Jan.,
1916
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
VI-The rate of polymerization for wood oil is considerably faster than for linseed oil at corresponding temperatures, taking place completely in one hour at 2 j o ' C. A t I joo C. only about 72.4 per cent polymerization takes place in 66 hours. VII-Wood oil is subject t o decided oxidation when heated in air. Progressively increasing amounts of oxidized materials are formed whenever wood oil or wood-oil mixtures are heated in the air. VIII-Lime, litharge and oxidation products catalyze t h e polymerization of the elaeomargaric acid triglyceride into t h e intermediate product. Oxygen does not catalyze the rate of polymerization except indirectly through t h e oxidation products. A large number of metals also act as positive catalyzers at the higher temperatures. IX-The course of polymerization can be followed b y t h e iodine number alone and does not require correlating with t h e specific gravity and refractive index. X-Dissolving t h e solid gel in rosin or continually heating i t above 2 jo' C. constitutes a reformation of t h e soluble intermediate products. In tlie latter case considerable decomposition occurs, the products of which are responsible for t h e breaking down of the molecular complexes of t h e polymerized tri-glyceride. This decomposition is considerable on heating wood oil or wood oil mixtures above 2 5 0 ' C. for a n y length of time, and is accelerated b y t h e presence of certain metals. XI-The darkening of rosin or rosin-chinawood oil mixtures on heating in air is primarily due to the decomposition products from t h e oxidized oil, which are very sensitive t o temperatures above 175' C. This decomposition may be largely avoided by carrying out t h e heat treatment out of air. This is also applicable to the manufacture of chinawood oil driers. XII-The pure polymerized product of chinawood oil dries very slowly, as might be expected from t h e small iodine number. This slow rate of drying characterizes such rosin-chinawood oil varnishes as contain large percentages of polymerized tri-glyceride. I t is with great pleasure t h a t acknowledgment is made t o Professor E. E. Ware for his interest in this work and for his valuable suggestions and criticisms.
15
The tanks are located in thc basement of thc University power plant (see Fig. I ) . T h e room is not affected by heat from t h e boilers and conditions are similar to those which would bc obtained by housing a plant. I t was very easy t o t a p the city of Champaign main sewer which passes underneath t h e coal hopper (Fig. 11) of t h e power plant. The sewage is pumped t o the tanks by a 2 H. P. centrifugal pump run by a direct connected motor. Each tank is 3 ft. 2 in. squarc, having an area of I O sq. ft. Each tank is 8 ft. j in. in depth above I1/?-in. Filtros plates which are used for diffusing t h e air. I n 2 tanks there are 9 plates, each 1 2 in. square, covering the entire floor. I n the third t a n k there are 3 plates, covering the area of the floor, forming the
U ~ r v a ~ o r rOP v MICHIDIN.ANN Aison
PURIFICATION OF SEWAGE BY AERATION IN T H E PRESENCE OF ACTIVATED SLIIDGE-II By Bowrao BARTOW A N D F. W. MOHLXAN Received December 13. 1915
Since reporting the results of our preliminary work, experiments' on purification of sewage b y aeration in the presence of activated sludge have been conducted on a larger scale. Four reenforced concrete tanks have been completed a n d p u t in operation. These tanks, operating on the fill and draw system, are designed for studying in a comparative manner t h e amount of air required, t h e best method for distributing t h e air, the time required for purification, and the quantity and quality of activated sludge formed. I
Tars Jousn~r.7 (1915). 318.
