TKEAT/nENT OP SEWAGE BY THE A. A. HAMAEK/^AN ARAOUR INSTITUTE OF TECHNOLOGY 19 2 0 628.3 H17 •i- ■<:■ •■ : ' of Tecliaoiogy UNIVERSITY LIBRARIES AT 539 Hammerman, M. A. Collective data on the treatment of sewage by the For Us8 In Ukary Only I ; V U in ( (I U I [IN, /. I, S ( (■ I ' ,' f ' ' ^ Collective Data on the Treatment of Sewag,e by the Activated Sludge Process A THESIS PRESENTED BY Meyer A. Hammerinan TO THE PRESIDENT AND FACULTY OF ARMOUR INSTITUTE OF TECHNOLOGY FOR THE DEGREE OF Bachelor of Science IN CIVIL ENGINEERING May 1920 ILUNOIS INSTITUTE OF TECHNOLO PAUL V. GALVIN LIBRARY 35 WEST 33RD STREET CHICAGO, IL 60616 [jj DEAN OF ENGINEERING STUD DEAN OF CULTURAL STUDIES I. r ( i- TASLE QdP CClTTICvTTS Bibliograplij'" Acknowledgement Introduction Experiments Leadin;^; To Dis- coveiy Early Exijerimenta Experiaasnts At lilancliester Experiments in The United States Llilwalkee ExxDeriments The Sludge And Its Disposal Graphs page I' V 2 n 5 n 9 ft II ti I6 n 22 It 53 ^9113 Digitized by tine Internet Arciiive in 2009 witii funding from CARLI: Consortium of Academic and Researcii Libraries in Illinois http://www.archive.org/details/collectivedataonOOhamm Biblioiiraploi'- Engineering & Contracting Engineering <2c Contracting Enginesrini; ^ Contraotihii En^ineerinji & Contracting Engineering &; Contracting Engineering & Contracting ■3ngin»ering ic Contracting, Eng ine e ring ?Te vvs Engine erihg ITews Engineering Ivews Engineering ITews Engineering ITews Engineering ITev/s "Engineering ITews-HecoSA^ Engineering Record Engineering Record Municipal Journal Oct. P7 1915 Tsc, 1, 19 15 PeiD, 2, 1916 liar. 1916 Ai^r. 26, 1916 xTov . 8, 1916 Jul. 51, 1918 Apr. j^. 19 15 Jul. 15. 19 15 Jul. 29, 19 15 Pec. 2 , 1915 Oct. 12, 19 1 6 17ov- 25. 19 1 6 ITOT , I, 19 17 Apr. 5, 19 15 Oct. ^16, 19 15 Pe"b. 10, 19 1 6 I t^!k« this opportunity of expressing m/ appreciation to Professor John C. Psnn for suggesting tliis sutject and to Miss A. E. Pisher, librarian, whos« assistance in the literary was a jcreat help to me in preparing this thesis. -I- Introduction until recently the medical profession has been the sole guardian of the public's health. The system it uses is to prescribe a cure for a disease, but it does not seek to prevent it. The engineering profession however, lead by the sanitary engineer, is supplanting to a certain extent the doctor and his medicine. A typical case is the fall in the death rate due to ty- phoid fever. This was accoiirplished by sanitary methods of treating drinking v/ater. Other cases involve the disposal or treatment of sewage. The best, cheapest and most efficient method of attaining this end is a matter of much dis- cussion. One method which has been devised re- cently is the treatment by the "Activated Sludge process". The writer has chosen this as his subject, because of its infancy and great future. The day will soon come when every city and town will have a sewage disposal plant that gives a profit and is not a deficit to the operators. -31- Experinients Leading; to Discovery. The method of treating seaage 'o'j the ac- tivated sluge rjrocess was first formulated oy Po'<7ler and iiuciford, who were conducting experiments on sewage in Lianchesterj Eng, , in 1915» They were investigating; the action of an organism which they designated as lij , Thej/ found that, if this or_ anism was cont'.'/i':'ed in sewage, the sevrage was clarified after 6 hours of aeration and that the effluent was non- putrefactive. This sluce -olayed an impor- tant part in the results obtained, as it was noticed that if the sewa^^-e samples were aar..;- bed continuously for 5 weeks, complete nitri- fication '.vas ohtained, Twlien more samples wero^ to he tested, the clarified sewage was drawn off and the nev/ sample w.