T H E J O U R N A L O F I N D U S T R I A L ,4iTD E N G I N E E R I N G C H E M I S T R Y
318
PURIFICATION OF SEWAGE BY AERATION I N THE PRESENCE O F ACTIVATED SLUDGE By
EDWARD BARTOW A N D F. W. MOHLMAN Received March 12, 1915
I n a paper1 read before the 'illinois Section of t h e American Water T o r k s Association, Yovember I I , 1914.it was stated t h a t experiments in the purification of sewage b y aeration in the presence of activated sludge were t o be carried on in t h e laboratory of t h e Illinois State V a t e r Survey a t t h e University of Illinois. With the advice of Professor G. J. Fowler of t h e University of Manchester, t h e experiments are following t h e lines described b y Ardern and Lockett.* While we have tried t o avoid a repetition of the work of Ardern and Locltett, we have found i t necessary t o repeat some of t h e experiments described b y them in order t o familiarize ourselves with t h e process, t o obtain the necessary activated sludge and t o study t h e reactions involved. We are studying the necessary mechanical devices, the physical, chemical and biological conditions of the process a n d the properties of the sludge. Since Ardern and Lockett have abandoned, for t h e present, experiments with continuous flow devices, we also are confining our experiments t o an intermittent system. O u r first experiments were made using bottles of three gallons capacity. Later, we constructed a t,ank g inches square and j feet deep. This t a n k has plate glass front and back t o permit easy observance of t h e condition of t h e sewage a n d sludge. 4 porous plate \--as placed 4 inches above
Val. 7,
NO.4
is measured through a n ordinary gas meter. T h e purified senxge is removed b y means of a siphon. Experiments have been carried o u t in t h e laboratory a t room temperature, t h u s far, m-ith no special prccautions t o regulate t h e temperature. For our experiments. sewage from t h e city of Champaign is used. It is collected from a point in t h e main
I
I
FIG.11-iXITRIFICATION
OF S E W A G E .
S O ACTIVATED
SLUDGEPRESENT
U N I F O R M D I S T R I B C T I O N O F . k R T H R O C G H P O R O U S PLATF:
sewer a t t h e edge of t h e city, a t least two niiles from the outfall. V h e n taken it is fresh. Average analyses indicate t h a t i t is a fairly strong, domestic sewage. I t contains no trade wastes. .%ERATION O P
RAW
SEIVAGE
WITHOUT TfiE
ADDITION
OE SLUDGE
7TM.E /N
FIG.I-NITRIFICATION
a
OF S E N A G E .
NO ACTIVATED SLUDGE P R E S E N T
t h e bottom. An inlet for air a n d an outlet for a n y water which might pass through the plate were provided in the space below the plate. Compressed air furnished by the University power plant is used. &\llair 1 "Observations of Some European Water Purification Plants a n d Sewage Disposal Works," Jouu. A . W . W . A , , March, 1915. 2 J . SOC. Chem. I n d , 33, 523-39, 1122-4.
Xir has been blown into five separate portions of sewage until complete nitrification was accoinplishecl. T o show t h e progress of t h e reaction, tests for free ammonia, nitrites and nitrates were made a t intervals during each treatment. The time required for complete nitrification has varied from 1 5 t o 3 3 days. T h e best result was obtained in t h e tank, where the air was distributed through t h e porous plate. For all analyses, samples of t h e supernatant liquid were taken after one hour settling without filtration. In. each case, t h e f r e e a m m o n i a nitrogen was almost quantitatively changed t o n i t r i t e nitrogen, then t h e n i t r i t e nitro,gen in t u r n was changed almost yuantitatively t o ?Litrate nitrogen. This change is illustrated in Table I , A and B and Figs. I and TI. The formation of nitrate in t h e t a n k was accomplished in I j days with the use of 4830 cu. ft. of air. ASKATIOPI- OF RAIV SETTVAGE.TTITH S L U D G E
T h e supernatant liquid was siphoned off and a fresh portion of sewage added t o the sludge. I n this, t h e second treatment, the effect of a small amount of sludge is very nicely illustrated b y t h e reduction of t h e time required for complete nitrification from I j t o 4 days, and t h e reduction in the amount of air used from 4830
Xpr., 1915
T H E J O U R i V A L O F I I V D r S T R I A L AND E N G I N E E R I N G C H E M I S T R Y
t o 1 2 7 0 cu. f t . : 34 parts per million of free ammonia nitrogen in t h e raw sewage produced 23.8 parts per million of nitrate nitrogen i n t h e supernatant liquid. TABLEI-NITRIFICATIONOF SEWAGE: WITHAND WITHOUT SLUDGE PARTSPER MILLION Time NITROGEN AS Days Free NHI Alb. NHs Nitrites Nitrates Date A-No ACTIVATED SLUDGEPRESENT 38.00 5.20 0.07 0.37 Dec. 18, 1914 0
..............
