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Filter bottom tile are laid in mortar over a concrete slab completely covering the wetted area. The rate of feed to the filters is about 16 million gallons per acre per day with an average phenol content of 13 to 30 p. p. m. The effluent (0.4 to 3.0 p. p. m. of phenols) enters a 31-acre detention pond from which it flows to the river with less than 0.05 p. p. m. Temperature of feed to the filters must be 70” F. for this rate; lower temperatures necessitate slower rates, and below 50’ F., practically no action takes place.
Sediments Plant emuents carrying appreciable amounts of turbidity pass through ponds several feet deep spreading over 42 acres, where the greatest proportion of solids settle out and dissolved oxygen is restored to nearly saturation. A satisfactory disposal for solutions that may cause precipitates when mixed with one another or when mixed with river water is still being sought. Sulfur chloride and waste water precipitates a
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very fine sulfur when mixed with effluents from sulfur insecticide plants and carbon disulfide wastes. This is comparatively harmless but causes unsightly turbidity for long distances downstream from the plant. It may be possible to segregate most inorganic acids so that the main body of the wastes will not precipitate sulfur. Experimental work is now in progress toward a solution of this problem.
Atmospheric Pollution Chemical vapors such as chlorine, bromine, sulfur dioxide, hydrogen chloride, ammonia, sulfur dichloride, carbon disulfide, etc., are prevented from escaping to the atmosphere by scrubbing vent gases of all processes in towers with the proper absorbent (Figure 3). The value of products recovered often pays for the expense. Absorbents are the usual onesalkalies, acid, and charcoal. Odors from storage ponds may be a nuisance in warm weather. As an example, acid waste contacts alkaline sulfides and liberates hydrogen sulfide. Faulty operation of scrubber towers may do damage to lawns, trees, and shrubbery, may cause corrosion of steel equipment, discoloration and destruction of painted surfaces, and, with certain conditions of humidity and temperature, may cause fogs.
Biological Processes for Treating Waste A. M. BUSWELL University of Illinois and Illinois State Water Survey, Urbana, Ill.
Biological processes are applicable to wastes from industries using biological raw materials primarily. Three essentially distinct biological processes have been applied to the treatment of such industrial wastes : bioprecipitation which results in oxidation and precipitation, anaerobic fermenta-
HE purpose of this paper is to discuss certain biological processes which are broadly applicable to the stabilization of all organic wastes. The term “trade wastes” as ordinarily used applies to the water-carried wastes discharged by manufacturing plants. A few of these waste liquors carry mineral salts or acids which are responsible for more or less damage to the stream. By far the larger number discharge organic material of a biological origin which, on decomposing, causes putrefactive odors and a depletion of the oxygen of the stream below the requirements of normal fauna and flora. We are primarily concerned with this latter class of wastes in the discussion of biological processes in industrial waste treatment. The primary object of treatment processes is to prevent oxygen deficiency in the streams. Oxygen deficiency is the basic cause of nuisance and destruction of fish and other aquatic life as well as normal vegetable life. The elements carbon and hydrogen and to a small extent nitrogen are the chemical factors responsible for consumption of dissolved oxygen; therefore the problem is to remove substances containing unoxidized compounds of these elements.
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tion which converts organic matter to insoluble gases, and production of valuable by-products. Examples of the first two are discussed, and data are given to show limits of applicability and results obtained. The third type of process is largely in the experimental stage.