-..s used .vith the old sludge. The time for oxidation v/as reduced tc 24 hours after a number of samples were clari- fied without removing the sludge, T^nese experiments were "brou'ht about in -S - order to find a cheaijer and raoxe satisfactory method of treating sewafee. It was known that the most costly part of modern sew?.ge works, including the ca,pital expenditure and often the revenue charges, was the filtration area The area and cost of filter beds depends naainly, it was found, on the amount of colloidal matter present in the sewage and much confusion of ideas was due to the fact that the ordinary sewage filter, "be it contact or trickling, Jras called upon to do t'.ro entirely different things aj the same time^for it to oxidise, granulate ar.d finally discharge as humus the colloidal uatters present and second to oiidize and nit- rify substances in true solution. It w-s also rhovm that a tank effluent, well clarified Tpy sedimentation could, by accurate distribution be very efficiently purified on filters of fin^; ;ra,terial, but even then the area and cost in- Ijolved in exceptionally large works, made the problem a verv serious one.' -4- For these and of.-.er Tez.zons the thoughte of niany v.'-orlcers in serrar:e treatment ivere turned to the poEsitility of a more efficient re- i"oval of the collodial matter before the fi3^ tration process. Sefore this process was evolved ^only pr:;x- tical method was oy heavj' chemical precipit:a- tion. The cost cf operating a plant vThere'by the collodial matter was removed "by the addi- tion of a chemical to the sewage was very hi _;.h and was money thrown a^vay. It '^as not only t'xe cost of the enormous quantities of chemdcals necessary, hut the removal of the vast amount, of resultant sludre that "became increasingly difficult and costly. Messrs. Fowler and TJIumford sought to find a method of obtaining a thoroughly clarified efficient -dthout the use of large quantities of chemicals and with the minimum production of sludge. By a thoroughly cl:,rif3ed §-iflmnV: is mea.nt one ':frAcla wi 3 1 not eventually depos- -5- solid matter either on the "oottora of a stream into \f;hich it flows or in the interstices cf a bacterial filter, Mr. Murriford in the coarse of research in another riutter had the occasion to study tlie the action of an organism occuring in nature, in pit '.vater impregnated with iron. This or- ganism-which for convenisnce has 'been desig- nated as W/ is a true facultative organism, preferably an aerobe, and exercises a specific action on iron solutions. It was found that this hacillus precipitated ferric hydroxide from iron solutions and in order to precipitate the iron sufficiently the organism required a cer- tain proportion of alhuminoid orr.anic matter. It was therefore natural that ordinaiy sewage r;hen acted upon "b}'- this organism could he util- ised in this -vaj;. Experiments, in fact, showed that a sewage effluent could be effectively clarified in this u'-ay when acted upon by this .or/;:anism in the presence of si/w 1 Quantities -6- ^, «*>'* of ferric ycilts, a,na tierobic ooriviitions l/eiiie iTiaintained in tlie liquid 'b;'- means of a current of air. The process requires therefore that t'.e grosser solids should be removed Toy sedimenta- tion so ciS to have the least a,mount of putre- factive mt?,terials in the liquid portion of the s 6 rra^c e • The ordinary methods of sewage analyris fails to reveal the change which has really taken t^lace during this process, as they do not differentiate "betv^een organic nitrogen- ous material, in the colloidal and cr^T-stal- lojdal states respectively. -8- r.ai:ly Experiments. Experiments in tlie laboratoiy were iriide v.-itli the conditions during the process maintained as far as possible aerobic throughout, and there being always a certain amount of ferric liydrc.te j::re£ent to oxidize offensive sulfer compounds o.nd no offensive odor v/as produced. By this method a liiiiped sparkling and non~ ,-utrifactive effjuent was obtained from domes- tic sev/age dravvTi from a sewer near the labora- toiy, Experiments indicated that one gram of iron- salt per f-allcn ^as the maximum need and that a total of twelve hours tankage, i.e. six liours aeration and six hours settlement, was sufficient. Another feature found out w-s that once the ; ro'wth of or.r-anisms liad been established in tJie tank, there appeared no difficulty in maintain- ing it. The one hindering feature however, was file cost of air blast; the pressure of air ho'.7- ever, depended eimply on the dejjth of •iV:^ter to -9- Toe Tolown through and a numliex of , _ ' ^-'eerin-- conditions ^vould naturally affect part of 'lis protlem. The advance claimedj is the use of a spe- cific orgciinism found in nature, together with iron salts, to affect the clj^rif icaticn of the effluent, that is, the coagulation of the colloidal nritter as distinct from the .ur- ifi cation of the effluent taken an a whole. To use a simple illustration the addition of . little rennet does not appreciahHy alter t^ie contents of milk as a whole, "but separates it into a solid and liquid portion. The endeavor of tlie discoverers was to obtain a similar re- sult in the case of seva-e tank effluent. -10- Experiments at Llanchester. Purther experdnients were carried out on this line "by Messrs. Arden cz Lockett in 1914- at jvlancli ester. Tlie sanTnles consisted of 80 oz, cottles of I'ilanchester raw sewage. They were a.