidly force the piston up and re-fill the cylinder with the chemical4 ,the three-way valves are then reversed1 and the apparatus is again in full working order4 ,the apparatus shown is applicable to the treatment of #ajjj gallons per hour1 and will only need recharging once per day of #bd hours4 ,a feature of this apparatus is that it is self-starting1 and should the flow cease1 the injection will also automatically stop1 the static head on both sides of the piston being equal4 ,there is absolute immunity from danger or over-injection of the chemical by this system1 and this is a valuable factor in the treatment of potable water4 ,where absolutely necessary1 the same firm can supply a de-chlorinating apparatus4 ,by means of the indicator1 the works manager is constantly informed of the exact amount of chemical injected1 and the scale readings can be compared with those of a ,venturi ,meter operated by the same ,venturi tube4 ,this apparatus can be supplied of a larger size1 and provided with automatic recharging gear for larger installations4 ,whatever method may be adopted for applying the sterilising agent1 it is essential in all cases to have a storage tank to receive the mixture in order to provide time for the chemical to have full effect4 ,so far as can be ascertained at present1 a storage capacity equal to one hour's flow of the liquid to be sterilised will be sufficient under ordinary circumstances1 but provision should be made for thoroughly mixing the chemical with the effluent and for drawing off any deposit which may occur in the tank without interfering with the normal working of the plant4 ,although the present volume is devoted entirely to the disposal of sewage1 it may be stated here that in the matter of sterilisation1 the suggestions that have been made apply with equal force to drinking-water supplies4 ,where the water contains a considerable amount of matter in suspension1 it would be advisable to provide means for ample storage and settlement before passing it through the sterilising plant4 ,note4--,an apparatus for the injection of chlorine solutions for the purpose of sterilising sewage effluents and drinking water has recently been brought out by the ,candy ,filter ,co41 ,ltd41 and has for some months been in practical operation1 dealing with #bjj1jjj gallons of river water per day for an important municipal waterworks in the country4 ,in this case the installation includes a de-chlorinating process1 and it is stated that the results of tests in actual work show that the sterilised water contains neither ,b4 coli nor free chlorine4 ,,index ,,page 8,acme0 spray nozzle1 #aea 8,adams-,cutler0 distributor1 #ace 8,aerat0 distributor1 #ade ,apparatus for contact beds1 #bje 0 for dosing tanks1 #afg 0 for measuring flow1 #bcb 0 for percolating filters1 #ajf 0 for sludge removal1 #dj 0 for sterilisation1 #bdb ,auto-mechanical syphons1 #afh1 #afi1 #ahj ,birmingham fixed spray1 #aee ,candy-,whittaker bacterial tank1 #fj 0 0 distributors1 #ajf ,capacity of contact beds1 #bbb 0 of detritus tanks1 #bc 0 of effluent settling tanks1 #ahb 0 of percolating filters1 #bbb 0 of sedimentation tanks1 #bi 0 of storm-water tanks1 #bbg 8,capillary trough0 distributor1 #adf 8,carlton0 adjustable fixed spray1 #aeb 8,carlton0 distributor1 #abc 8,carlton rotor0 