bottom of a central trough. The remainder of t h e bottom slopes t o t h e plates a t an angle of 4 j 0 . I n the fourth tank is a single plate in t h e centcr covering one-ninth the area with t h e bottom sloping to i t at an angle of 4 j " from all sides. Below the plate is a n air space 4 in. deep. A pet cock is provided t o relieve the air pressure when draining the tank and to prevent air bubbles from rising and stirring up the sludge. The air obtained from the University compressed air plant at a pressure of 80 Ibs. is reduced b y a pressure reducing valve t o 8 Ibs. and is further regulated b y a hand-operated valve before passing through meters on each tank. T h e pressure under which it enters the tank is sufficient only t o overcome the pressure
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THE J O U R N A L OF INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
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of the sewage, equivalent t o about 8 in. of mercury, or, a little less t h a n 4 lbs. per sq. in. Two outlets for the effluent are, respectively, 2 f t . 6 in. a n d j ft. 7 in. above t h e porous plates. A t a n k can be filled in 6 minutes and drained t o the lower outlet in 8 minutes. Experience has shown t h a t a lower outlet connected t o a floating outlet would be preferable. A fixed outlet is objectionable because sludge is a t times drawn out with the effluent. I n fact, no accurate d a t a have been obtained concerning the quantity of sludge formed, because we have been unable t o determine how much has been lost with t h e effluent. In order t o prevent this loss, a floating outlet made of n-in. pipe connected together with loose joints, has been placed in t a n k C. The effluent flows t o t h e outlet through a screen of copper wire of about 16 mesh,
aerated until it is aerobic and similar t o activated sludge. Such a source of sludge would not be available in many places, especially a t newly installed plants. We have attempted t o shorten t h e period of sludge formation. Tanks A and B were filled with t h e same kind of sewage on M a y j , 1915. The sewage in t a n k A was aerated continuously; the sewage in t a n k B was aerated 2 3 hours, allowed t o settle, t h e supernatant liquid withdrawn and refilled with fresh sewage in one hour. This cycle was repeated daily and determinations of t h e amount of sludge and of t h e degree of purification were made daily. A t t h e end of I O days, after one hour's settling in Imhoff cones, 1.0 per cent of the volume in A consisted of sludge while about I O per cent of t h e volume in B n-as sludge. The effluents from 4 , which had El
which is fastened on both sides of a n iron frame I ft. square. With this arrangement no sludge has been lost and we expect t o obtain accurate d a t a concerning t h e amount of sludge formed from t h e sewage. The amount of sludge must be determined b y weight on the dry basis for it has been noted t h a t its volume a n d rate of settling r a r y with t h e amount of air applied. If a n unusually large amount of air has been applied, the sludge will settle more slowly and will occupy a much greater volume even after prolonged settlement, than it does when less air has been applied. B U I L D I K G CP O F SLUDGE-If, in accordance m-ith previous practice, activated sludge is built up b y complete nitrification of each portion of sewage added, it would require several weeks t o put a plant in operation. I n order t o obtain sludge more quickly t h e English investigators have used sludge from sprinkling filters. ,4t Milwaukee, Imhoff t a n k sludge has been
been aerated I O days, and from B , which had been aerated one day, were equally stable while t h a t from B was clearer. T a n k B was continued in operation, changing t h e sewage every 2 4 hours, until. after I j days, nitrification mas complete. Then t h e sewage was changed every 1 2 hours; nitrification was again complete after 8 days. T h e n the sewage was changed every 6 hours; many of the effluents with the 6-hour cycle were putrescible and i t is necessary a t intervals t o aerate for longer periods. This comparison indicated, however, t h a t sludge may be satisfactorily activated by changing the sewage before nitrification is completed, and t h a t t h e sewage may be changed a t frequent intervals. T a n k A was, therefore, cleaned and fresh sewage added every 1 2 hours. Stable effluents were obtained in 7 days; complete nitrification occurred in 18 days, after which t h e sewage was changed every 6 hours.
Jan., 1916
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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The effluents obtained from t h e tanks during this ages are t o be treated a definite cycle of operation 6-hour cycle were not all stable, yet t h e average im- cannot be established without provision for longer aeraprovement was so great t h a t t h e conclusion was reached tion of the sewage or separate aeration of t h e sludge. t h a t activated sludge may be built up b y changing I n order t o keep t h e sludge in its most active state, sewage a t frequent intervals without complete nitri- complete nitrification of each sewage is necessary. fication of each dose of fresh sewage. A considerable Effluents are usually stable if 50 per cent of the free degree of purification is also obtained from t h e be- ammonia is removed, and 2 t o 3 parts per million ginning of t h e operation, and t h e time for building of nitrogen as nitrates are present. A completely nitriup adequate sludge for