^r- -vted until complete nitrification, h\'' dra^;ing _,ir through the sewage "by means of an orddnar;/ filter pump. For the first sample five weeks -:s required for com";lete nitricication, after •" '.ch t]'ie clear liquid was dravv-n off and another s:;. ^le of 80 oz. added to the bottle containing the set- tled sludge and this again aerated until complete nitrification. This method of treatment vras re- peated severa] times .vith retention in each c,:.i-ie of the deriosited solids. It w-s found that the amount of solids in- creased and the time required for each success- ive aerating- deminished until it ivas possihle to oxidize a fresh sample within twenty- four :ars. The experimenters ca.] led these deposited r^clids ""ictivatea sj-uogei* -II- \^ith tliisc activated siud;"e a further se- ries of samples '^ere tested. In general a pro- vortion of one Tolurne of activated sludge to four volumes of s enrage of tiie ■jreceeding ex- periment much smaller proportions were used. rrom these tests the following.- conclu3i(r;i3 ■vere ms.de, tha-t an extraordinary high degree of x->urif ication can "os obtained ;vithin a rei'- sonahle period of time by aeration in contact '.vith the activated sludge. The amount of ni-. trificition dependih;^; to a certain extent on the concentration or strength of the sewage dealt with. On the averajje, aeration under tlte conditions of the experiment for a period of ix hours, with subsequent settlement, was suf- -"icient to obtain a high percenta£;e of pmri- fication. In all cases the resultant effluent "as non-putrefactive on incubation. . These experiments were 'vorked on the dra- md fill method and. it 'vas anticipated that equally f-ood results could be obtained by vvor^li- in.^ on a continuous flow basis. -12- Further experiments in tiiis line showed that the activity of the sludge is gradually diminished, when working on the fill and draw method, if it is called upon to treat futher samples of crude sewage, prior to the complete nitrification of the previous samples dealt with. The results also showed that this difficulty would be overcome by simple aeration of the sludge alone, until the free or saline ammonia content was removed. Experiments were then carried on to deter- mine the influence of temperature on the oxida- tion, prom these experiments it was found that the oxidation process could be maintained with- in a fairly wide range of temperature. The ex- periments carried on for temperature less than 10 C showed that an inactive sludge was produced. With a temperature of 30°C it was found that the initial clarification effect was to some extent interfered with and that the effluent resulting from subsequent settlement showed a slight deter- ioration, , -13- Activated sludge aocumulated in this raadAer as descri'bed 'oy the investisators is "quite inoffensive, dark Taown in color, and flocculent in character, and despite its low specific grav- ity separates from v;ater or sewage at a rapid rate. After prolonged settlement the activated sludge, however, rarely contains less than 95 per cent, of water, A remarkahle separation of the water from the sludge can he readily obtain- ed "by treatment of find grade strainers, with the production of a sludge of the consistancy of a stiff jelly. Gelatine counts have shown a bacterial content of at least thirty million or- ganisms per cubic centimeter. In addition, the sludge, hy reason of its nitrifying power, must of necessity contain a large numher of nit±lfy- ing organisms. It should also "be noted that a fairly large nura"ber of protozoa were found". It does not, however, contain any algae growths. The chemical analysis of an average sample of activated sludge is as follows :- -14- Organic Katter 64.7 Per cent