distributor1 #aba ,chemical mixers1 #gb ,cleaning gear for spray holes1 #aai1 #abb1 #abe 8,coleman0 dosing valve1 #afh ,columbus fixed spray1 #aee ,contact beds1 #ahi 0 0 apparatus for1 #bje 0 0 capacity of1 #bbb 0 0 filling material for1 #bjc 0 0 general design of1 #aij 0 0 methods of construction of1 #aif 0 0 0 of distribution on1 #aii 0 0 method of operation of1 #aia 0 0 necessity for testing1 #aih 0 0 sub-drainage of1 #bja 8,cresset0 distributor1 #aaj ,decanting valve1 #di ,detritus tanks1 #bc 0 0 capacity of1 #bc 0 0 ,dortmund type of1 #be 0 0 sludge scraper for1 #bg ,dibdin1 ,w4 ,j41 #fh1 #ahi ,digby meridioniser1 #bdc ,disc sprays1 #aee1 #aeg ,distribution by flooding filters1 #aeg1 #ahf 0 methods of1 #ajd ,distributors1 #ajf 0 cleaning gear for spray holes of1 #aai1 #abb1 #abe 0 fixed1 #adc 0 power-driven1 #abi1 #adj 0 revolving1 #ajf 0 travelling1 #ach ,dortmund tanks1 #be1 #ea1 #eb ,dosing apparatus1 #aff 0 tanks1 #afb 0 0 disadvantages of1 #afj 0 0 necessity for1 #aei ,drainage of filters and beds1 #ij1 #bja ,ducat filter1 #add ,effluent settling tanks1 #ahb ,elliott and ,brown1 #ei 8,facile0 distributor1 #aai ,feed channels1 #afc 8,fiddian0 distributor1 #abg1 #ach ,fieldhouse tank1 #fe ,filtering material1 #aja 0 0 grading of1 #ajc1 #bjd ,fine-grain filters1 #ahe ,fixed distributors1 #adc 0 sprays1 #adg ,floating arm1 #dh ,floor-tiles1 #ia ,gauge weir penstocks1 #bcc ,grading of material1 #ajc1 #bjd ,gravity disc sprays1 #aee1 #aeg ,grit chambers 7see also ,,detritus ,,tanks71 #bc ,haller and ,machell1 #ade 8,hanley0 distributor1 #adj 8,hartley0 distributor1 #acj 8,hodgson0 distributor1 #abg ,humus pits1 #ahb ,hydro-extractor for sludge1 #ha ,hydrolytic tank1 #eb ,hypochlorite solutions1 #bdb--bdg ,imhof tank1 #eg ,intermitting valves 7see ,,dosing ,,apparatus7 8,kessel0 tank1 #fc ,lowcock1 ,s4 ,r41 #ea ,low-draught syphon1 #afg ,massachusetts ,institute of ,technology1 #aee ,material for filters and beds1 #aja1 #ahe1 #bjc ,measuring apparatus1 #bcb ,non-septic cylinder1 #fa ,percolating filters1 #he 0 0 aeration of1 #hf 0 0 capacity of1 #bbb 0 0 distributors for1 #ajf 0 0 floor-tiles for1 #ia 0 0 floors for1 #hh 0 0 general design of1 #he 0 0 material for1 #aja 0 0 methods of distribution on1 #ajd 0 0 0 of feeding1 #aei 0 0 planning of1 #ih 0 0 sprinklers for1 #ajf 0 0 sub-drainage of1 #ij 0 0 types of construction of1 #hg 0 0 walls for1 #ie ,ponding valve1 #agh ,power-driven distributors1 #abi1 #adj ,precipitation tanks1 #dg ,preliminary processes 7see ,,tanks1 also ,,slate ,,beds7 ,recording apparatus1 #bcd--bci ,revolving distributors1 #ajf ,royal ,commission on ,sewage ,disposal1 recommendations1 #c1 #af1 #bc1 #bi1 #cb1 #ahb1 #bbd1 #bbf1 #bbg ,ryder1 ,e4 ,e41 #ic ,salford fixed spray1 #aee ,sand-filters1 #ahe 8,scott-,moncrieff0 distributor1 #acj ,screens1 #c 0 bars for1 #d 0 for deep sewers1 #g 0 mechanical1 #g 0 0 rake1 cleaning gear for1 #ab1 #ad 0 rotary1 #e 0 simple1 #c 8,separator0 tank1 #fe ,sewage mixers1 #gc ,shone and ,ault1 #ec 8,simplex0 distributor1 #abe ,skegness tank1 #ei ,slate beds1 #fg 0 slabs and blocks1 #fh1 #ib ,sludge disposal1 #ga 0 draining beds1 #hc 0 drying apparatus1 #ha 0 presses1 #ge 0 pressing plant1 complete installation1 #gg 0 removal1 #be1 #bh1 #ce1 #ga 0 0 apparatus for1 #bg 0 0 elevators for1 #dj1 #da1 #db 0 0 well for1 #ch ,spray jets1 #adg ,sprinklers1 #ajf ,stand-by tanks for storm water1 #bbi ,sterilisation of sewage effluents1 #bdj ,sterilising solutions1 #bdb 0 0 apparatus for the manufacture of1 #bdb--bdg 0 0 0 for the injection of1 #bdg--bej 8,stoddart0 distributor1 #adb ,storm-water overflow1 diverting plate for1 #ag 0 0 fixed weirs1 #ag 0 0 floating weir1 #ba 0 0 movable weirs1 #ba 0 0 swinging syphon for1 #ba 0 0 weirs1 #af 0 tanks1 capacity of1 #bbg 0 treatment1 #bbg ,strength of sewage1 #bbf ,supply pipes1 #afc 8,sypho-jet0 distributor1 #aaj ,,tanks1 #bi 0 ,candy-,whittaker1 #fj 0 capacity of1 #bi 0 circular1 #be1 #ea--ei1 #fj1 #fa1 #ff 0 continuous-flow settlement without chemicals1 #bi1 #cb 0 0 0 0 with chemicals1 #bi1 #cb1 #dg 0 decanting valve for1 #di 0 detritus1 #bc 0 ,dortmund type1 #be1 #ea1 #eb 0 ,fieldhouse1 #fe 0 floating outlet for1 #dh 0 hydrolytic1 #eb 0 ,imhof1 #eg 0 inlets and outlets for1 #dj--dg 0 0,kessel0 type1 #fc 0 non-septic1 #fa 0 precipitation1 #dg 0 quiescent settlement without chemicals1 #bi1 #cb 0 0 0 with chemicals1 #bi1 #cb 0 rate of flow through1 #cd 0 rectangular1 #cc1 #cf1 #cg1 #dc--ej 0 roofs for1 #ci 0 0separator01 #fe 0 septic1 #bi1 #cb 0 ,skegness1 #ei 0 storm-water1 #bbi ,taylor1 ,w4 ,gavin1 #aje ,travelling distributors1 #ach ,travis1 ,w4 ,o41 #eb ,trays and troughs1 #adc 8,triple tank0 system1 #ade 8,venturi0 meter1 #bcg ,walls of filters1 #ie ,waterbury fixed sprays1 #aee ,watson1 ,j4 ,d41 #ic1 #acj ,weirs1 fixed volume1 #ba 8,whirl0 spray jet1 #adi ,willcox and ,raikes1 #di1 #if1 #ace ,,manufacturers ,,of ,,appliances ,adamsez1 ,ltd4 ,adams ,hydraulics1 ,ltd4 ,adamson1 ,d4 and ,co4 ,albion ,clay ,co41 ,ltd4 ,ames-,crosta ,sanitary ,engineering ,co41 ,ltd4 ,blakeborough1 ,j4 and ,son1 ,ltd4 ,burn ,bros4 ,carlton ,engineering ,co4 ,enock1 ,a4 ,g4 and ,co41 ,ltd4 ,w4 ,e4 ,farrer1 ,ltd4 ,farringdon ,engineering ,co4 ,glenfield and ,kennedy1 ,ltd4 ,goddard ,massey and ,warner4 ,ham ,baker and ,co41 ,ltd4 ,harriman1 ,w4 and ,co41 ,ltd4 ,hartley1 ,causton and ,richmond4 ,george ,jennings1 ,ltd4 ,johnson1 ,s4 ,h4 and ,co41 ,ltd4 ,george ,kent1 ,ltd4 ,birch ,killon and ,co4 ,manlove1 ,alliott and ,co41 ,ltd4 ,mansfield1 ,h4 ,r4 ,mather and ,platt1 ,ltd4 ,naylor ,bros4 ,nixon and ,mannock4 ,oxychlorides 7#aijg71 ,ltd4 ,patent ,automatic ,sewage ,distributors1 ,ltd4 ,septic ,tank ,co4 ,smith1 ,john and ,co4 ,stiff1 ,c4 ,l4 ,stoddart1 ,f4 ,w4 ,stott1 ,s4 ,s4 and ,co4 ,whitehead and ,poole4 ,wolstenholme1 ,j4 and ,co4 ,,london3 ,,printed ,,by ,,william ,,clowes ,,and ,,sons1 ,,limited1 ,,great ,,windmill ,,street1 ,w41 ,,and ,,duke ,,street1 ,,stamford ,,street1 ,s4,e4 ,,advertisments4 ,,the ,,septic ,,tank ,,company1 ,,ltd4 #e ,victoria ,street ,,westminster ,for the ,,most ,,efficient ,,and ,,up-,,to-,,date ,,sewage ,,plant ,,of ,,every ,,description4 ,s4 ,h4 ,,johnson ,co41 ,ltd4 ,,sludge ,,pressing ,,machinery ,,sludge ,,filter ,,presses ,,with ,,patent ,,pyramid ,,drainage ,,surfaces1 ,,ratchet ,,capstan ,,tightening ,,gear1 ,,also ,,patent ,,hand ,,hydraulic ,,closing ,,gear1 ,,patent ,,hydraulic ,,opening ,,gear4 ,,sludge ,,forcing ,,rams ,,ordinary ,,or ,,automatic ,,system4 ,,our ,,twin ,,principle ,,saves #ej ,,air ,,consumption4 ,,air ,,compressors ,,single1 ,,or ,,two ,,stage1 ,,horizontal ,,steam ,,and ,,belt ,,driven ,,or ,,for ,,attachment ,,to ,,oil ,,or ,,gas ,,engines4 ,,vertical ,,high ,,speed ,,for ,,electric ,,drive4 ,,press ,,cake ,,disintegrators ,,pneumatic ,,lime ,,mixers ,,etc4 ,,engineering ,,works3 ,,carpenters ,,road1 ,,stratford ,,london1 ,e4 ,telegrams3 8,,filtrum1 ,,london40 ,telephone3 ,,east #cfc ,,the ,,stoddart ,,continuous ,,sewage ,,filter ,,the ,,best ,,for ,,large ,,and ,,small ,,sewage ,,works ,,over #ejj ,,installations ,,at ,,work ,f4 ,wallis ,stoddart1 ,western ,counties ,laboratory1 ,,bristol4 ,telephone3 #ahdc ,,avenue 7#c lines74 ,telegrams3 8,,keesh1 ,,london40 ,,filtering ,,material ,,for ,,sewage ,,beds ,,frank ,,keep #i and #aj ,st4 ,mary-at-,hill1 ,e4,c4 ,,naylors' ,,patent ,,aerating ,,tiles ,illustration3 ,,stock ,,size1 ,,length #ah01 ,,width ,,outside #ab01 ,,width ,,inside #i04 ,,used ,,by ,,over #ej ,,authorities4 ,,several ,,repeat ,,orders4 ,,material--,indestructible ,salt-glazed ,stoneware4 ,,strength--,tested to over #i tons per sq4 yd4 without breaking4 ,,cost--,exceptionally low4 ,,output--#bejj sq4 yds4 per week4 ,,special ,,tiles ,,supplied ,,to ,,suit ,,circular ,,and ,,octagonal ,,beds4 ,,export--,the tiles are easily nested1 and works being near ports1 shipping orders can be especially well executed4 ,,naylor ,,brothers1 ,,denby ,,dale ,,burn ,,brothers' ,,patent ,automatic ,sewage ,disposal ,apparatus ,illustration ,automatic ,alternating and ,timed ,discharge ,syphons applied to ,contact ,filters4 ,extreme simplicity1 absolute accuracy1 entire freedom from choking1 and no moving parts4 ,awarded ,,silver ,,medal by the ,,royal ,,sanitary ,,institute4 ,illustration ,patent ,automatic ,rotary ,sprinkler ,self-clearing ,orifices4 ,requires attention about once a week or less4 ,sewage ,lifts1 ,valves1 ,penstocks1 etc4 ,,rotunda ,,works1 #c ,,blackfriars ,,road1 ,also at ,,edinburgh4 ,,london1 ,s4,e4 ,geo4 ,kent ,ltd4 ,specialists in the measurement of ,,water1 ,,sewage ,,gas are at the disposal of ,,sewage ,,works ,,engineers who desire advice as to the introduction of ,,efficient ,,reliable ,,sewage ,,regulating ,,measuring ,,apparatus ,g4 ,,kent1 ,,ltd41 #aii ,,high ,,holborn1 ,,london4 ,,mechanical ,,sewage ,,screening ,,apparatus 7,automatic7 ,illustration ,,john ,,smith ,,co4 ,telephone3 #ef ,sutton4 ,engineers1 ,,carshalton4 ,,the ,,mansfield ,,patent ,,stoneware ,,aerating ,,tile ,,for ,,floors ,,of ,,bacteria ,,beds ,,and ,,filters ,manufactured by ,h4 ,r4 ,,mansfield ,,church ,,gresley1 ,,burton-,,on-,,trent ,this tile has met with unqualified success owing to its superiority in design over all other tiles4 ,its advantages have been recognized by leading ,engineers1 and it has been largely used throughout the ,kingdom4 ,,hard ,,smooth ,,surface1 ,,preventing ,,fungoid ,,growths4 ,illustration ,,easily ,,and ,,quickly ,,laid ,,without ,,skilled ,,labour4 ,see page #ic in this book4 ,,supplied ,,to ,,the ,,following ,,authorities ,,and ,,schemes3-- ,birmingham ,tame and ,rea ,district ,drainage ,board4 ,metropolitan ,water ,board4 ,corporations of ,lincoln1 ,maidstone1 ,tunbridge ,wells1 c41 c4 ,crieff ,sewerage1 ,tipton1 ,wednesbury1 ,tamworth1 ,chard1 ,whitwick1 ,nuneaton1 ,enfield1 ,chesterfield1 and many others4 ,,descriptive ,,book ,,or ,,sample ,,tiles ,,and ,,prices ,,on ,,application4