19 21 28 . . . . . . . . . . . . . . . . . . . 29. 30 31
.................. ................... ...................
3 10 11 12 13
30.00 28.80 22.00 8.80 1.60 0.36 0.16
4.20 4.00 3.60 2.60 2.40 1.88 1.48
6................... 7. .................. 8 9
19 20 21 22
0.28 0.44 0.28 0.24
1.92 1.84 1.68 1.60
..
..
B-No
1
0.02 0.11 5.00 16.00 23.00 28.00 31.00 33.00 33.00 30.00 27.00 14.00 .30 .05
0.38 0.45 0.20 0.40 1.00 2.00 1.00
5.00 18.00 31.70 31.95
ION O F ACTIVATED SLUDGE P R IWENT: UNIFORM DISTRIBUTI AIR THROUGH POROUS PLATE
0.71 0.01 0.60 3.40 1.20 32.00 2.00 3.00 2.60 7.50 18.50 19... 15 2.20 0.10 25.90 C-ACTIVATEDSLUDGEPRESENT(1 SLUDGE:5 SEWAGE):UNIFORM AIR 3fi.00 . . . . . . . . 6.fin .
34.00 0.40 0.60 0.80
................
DISTRIBUTION Free NH3
Hours
Feb. 24, 1915
...............
0 1 2 1 4
5
27.00 13.00 8.20 3 70 .... 0.20 0.20
0.05 0.59 2.40 6.00 2.80 10.80 3 . .41) . . . . . 15.00 .. 18.60 2.60 0.30 22.10
The supernatant liquid was again siphoned off, fresh sewage added a n d aeration continued. I n this, t h e third treatment, nitrification was complete i n two days a n d b u t 7 2 0 cu. ft. of air were used: 3 3 parts per million of free ammonia nitrogen produced 2 2 . 3 of nitrate nitrogen. In t h e twelfth treatment t h e purification was completed in less t h a n 8 hours with t h e use of less t h a n 1 2 8 cu. f t . of air and 36 parts per million as free ammonia nitrogen produced 2 9 . 5 parts per million of nitrate nitrogen. I n t h e thirty-first treatment with sludge a n d sewage in t h e proportion of I : 5 , purification was complete in less t h a n 5 hours: 3 j cu. f t . of air were used, equal t o 0 . 2 0 cu. ft. per sq. f t . of surface area per minute, or about 3 cu. f t . per gallon of sewage. We have not yet attempted t o determine t h e minimum amount of air required. Samples taken a t t h e end of each hour of aeration during some of t h e treatments have been tested for stability. A sample taken a t t h e end of one hour aeration i n t h e thirty-first treatment had not decolorized methylene blue a t t h e end of twelve days. Since in one hour nitrification was not complete, it is, therefore, evidently unnecessary t o obtain complete nitrification in order t o obtain a stable effluent. Since i t is impossible t o separate the oxidized liquid entirely from t h e sludge it is probable t h a t t h e stability is promoted b y t h e oxidizing action of t h e nitrate in t h e residual liquid. The progress of nitrification in t h e presence of activated sludge is apparent. The results are shown in Table I I I C a n d Fig. 111. From this a n d from other series of analyses it is indicated t h a t there is no quantitative conversion of free ammonia t o nitrite, followed by oxidation t o nitrate. b u t t h a t nitrates are formed simultaneously with nitrites. T h e number of bacteria were determined during one treatment. Samples were taken after one hour settling.