Mineral " 35.3 " " Total nitrogen (n) 4.6 " " Phosphate (PS 05) 2.6 " « Matter extracted "by CarlDon Tetrachloid CGL4 5.8 " " Attention should 'be called to the ahnorcially high percentage of nitrogen as compared with ordinary unoxidised sewage sludge. Experiments 77ere carried out in the open, as compared v;ith the previous experiments which \7ere performed in a laboratory and the same results ob- tained. An air diffuser was also uded instead of an air tube and the results showed and increase in the oxidation of sewage. A continuous system of flow was also tried and the result was that the amount of ammonia present in the effluent increase'd as the experiment proceeded and rendered it necessa- ry to recirculate the effluent through the aera- tion tank again. Prom this it was seen that the sewage must flow very slowly through nine series of aeration tanks in order to properly purify -15- the sewage, -■■ ■ ! I Experiments in U.S. Similar experiments of this sort were con- ducted in America at Urbana, 111, in TsToTrem'ber 1914 and then tn a large scale in May 1915 by Edward Bartow and 5',W,Mohlman of the State Y/ater Survey, University of Illinois, The first exper- iments were made on raw sewage without activated sludge present and the results showed that com- plete nitrification could be obtained within the limits of 15to33 days by blowing air into the sam- ple by way of a tube. They then used an air diffu- ser with a similar sample of sewage and complete nitrification accured within 15 days. In each case the faee ammonia nitrogen was oxidized to nitrite nitrogen and further oxidised to nitrate nitrogen. It took 4830 cuft of air in the second case for the forsiation of the nitrate. At the end of seven days the free ammonia nitrogen was com- pletely changed to nitrite ni tro gen , slowly changed to nitrate nitrogen. -16- When a similar sample was examined in the presence of activated sludge complet nitrifica- tion "was accomplished in five days and the amoimt of air used "was only 1270 cu. ft. The supernatant liquid was then drawn off and another sample added to this accumulated sludge and aeration continued. In this treatment complete nitrification took place in two days with the use of hut 720 cu.ft. of air. Treatments 7;ere continued, al-ways de- canting off the clear liquid and a new sample added to the sludge accumulated until the twelfth treatment, when theresults shov?ed complete nitri- fication in less than eight hours with the use of only 128 cu. ft. In the thirty-first treatment there had already settled enough sludge that the proportion of sewage to sludge was five parts to one part. Por this sample purification was oh- tained in less than five hours using 35 cu, ft, of air, this heing ahout 3 cu.ft, per gallon of sewage, samples taken every hour of the sewage, in the operation of the last experiment named, showed -17- ■) -;j/ M :. n 1 I , \ rr\-c I I I \ At Uji i _ that the free ammonia is not chagged to nitrite and the nitrite oxidised to nitrate but that ni- trates and nitrites were formed simultaneously. Biological examinations then made in the sludge showed the presence of a slender v/orm whose lenght varied from two to five ram. It is known to abound in fresh water bodies where there is an abundance of decaying organic matter and thrtves especially where there is much fermen- tation and in waters contaminated with sewage providing there is an abundance of oxygen. These worms probably destroy at least their own weight of organic matter each day. Because of their re- production by fission extensive colonies can be produced within a short period. These worms, no doubtedly are the main con- tent of activated sludge. The sludge does not have an unpleasing odor, owing to the fact that it consists largely of living organisms. If kept for a long time in a moist condition without air i t will piitfcfy. The chemical analysis of this sludge after drying first on a water bath, then for three hours in an oven at lOO^C the loss of -18- t^ moisture Tseing 95,54 j\er cent» was:- lTitrogen(N) 6,3 Per cent, phosphorous (p I 1,44 " " phosphate(^P^05) 3.31 ", " Pat 4,00 " " Volatile matter lost by ignition 75.00 " " The percentage of nitrogen and Phosphate are higher in this sludge than that obtained at Manchester, Eurther experiments v;ere made at Urbana in