BACTERIA of various sorts are capable of accomplishing this in two ways-namely, to form relatively insoluble gases or solids from the carbon in the organic matter. These processes might be classified as fermentative (gas producing) and precipitating (bioprecipitating) A more common classification of the processes for biological stabilization is made o n the basis of the classes of bacteria and other microorganisms which are responsible for the results produced. This classification divides the stabilizing processes into the aerobic and anaerobic groups-that is, those produced by organisms requiring air or oxygen and those carried on in the absence of oxygen. Except in the case of very simple substances, such as acetic acid or glucose, aerobic and anaerobic action both yield solid and gaseous end products under practicable conditions. When carried to the extreme, the solids may be almost, if not completely, gasified by both processes. The character of the solids and gases is distinctly different in the two cases. The aerobic process naturally yields carbon dioxide, and the hydrogen forms water. The solids produced
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are largely microbial protoplasm together with colloidal and suspended matter (6,9,10,15) caught by the biological jelly. The solids amount to 60 to 70 per cent of the original material, the remainder being carbon dioxide and water. The anaerobic process yields a humuslike solid, and the gas evolved is composed of methane and carbon dioxide together with small quantities of hydrogen. The methane and carbon dioxide together usually amount to 95 per cent of the total gas collected, and the ratio of methane to carbon dioxide varies from 1:1 to 3:l (1, 1,3, 19, 10,21, ZS), depending on the composition of the material decomposed and to a lesser extent on the conditions under which the fermentation is carried out. The humuslike solid material remaining a t the end of active anaerobic fermentation may amount to 40 per cent of the original when woody material is decomposed; but relatively simple and less resistant substances such as sugars, fats, and certain proteins are completely gasified (2, 7, 8, 11, 17). Considerable data are available in the literature cited above which indicate that, with the exception of hydrocarbons, practically all carbonaceous substances can be quantitatively converted to methane and carbon dioxide if they are fermented long enough and under proper conditions. Even lignin yields slowly to this action (3). Both of these processes effectively accomplish the stabilization of putrescible waste liquors. The choice between the two will depend on the particular problem involved. Where conditions permit its use, the anaerobic process is much cheaper per pound of organic matter stabilized. A good example is the calculation made in our laboratory to show the relative cost of treating dairy wastes by anaerobic fermentation and on trickling filters (6). On the basis of an average dosage of one twenty-fifth of a volume of milk waste (undiluted basis) per day per tank volume, it would require a tank, or tanks if operated as a twostage process, of 5.72 cubic feet capacity for the anaerobic fermentation of one pound (dry weight) of milk waste solids. At 50 cents per cubic foot, this amounts to only $2.86 per pound of milk solids treated. This fermentation would remove at least 95 per cent of the pollution load. The remaining 5 per cent contained in the overflow liquor could be stabilized readily on filters. Assuming that this final treatment could be made a t a cost similar to that given for filter treatment in the first portion of the paper, the total investment for complete treatment would be $8.70 per pound of solids if trickling filters were used following the anaerobic digestion, or $17.46 per pound if sand filters were used, as compared with $116.80 per pound if trickling filters were used alone, or $292 per pound if sand filters were used. The above figures are not given to show actual costs but rather relative costs of the two processes (7). The anaerobic process requires simple covered tanks of suitable design. Although this process is much less expensive, it has two serious limitations. First, for reasons as yet obscure, it is impossible to produce a final effluent comparable to that yielded by aerobic treatment. The discharge from anaerobic fermentation is usually dark colored and rather foul with a B. 0. D. of several hundred parts per million. Where a high dilution is available, this is not a serious handicap, and where heavy untreated wastes are being discharged, the 75 to 90 per cent reduction in the B. 0. D. load effected by anaerobic treatment produces such a great improvement that i t may be adopted as a preliminary measure. As will be mentioned in more detail below, the anaerobic process may be used as a preliminary step followed by the more ertpensive aerobic process where necessary. The second limitation is that the cost of anaerobic treatment increases as the concentration of the waste decreases. This is due to the large tankage re-