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The raw sewage showed a bacteriological content of 750,000 per cc. The supernatant liquid after aeration a n d settling one hour showed b u t 20,000. Further tests are planned. These we expect will include t h e determination of species. Through t h e courtesy of Professor Frank Smith, Professor of Systematic Zoology of t h e University of Illinois, biological examinations have been made of t h e sludge. Among t h e microscopic animals found are many Vorticella a n d Rotifera, b u t t h e predominant organism is an annelid worm, known as Aeolosoma hempichi. This organism is about 2 t o 5 mm. long a n d quite slender. It abounds in various kinds of freshwater bodies where there is an abundance of decaying organic material, a n d thrives especially well where there is much fermentation a n d i n waters contaminated with sewage, provided there is a n abundance of oxygen. It belongs t o a group of worms i n which reproduction occurs very rapidly b y asexual methods. A fission zone is formed near t h e middle of t h e body of t h e parent worm a n d develops t h e head of one daughter y o r m a n d t h e tail of t h e other, a n d t h u s two =CY
1
??IO.
111-NITRIFICATIONOF SEWAGE. ACTIVATED SLUDGE PRESENT. 1 SLUDGE:5 SEWAGE.
new worms are formed from one. This requires not over two or three days and is repeated for a n indefinite number of generations. It feeds greedily a n d almost continuously on a n y small organic particles t h a t i t cag obtain a n d presumably destroys a t least i t s own weight of organic matter every d a y a n d probably more. Because of t h e mode of reproduction, it takes b u t a short time t o produce extensive colonies with great capacity for t h e destruction of organic material. SLUDGE-The activated sludge has evidently been developed bfr t h e multiplication of these worms originally present in t h e sewage, and t h e species found a t varying points might differ. The sludge does not have an unpleasant odor, due t o t h e fact t h a t it consists largely of living organisms. If kept for a long time in a moist condition without air, i t will putrefy. COMPOSITION O F SLUDGE-Analyses of t h e sludge made b y Hatfield have shown t h e following results: After drying first on t h e water b a t h and t h e n for three hours in a n oven a t 100' t h e loss, or moisture, was 95.54 per cent. T h e dried material contained 6.3
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Vol. 7, No. 4
per cent nitrogen, 4.0 per cent fat, 1.44per cent phos) 7 5 per phorus (equivalent t o 3.31 per cent P z O ~ and cent volatile matter by loss on ignition. From this chemical d a t a the dried sludge would evidently have value as a fertilizer. If we calculate t h e value as 20 cents per lb. of nitrogen and 1 2 cents per lb. of phosphorus, i t would have a market value of $29.00 per ton. In order t o determine whether the theoretical value would correspond t o the actual value, pot cultures have been started. Portions of dried sludge were added t o two pots, a n equivalent amount of nitrogen from dried blood t o a third, and nothing t o a fourth. &4tthe end of 18 days the cultures containing the dried sludge show better growths than the culture containing an equivalent amount of nitrogen from dried blood and far better growth t h a n the culture t o which no additional nitrogen was added. A plant t o operate on a larger scale is under construction and t h e authors propose t o continue the experiments.
ing the total amount of moisture t h a t is obtained by HzS04 drying; some have the opinion t h a t they get all b u t two- or three-hundredths of one per cent in most cases, while others think t h a t they obtain very much less t h a n t h a t percentage of moisture. At best, any drying method with can be only a n arbitrary one. Since this is an old subject. most of t h e experimental work for this paper is given in abstract, Many experiments have shown t h a t from certain substances all of t h e moisture cannot be obtained by t h e ordinary HzS04 drying method a t 2 5 ’ C. A sample of pure sugar syrup, for example, containing 4 9 . 