May 1915, These experiments "were conducted in four large concrete tanl:s each having an aeea of 10 sq.ft. and 8ft. 5in. depth above X^ in. filtros plates which were used to dif- £use the air. In two tanks, hine plates were used with spaces of one inch betv;een them and in the third tank there were three plates cov- ering one- third the area of the floor with a central tl'ough sloping to the plates at an an- gle of 450, Jn tiij fourth tank one plate was used in the center covering one ninth the area of the -19- floor and 7a th the bottom sloping to it at an angle of 45° on all sides. Below the plates was an air space of four inches deep. These tanls could "be filled in six minutes and drained in eight minutes, through two outlets which are re- spectively 2» 6" and 5' 7" alROVe the porous plates. Uo iludge was lost through the outlets of the third tank "because movable outlets were used. TJie first and second tanks were filled with the same kind of sewage, the sewage in the first tank be- ing aerated continuously, and in the second tank for 23 hours, the sludge b44ng allowed to settle and the supernatant liquid drawn off and one hour later more sewage added to the collected sludge. This cycle was repeated daily and results were recorded. After ten days one per cent of volume in the first tank was sludge and in the second tank 10^, The effluent from the second tank was clearer than that of the first tank. The opera- tion of the second tank was continued as before and after 15 days, nitrification was complete. -20- The sewage was then changed every twelve hours and nitrification was complete in eight days. Changing the sev.'age every six hours did not show good results and it "was necessary to aerate for longer periods. This comparison indicates, how- ever, that sludge may be satisfactorily activa- ted by changing the sev.'age before nitrification is completed and that the sewage may be changed at frequent intervals. The third tank give stable effluents after five days. The fourth tank did not give stable effluents in 18 days*^ Further experiments at Jlrbana with activated sludge took place in 1916 with continuous opera- tion and results showed that 90^ of the suspended- matter was removed and after 13 days of operation stable effluents were obtained. -21- MilwauJ^ee Experiments, Further experiments v-ere carried out "by T. Challcley Hatton* chifif Engineer, llilwaukee Sewage Commission at Milwaukee since 1914, The magnitude of these experiments Taeing larger than those at Urbana, Experiments were carried out in liTarch 1914 one a small scale so as to get an idea as to the plant necessary to experiment on a larger scale, Tww glass tubes 6' long "by 1^^' in diameter were used. Air was forced into one of these tubes through filtros plates and an- other through a tube. Results showed that after 24 hours aeration in each tube the nitrification in each of the tubes was about the same, A tank of Isrger capacity was then built outside. This tank measured 32 ♦ lone 108 6" wide and 10 » deep, piltros plates were set at the bottom of this tank and the effluent drawn off by means of a floating circular weir. This tank was operated under varying conditions. The results for nor- mal conditions being, filling one hour, aerat- ing three and one-half hours, settling one-half and drav/ing one hour, Further experiments were carried on in a tank 10 ft. hi^ 5 ft wide, one foot between sides. Glass plates were inserted at various depths to observe the action inside. The results obtained from -/this experimental tank showed a greater number of bacteria per c .c, for the filteos tank than for the iit . ■ Jet diffuser tank.Sxperiments were then conducted on continu- ous flow operation. The tank being of the same size as the one used in the second set of exper- iments. This tank was put into oeration after securing the activated sludge. Experiments were carried out with varying Trolumes of air per gal- lon of sewage treated, varying rate of flow and varying the volume of activated sludge. The re- sults for this tank are as follows, the larger percentage of the sludge in the tank, the more nearly complete nitrification is obtained, that is, for percentages of sludge up to 12-g^ for vol- ume. All of the preceeding esflperiments were car- -23- %'.'.