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quired to accommodate a given number of pounds of organic matter when dilute liquors are to be handled. We have usually found that the economics of the process disappear when wastes containing less than one per cent organic matter dry weight are to be treated. There is no upper limit of concentration to this process. The aerobic process is carried out in two types of structures-open rock beds over which the liquid trickles (trickling or sprinkling filters) or tanks provided with air diffusers (activated sludge tanks). I n one type the capital cost is high and the operating cost low; in the other the capital cost is low but the operating cost high. I n both cases the total cost per pound stabilized is of the same order of magnitude. This process produces a high-quality effluent with a low color and B.0. D. It can usually bedischarged into a stream of very low flow without causing nuisance. Aside from high cost, the aerobic process is limited first by its inability to treat liquids of high concentration and secondly by its inability to handle coarse solids. When trickling filters are used with concentrated liquids, they become clogged and activated sludge tanks become septic. This difficulty has largely been solved by recirculation of the treated effluent to dilute the incoming raw waste. From five to ten volumes are sometimes recirculated in this manner. The trickling filter is a t present in s m e w h a t greater favor than activated sludge for treating heavy wastes and has recently been used in connection with recirculation although it is a very old practice (19). It has recently been combined with continuous flow with excellent results by Halvorson (12, 13, 14, 11). Loadings are increased approximately t h e e - t o sixfold,
AN example of a combination of anaerobic and aerobic treatment together with recirculation was described previously (7). This experimental plant treated distillery wastes of about 3 per cent solids and turned out a high-quality effluent. The process consisted essentially of passing the slop through two digestion tanks in series and applying the digested effluent, diluted with a part of the finally purified waste, to a trickling filter. The flow through the digestion tanks was as follows: The raw thin slop was pumped to the cooling and feed tank. Although provision was made in this tank for cooling the slop to the proper temperature (130" F.), the cooling facilities were seldom used. The heat of the slop could ordinarily be utilized in heating the first tank. After a dose had been measured and sampled, it was allowed to flow into the primary digestion tank. This tank was heavily loaded, accomplishing the greater part of the digestion and yielding most of the gas generated. From the primary tank the partially digested slop was forced by succeeding doses to a secondary digestion tank where further digestion a t a decreasing rate was accomplished. A back-circulation pump made it possible to return liquid from the secondary tank to the primary tank for seeding and dilution. This is an important control measure which, in conjunction with other control tests, made it possible to place loadings on the primary tank which were of the order of ten times those used in common sewage-sludge digestion practices. A 1000-gallon, digested-liquid overflow tank made it possible to place the full 24-hour load on the filter in 8 hours or during one shift. The trickling filter, which required little or no attendance, was operated a t a constant rate over the 24 hours; the necessary equalizing storage was furnished by the 1000-gallon overflow tank. The trickling filter operation was as follows: Dilution of some sort had to be provided in the design of the trickling filter in order to reduce the oxygen demand of the liquid supplied to the filter. If a t the same time this dilution
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could result in a reduction of the odors, the filter could be operated without causing a serious nuisance. The trickling filter was constructed in a circular steel tank. The stone bed was 9 feet in diameter and 7 feet deep. Although the filter was of an experimental nature, its size would be sufficient for a small dairy and could almost be considered a plant-scale demonstration. The effluent from this trickling filter was used to dilute the digester effluent. This idea was used elsewhere in treating a concentrated industrial waste (18). In order to accomplish the desired result, the effluent from the trickling filter was discharged into a small box with two outlets. One outlet led to a final sedimentation tank, the overflow from which was the final efffuent. The other outlet led to a diluting-liquid sedimentation tank. The discharge line from this tank was conducted to the suction of the trickling-filter pump. Also connected to this suction was the digested distilleryslop feed line. By this arrangement the filter pump dosed the trickling filter a t a rate equal to a rate of raw feed plus a quantity of trickling-filter effluent. For example, when the filter pump was operated a t a rate of 2 gallons per minute and digested distillery slop was fed a t a rate of 0.5 gallon per minute, the pump automatically made up the difference (1.5 gallons per minute) from the diluting liquid sedimentation tank. With the arrangement used the feed could be turned off entirely, in which case the pump would take its entire pumpage from the diluting-liquid sedimentation tank. A closed system would result, the trickling-filter effluent being pumped in its entirety onto the trickling filter again and again. The sedimentation tank was installed for removing settleable solids from that portion of the trickling-filter effluent used for deodorizing and diluting the feed of digested distillery slop. This was important in reducing the amount of suspended matter put on the trickling filter. As a consequence no troubles due to filter clogging were encountered.