t h e process is cut down very fied effluent is neither necessary nor economical. The greatest efficiency in air consumption will be decidedly. A later experiment with t a n k C showed t h a t satisfactory activated sludge could be built upon obtained when enough air is used t o make t h e sewage non-putrescible and t o keep t h e sludge activated. a 6-hour cycle. The operation of t h e plant during six months has sugD I F F U S I O K A R E A REQUIRED-The bottom Of t a n k contains 3 sq. f t . of Filtros plates as described above; gested t h e advisability of studying more carefully the bottom of tank D contains I sq. ft. These such other features of t h e process as t h e amount of tanks were p u t in operation July 6th and t h e sewage sludge formed, t h e building up of nitrogen in t h e sludge was changed every 6 hours. There was a noticeable and the composition of t h e effluent gases. difference in t h e working of these tanks. C gave some STATE WATBRSURVEY U N I V E R S I T Y OF ILLINOIS. URBANA stable effluents after 5 days; D did not give stable effluents in 18 days. The sludge from C was of good appearance, while t h a t from D was not as flocculent FERTILIZER VALUE OF ACTIVATED SLUDGE’ a n d at times had a septic odor. During t h e comparaB y EDWARD BARTOW AND W. D. HATFIBLD tive experiment a n average of 450 cu. ft. of air per Activated sludge is a n essential material a n d a n 400 gallons of sewage was used with C and of 360 CU. important product in a new method of sewage disposal, ft. of air per 400 gallons of sewage with D. The amount which was first described by Ardern and Lockett12 of of air given D was always sufficient t o keep the sludge Manchester, England, in 1914. mixed with the sewage. I n fact, the sewage in D At present, September, 1915, experimental plants was agitated much more violently t h a n t h a t in C. are being operated at Baltimore, Md.; Chicago, Ill.; We have concluded t h a t I sq. ft. of Filtros plate per Cleveland, 0.; Houston, Tex.; Milwaukee, Wis.; I O sq. f t . of floor area is hardly sufficient. Of t h e four New York City; Regina, Saskatchewan; Urbana, Ill. ; tanks, C , with 3 sq. ft. of Filtros plate per I O sq. ft. and Washington, D. C.3 At Baltimore a modified of floor area, has given t h e best results. Imhoff t a n k is t o be operated with continuous flow. At We have noted t h a t it is quite essential t h a t t h e Milwaukee both fill and draw and continuous flow plates be as nearly as possible a t t h e same level. A processes are being operated on a n experimental variation of in. in level will cause uneven air dis- scale, and a z,ooo,ooo gallon plant is under constructribution. The distribution seems t o become more tion. At Cleveland a I,OOO,OOO gallon plant is t o uniform t h e longer t h e plates are used. be built. At Urbana a n experimental plant of 6,000 Q U A L I T Y O F EFFLuENTs-The quality Of t h e effluents gallons capacity is being operated on t h e fill and draw has usually depended more on t h e strength of t h e raw system. sewage t h a n upon any other variable. The tanks, As in other sewage disposal processes, t h e ultimate when operating on a 6-hour cycle, were filled a t 9 A.M., disposal of t h e sludge is of great importance. Near 3 P . M . , 9 P.M., and 3 A . M . The strength of t h e raw sewage, t h e seaboard it is possible t o carry this sludge out t o estimated b y t h e free ammonia values, averaged for sea, but in t h e interior, t h e problem of sludge disposal t h e 9 A.M. sewage between 20 and 2 5 parts per million, is often very serious. for the 3 A . M . sewage between 3 and 1 2 parts per milI n the experimental plant at the University of lion. Nearly all of the 3 A.M. sewages have given Illinois, in Urbana, we have tried t o study all phases stable effluents, b u t t h e strong morning sewages of t h e process14 a n d have paid especial attention t o have quite frequently given putrescible effluents. t h e sludge. Unless the sludge is in good condition, a n d well nitriThe amounts of sludge formed a n d its chemical fied, a strong sewage cannot always be purified in corhposition evidently vary with t h e concentration 4 ’ / 2 hours even b y increasing t h e air to 800 cu. f t . per of the sewage, a n d with temperature conditions. 400 gallons. I n t h e normal working of t h e plant t h e The sewage treated in t h e experimental plant during sludge will usually regain its “activity” if 800 cu. ft. rainy weather contains large amounts of diluting of air is applied for several periods after t h e strong water, which reduces t h e amount of sludge per unit sewage has been added. of water. The diluting water carries considerable At times, however, with a succession of strong sew- dirt from the streets which reduces t h e nitrogen conages, it is necessary t o increase t h e time of aeration tent of t h e sludge obtained. Also during warm in order t o obtain good effluents. Ardern and Lockett’ weather, bacteriological action is more rapid, and, noted in their first paper that if t h e aeration was stopped 1 Presented a t t h e j l s t Meeting of t h e American Chemical Society, before t h e sewage was well nitrified, t h e activity of Seattle, August 31-September 3, 1915. * J. SOC.Chsm. I n d . , 33 (1914). 523, 1122. t h e sludge would be inhibited. When strong sew-
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a Eng.
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J . SOC.Chern. Ind.. 33, 623-39.
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News, 74, 164-70
THISJOURNAL,
7 (1915), 318.