^' ried out in relatively warm weather, so the question came up as to hov; the process .vould work in cold weather, as the "bacteria did their test work in tezaperatures between 689 to 70°P Tests were made on the liilwauicee Sewage in Win- ter the temperature of the Sewage ranging from 55°p to 420p and it occasionally dropped down to 4oO These ?ery low temperature, re tar ted the oxidation of the organic matter and decreased the staTaility of the treated liquid. Activitjfng this sewage with 2^ cu, ft. of air per gallon, 90 per cent of bacteria in the se;vage was removed and the suspended matter reduced to about 15 parts per million. By increasing the ipolume of air applied ■ the plants could remove the suspended and col- loidal matter and bacteria in a satisfactory manner. As the temperature of the sewage dropped the oxidation of the organic matter decreased the nitrates in the effluent falling more than 100 per cent for a difference of temperatures -24- of 63*^ to 49° 3-^^ the oxygen consumed "was in- creased 75^. Tlie decrease in oxidation was al- so accompanied ^by a decrease in the stability of the effluent. In cold weather the treated liquid contained a large percentage of dissol- ved o:xygen and only a trace of nitrate, where- as in suminer the nitrates were high and the dis- solved o:jcygen low. This shows that the liquid seems to depend upon nitrates in summer and dissolved oxygen in winter for its stability. This shows that in winter temperature, good "bacterial removal and ci.arification can "be aiaintained without oxidising the ammonical nitrogen to nitrate. These, and the proceeding Kil*aukee exper- iments proved that it was possible to treat the sewage of Milwaukee by the activated sludge pro- cess on the continuous flow method when the tem^ perature of the sewage was 50°P or over at less cost than by any other process. It was then de- cided to build a plant having a capacity of 1,600,000 gallons a day. The estimated cost of -25- the plant was ^65,000 "but the plant -was complete^ in January 1916 at a total cost of but $61,536 in- cluding all machinery and cost of engineering and inspecting. The activated sludge plant is Ideated on Jones Island, alongside a large outfall sewer of the com- bined system. It consists of eleven cylindrical, so that if the activated sludge process should fail they could be easily converted into Iichoff tanks. Of the elven tanks, eight used in series are used for aeration of the selvage in the presence of ac- tivated sludge, one is a sedimentation tank and two are sludge, aecation tanks. The sise of the tanks are as follows, they are all 30* in diameter and have side walls extending 13 ♦ above its inner bot- tom. The total depth of sewage and sludge is 10* and the average depth is 9' in the ten tanks used for aeration. The sewage and the sludge in the sed- imentation tank is 35, 2» deep. The holding capacity of Aach of the eight sewage aeration tanks is 45000 gallons or 360,000 for the group. The open area of -26- © ,■ 6ach of these tanks is 662,84 sq, Pt, and all 4f them 5,303 sq. ft. The sedimentation tank has a holding capacity of 33, 000 gallons, not including 2,260 gallons held Toy the 48" cast iron sludge pipe extending "below its bot- tom. The general scheme of operation is as follo"ws: the sewage is admitted to tank 1 where it is aerated with activated sludge, it then passes succession through the first eight tanks the combined sewage and sludge passing on from one tank to another and then into the sedimentation tank 9. Here the sludge settlement and the clear liquid passes out in- to the lake, Prom the bottom of the deep well in tank 9 the sludge is discharged by gravity into either of the sludge aeration tanks 10 or 11, The aerated sludge from these tv.'o tanks passes outside the tanks to a 48" vertical cast iron pipe set 28^« in the ground from which it is lifted by air and returned to the inlet to the sewage-aeration tank 1, -27- Tlie portion of the activated sludge in ex- cess of what is necessary to maintain the proper percentage in the aerating tanlca. is pumped out of the sludge tanks from time to time and de- watered and sold as fertiliser. The normal lake level is at El, -1.4. Tlie sevjage level in tank 1 is El,-V 0.8 and the weir in the sedimentation tank is at El. ^ 0.5 giving a fall of 3» in water level through the series of