8 9 per cent moisture, mixed with ten times its weight of sand, yields a n average of about 48.17 per cent moisture. With maple syrup, even with vacuum, t h e same condition is observed. The percentage of moisl ure obtained by HzS04 drying is less t h a n t h a t obtained by t h e refractive index or by heating a t 100’ C. This behavior of sugar, although somewhat exaggerated, STATE WATER SURVEY, UNIVERSITY OF ILLIXOIS is typical of t h e behavior of other substances. The URBANA water-vapor pressure of some materials still containA COMPARISON OF THE RELATIVE DRYING POWERS ing residual moisture is as low as t h a t of the H a S 0 4 over which they have been dried. It has been shown OF SULFURIC ACID, CALCIUM CHLORIDE AND t h a t considerable amounts of H2S04 distil off in vacuum, ALUMINUM TRIOXIDE WHEN USED IN ORDIand for this reason Gore’ suggests the use of CaO for NARY SCHEIBLER DESICCATING JARS’ high vacuums. By graphic interpolation, concenB y J. W. MARDENAND VANNAELLIOTT trated (95%) HzS04 has a vapor pressure of about Received January 28, 1915 In spite of the many objections p u t forward t o CaClz 0 . 0 3 rnm. a t z s 0 C . According t o Thorpe2 the speed of drying is hastand H2S04 for ordinary desiccating purposes, these substances are still quite generally used. Kearly ened b u t no more moisture is obtained by the use every analyst knows from experience t h a t if a per- of vacuum. I n a series of trials with cheese, syrup, and CaC12, slightly more fectly dry sample of coal, for example, is placed in a coffee, etc., using both desiccator containing CaC12, which has been used for moisture was obtained with vacuum t h a n without. In one instance i t was as much as 0.7 per cent and some time, or concentrated HzS04, the coal will increase in wcight. When the desiccator is opened in other cases quite small. The effect of a fairly large variation in thc concensome moisture enters from the atmosphere, t o be sure, b u t not enough t o account for the increase in weight tration of H2SO.1 changes the total amount of moisture removed from some substances very slight,ly; of the coal. in other cases, however, the change is marked. Table As compared t o the wide use t o which HzS04 and CaClz are p u t as drying agents for organic substances I shows the results obtained with flour, cane-sugar which cannot be heated, t h e literature on the sub- syrup and cheese dried t o constant weight over various ject is meager. The desiccating efficiency of sereral concentrations of HzS04. Each sample for each consubstances like CaC12, Ka, fused NaOH, PaOs, etc., centration was dried in an individual desiccator. TABLE I--EFFECT OF CONCENTRATXOX ON DRYING POWER OP HzSO4 has been tried. Baxter and Warren2 tried CaBrz, Atmospheric pressure and laboratory temperature ZnBre and ZnClz b y passing moist air over them. Total time of drying about three weeks Vapor pressure PSR CENTWATERIN They found t h a t HzS04 was more efficient t h a n any mm of H g c-----------’--------Per cent White flour Cane SYTUW &SO4 (aworoximate) of these, Johnson3 has published a note on the use . _. - - Cheese 95 ( 0.03)? 12.48 48.28 26.51 of A1203as a desiccating agent in which it is claimed 84.8 0.18 12.28 48.25 26.10 78.3 0.8 10.04 48.27 25.58 t h a t A1203is morc effective than H2S04 for removing 65.6 2.7 7.22 48.10 24.88 62.6 3.5 2.89 47.97 23.47 moisture from air saturated with water vapor. 37.0 15.0 0.10 47.30 21.18 I n t h e hope of suggesting a good substitute for the .,. 34.70 .. 29.6 17.5 21.9 20.0 ~ . . 22.01 ... time-worn CaC12, if not for HzS04, in ordinary desic15.2 21.0 ... 0.29 .0 22.5 ... 4 9 . 4 (inmemiin weight) cation, the present work was undertaken. Also, a Per cent7moisture found by drying at looa C. t o constant weight.. 1 1 . 8 5 49.78 26.65 series of experiments with H2SOd has been run to show Polariscope, . . . , . . . . , . . . . . . . . . . . 49.89 100 per cent(a) ~ 1 ~ 0 4 . . . . 1 i l i 5 4 8 . 2 8 26165 t h e effect of the concentration of the acid on drying ( a ) Values obtaiued by plotting percentage moisture against peecertain substances, and i t is hoped t h a t the results centage HzSO1. wiil throw some light on the vagaries o f as It will be seen from Table I t h a t cane syrup could a desiccant. Many analysts seem in doubt regardbe dried about as well, although, as laboratory ex1 This work was started in the laboratory of the South Dakota State ~
Food and Drug Department. J . Am. Chem. Soc., 33 (1911), 340 ’ a Ibid., 84 (1912), 912. f
l,.
~
~
19. Bid. Chem., 15, 259-61. * “Dictionary of Applied Chemistry,” mans, Green & Co.
Vol. 11, p. 210 (1912). Long-