WHERE coarse solids are to be treated, a special tank is required. This was used for the anaerobic treatment of paunch manure. The feeding end of the tank is provided with a spout extending through an opening in the tank end wall within the circle formed by the seal ring. The material to be treated may thus be fed directly into the open end of the drum adjacent to the feeding spout. A discharge opening is provided in the lower portion of baffle wall to permit undecomposed material from the drum to pass out into the discharge compartment. Material discharged into the compartment is withdrawn in any convenient manner. The fermentation compartment is fitted with a gastight cover provided with a gas vent having a tight cover or removable hood resting in a water seal. The water seal prevents the entrance of air into the digestion compartment where the fermentation takes place and also the escape of gas. It likewise prevents the building up of excessive pressures within the digestion chamber and tends to keep a uniform, slight pressure therein. A pipe from the collecting hood serves to draw the gas out into a suitable reservoir or any device in which the gas may be used or stored. The drum is rotated or inverted a t least twice a day, or continuously if desired. This releases the entrapped gases, and the tank contents are sufficiently mixed to prevent local accumulation of acids. The writer has found the turning over of the drum and the periodic feeding a t the front end of the tank to be sufficient to cause the fermented material t o work itself out through the opening in the baffle into the residue end of the tank. Here it continues to ferment slowly, and again gas bubbles are entrapped and the material is brought to the surface where it can be removed with a hay or manure fork or by a continuous device. The design and operation of this type of tank are described in a patent (4).
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MENTION should be made of the fact that phenols are decomposed by both aerobic and anaerobic action’ (16). It appears that these substances do not interfere with conventional treatment methods unless introduced in excessive quantities. Fifty to a hundred parts per million of phenols have been treated without interrupting the operation of the bacteria. I n conclusion we may say that all types of organic wastes are amenable to biological treatment. Complete purification is feasible, and in the case of certain wastes the anaerobic process yields a valuable quantity of methane as a byproduct.
Literature Cited Boruff and Buswell, IND. ENG.CHEM.,21, 1181 (1929). Ibid., 22, 931 (1930). Boruff and Buswell, J. A m . Chem. SOC.,56, 886 (1934). Buswell and Boruff. U. S. Patent 1,880,772 (Oct. 4, 1932). Buswell, Boruff, and Wiesman, IR‘D. ENG.CHEM.,24, 1423 (1932)., Buswell, Brensky, et al., Illinois State Water Survey, Bull. 18, 7 (1923). Buswell and LeBosquet, IND. ENG.CHEM.,28,795 (1936). Buswell and Neave, Illinois State Water Survey, Bull. 30 (1930). Buswell, Shive, and Neave, Ibid., 25,5 (1928). Buswell, Strickhouser, et al., Ibid., 26, 21 (1928). Buswell, White, Symons, et al., Ibid., 29 (1929). Halvorson, Water Works & Sewerage, 83,307 (1936). Halvorson, Savage, and Piret, Sewage Works J.,8, 888 (1936). Halvorson and Smith, U. S. Patent 2,141,979 (Dee. 27, 1938). Johnson, J. Econ. Biol., 9, 105-25,127-63 (1914). Kalabina, M., and Rogovskaya, C., 2. Fischerei, 32, 152-70 (1934). Larson, Boruff, and Buswell, Sewage Works J., 6, 24 (1934). Naylor, “Trade Wastes”, p. 153, London, Charles Griffin & Co., 1902. Neave and Buswell, Ill. State Water Survey, Circ. 8 (1930). Neave and Buswell, J . A m . Chem. SOC.,52,3308 (1930). Piret, Mann, and Halvorson, IND. ENG.CHEM.,31, 706 (1939). Symons and Buswell, Ibid., 55, 2028 (1933). Tarvin and Buswell, Ibid.,56, 1751 (1934).
Courtesy, Carnegie-Illinois Steel Corporation
UPTAKES AND DOWNCOMER PIPES(A) INTO BLASTFURNACE DUSTCATCHER (B) WHEREFLUEDUSTIs RECOVERED. (See text on page 1366.)