tanks. By means of the curved baffle or division wall: the sewage travels and is subjected to aeration for a distance of 912». Air diffusion affected "by means of 12 x 12 in. filtros plates 781n each sewage and sludge aeration tank. This gives a ratio of diffusing surface to tank sur- face of 1 to 8.5. Tlie filtros plates are set in aast iron frames, which afford an air supply con- duit beneath the center line of each plate . The estimated air capacity of the filtros plates in the eight sewage aerating tanks is 2 cu. ft. per minute and in the tv.'o sludge aeracing tanKs it is -28- 12 cu.it. in ecion c^se unaer u, 2 in. ^c^ter pyeseure. This plant was designed to treat 1, 600,(X)0 gallons of sevrsige per djy with a four hours es.. iod of aeration and with 25 pe^: cent activated sludge content, a velocity of 3.8 ' per min. and 27 min. sedimentation petiod. It can also Toe run with 25 P^i" cent activated sludge pres- ent running through at a velocity of 5 ^"t* "02: 5 hours and a 20 Eiin. sedimentation period, the capacity for this operation "being 2,160,000 gal- lons, A capacity of 2,304,000 gallons daily is ohtained .vith 20fS activated sludge running through at a velocity of 5 ^t. per min. for 3 hours and a $SL 19 minute sedimentation period. The results drawn from this plant after a year of continuous operation are numerous, and man;,'- new experiments were tried there, but on a larger scale, and their results obtained. mien this plant was first put into operal^i^n it required from 30 to 55 claj'-s of aeration to o"btain a sufficient cuantity of activated slud^ -29- 30 as to start work, and in order to niaintain 25 per cent of activated slud£:e in the aerating tanks it had "been found necessary to return frora the sedimentation tank from 40 to ^0 per cent of the voluire of raw liquor treated, hecajjaea the Li- quor drav.Ti from the sedimentation tank was only about one-half sludge. Tests for this best diffusers to use v;ere also made. It was found that the filtros diffu- sers created too much frictional Iobs, the loss being three- fourths'^f or forcing a five'^-air pres- sure through. Tests v/ere made with wood block cut from basswbod across the grain and the fric- tional loss for these filters were only oneOhalf pound for five pound air pressure. The wood fil- tros plates are cheaper and nitrification V7ith less air could be secured by increasing the dif- fuser area about 3^fo over air required for fil- tros, and thus reducing the volume of air pas«- ing through each square foot of diffuser. The aerating tank which gave the best re- -30- suits in luilwaukee has the following proportions: 1 sq. ft. of diffusing surface to 5-5 sq. ft. of' tank surface, average depth of liquor, 9 ^t. 275 gallons of rav; sewage treated per day per sq, ft. of surface. One culDic foot of aerating tank ca- pacity treats 29 gallons of sewage per day. The results obtained from the sedimentation tank at this plant were not very good, the Elua,:e could not lina its wd^'- dov/n the central well and therefore collected on the sloping iDottom of the tank and the sludge became septic. This settling in this manner v;as due to an entrance velocity which -^.s too great and adverse currents were established which held the finer flock in sus- pension, permitting it to pass over the wtn with the effluent; the heavier sludge v/ould settle or the sloping bottom and not slide down to the central well and it became septic there, Prom further experiments conducted it was found that the tank giving the best Sedimentation was a tank ,7110 se ratio of -^he breath to the len^JtCti -31- m^ lii^'i'w was as 1 to 2.3 with flow across the breath. The running velocity should not exceed 3 ft. horizontal per minute. The detention period may Toe i'rom 30 to ^0 minutes, according to the character of the selvage treated. Vertical- horizontal flow heing more efficient than either vertical or horizontal flow. The eff3.u- ent should he removed with the least Velocity Tjossihle and over Continuous rather than V shaped weirs the latter creating cross cur- rent just where they are most ohjecitional. -32- Tlie Sludge and Its Disposal.' After ti'id sludge ccllects into the sedi- /iientation tank it is rei.-oved, aevntatered, pre-Soed .-nd sold ae fertiliser. The fertilizer "being ^,old for ^12.50 per dry ton in 1937, Tlie cost liowever, of pressing and di^'^ing; the sludge v.-_. ich Included inter^r^.t charges and plant deprecii-.tion, lalDor and iraterials vvas ahout. $8.75 per dry ton. The clear profit bein ^5.75 per ton. An analysis of the sludge ohtj^ined is as follows: Nitrogen ^.lf= as 1^5 rat 5.3^ « Soluble Phos- phor i c ac i d 9 . 5/'V Potash ,2^'ji The value of the sludge depends upon sev- eral things among v.-hi oh may be v/entioned the percentage of availa'ole nitrogen and the quan- tity of fatly liiatter it contains. The nT-;htr the nitrogen content, the more vailuaV.le is the sludge for nianure, but on the otlaer hand, the hi^^her the fatly content the less &uitc*Gxpi is -33- J- " ti'ie oiuci^e lor agricultural use until the i.^.t- Ler inateria,! has "been reixoved. Ho'vvever, the rore f-ot present, tlie more advisable it is to i-i-eat the £lud:.e to recover this fat, if it is _. resent in consiaera'ble quantities, ■Estirnating that one dr;" ton could he o"b- tained from 1,000,000 gallons of sewage treat- r-d. and an average daily dry v;eather flow of '5><^00,000 gallons the nc-t cost of disposing >!il',vaukee ' s sewage r/as estiinated at |9.64 per 1,000,000 j^allons of which 4-. 39 is charged to overheads and ■;4-.75 "^'^ operating, uenewals, and repairs. The net cost of operation per capita is figured out to Ids ,53p» But this Tfidy not Toe true, The actual valu-^ of sludge manure, depends upon the ease with '.■/hich it can "be disposed of. Por small coiiunu- •-ities surrounded hy rural districts fiere may 'ossilDly no trouTole -.vhatever of disposing of this sludge at a payahlo ^.rice. !But v;hen a, rrr-i.-.t osnter is considered, where great quantities of -34- < ( the sludge could "be xDroduCv...^, .^.,^/c is more t.-.an can "be used by tlie surrounding farmers^! to ■; et rid of it, uovld have to "be transported a £r;^at distance and sold at :z cheapear price to make up for 're transportation cost. Sewage sludg-c, ho-.vO 3rer .' high in available nitrogien is not BBch a rich manure that it can stand the cost of hein^ carried half way across t'le \7orld like the chil~ ean nitrates. A comparatively small amount of handling and carria^-e kills it as an article of commerce. Activated sludf;:e can he stored for a time oeca-use there is no offensive oder to activated sludge, but considerahle oiier mxay attend impioper siudge reduction. Partially de'.vatered sludge, if exposed to the sun for a few hours gives off a . ighly oh.iectional odor of hydrogen sulfate. This odor lasts for a short time only or until a .Iiy cohering is formed. Suldge placed under cover and not exposed to the sun ::^.ives off little or no odor. Flies, insects s,nd '.vorms do not infest the -S5- - ©r:*fW^, treatment plant, even during tlie early fall vhcn tiiey are so prevalent in nearly all otl.sr types of disposal plants. -36- a ! - ' ■' i • i p-- .,,... !■ ; i ' '■■■- r ■ i 1 1 Bacteria DuriNa i Different Periodsiofl i i : - i— - . 1 L-.- ,■_._. .J L^Aeration f T I \ 1 i- - - 1 1 j : ( ! / / / t^i *^ -_ - CODE' 9 per ceJotAc+ivatei^ludgs Totat Bacteria per c c— Hours Aeration Effect; ot Varyinc^ Proportion'o ofAdivated 5ludge CODE Curves^'-A- lVdl.'51we(ge +o SVol. Sewage - j|--EnJ Veil. Sludge to 6 VoV. Sewage -C- \V<^[.'b\udqe]-o 4 Vol. Sewage 'on , c_ J Vil^Sludaelo 3,Vol. Sewage J Q ^hrgj. Oxygen Ab&brbiion I , I i7 - — .— 'Ereifi.-fiL.Saii'ae M Hj Analtjsi&- ot Sam pie I F|ar+€, per Ml lli'on 5h"<£Wen' 5eH\ed sao 46.S \ "■ Si \ 1 ^ J .!.■.' t '^ 1 - 1 --;"-- t_ I ■ "-'^ U< 1 ■-U ^ j p^- " L^ . -^ i^\ u* :t>'" _^ ^ 1 \ ^— ^ — ^"^ -^ r*- — ■ — j^-^—^ t) — ' 1 . j 1 1 . ^ k^zr-, r — h— -^ •1 tiours Aeration SSiBIGb B :.fferi cff Varuina ! " T 1 .; ' " ""' i . |. _- - 1 - 1 - J i-'n-l^^ v| \ "it !'* !_:'/:l -{ i ' i [ -— M-rtT-'-^ ! ■ ■■ I ■ ! __ j__ i i 1 ■"■■■■ 1 ■ i 1 — 1 , - _ t-M ^ _ ti+7---"-| . L-^-i ..." ^--T^-j rn;vi .L3i 1 ^ .1" .1- i. -1 'i^'T, ^ri^-:'i -i-f ■ ^tIh? ft;v- i 1 QiL>E. - i_--j ,-■ - ' '-■'^ f ' ;_■_, <1MfTrt'0 nia _ I: - ; ^i-lL:,.- ssacTfff rer.n^ TmHIHH '. — ^^ t - - '■*-- '^i Vi - J lEij. i-kii+K' j.-i-Llar.'-.' :;:ii~' -''±-: , rjiiTr age a&i nn 1 !"-^ ~7~*r -J p. -J- Se i.ti ■.- 1 T^ J .- 1 ., ^■ 1 . ^ .75 cu;i|t pif : ti ^"^ ^ " ^^: per gal joL Stewafl 1 1 ^ i L - -. , x' -, —A y" <. 1 <■'■■". ! ■" ■• 'T!:^^ I r J ^ L-^-. - - >-' — ._. ..J Hours Aeratioo