April 1950
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INDUSTRIAL AND ENGINEERING CHEMISTRY
line and the cock. By simply opening and closing these twice a week, the build-up is flushed out before i t has had a chance to cake. Initial operation was instituted with controls set at 2.3 and 3.5 pH. It was found t h a t the initial dosage was too high and that there was a wide spread in the secondary control varying from 3.0 t o 8.0 pH. However, duo t o poor operation of the secondary sanipling pump, it was never certain whether this spread was due to control or sample. I n time the authors gradually adjusted both control points downward and found t h a t 2.0 and 3.0 were about right. Sample pump troubles still clouded the issue and, for a time, it was necessary to run with only the control in the third chamber. With this method of operation, this control had to be set at about 3 and the effluent values had to be checked a t the end of the sewer. The control was not too good and a spread of about 1.5points below and 5 above was noted. With the installation of the first immersion electrode, the control in the fifth chamber was brought into line and the only troubles were pump outages in the No. 3 chamber. When the second immersion electrode was installed, pump troubles vanished and the controllers began t o function properly. Figures 10 and 11 are portions of chart records which show the typical effect of the pH control with rate action. Here the average band width at the first control is 0.3 p H unit wide (Figure 10) and the second 0.2 p H unit wide (Figure 11). The authors feel that this equipment is providing excellent control and that they are obtaining complete neutralization of thc effluent. While the p H value of the effluent leaving the reaction chamher is about 3, the pH
605
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value has risen to 4.5 leaving the plant proper, and is 5.0 entering South River. This is due t o the lower reaction rate of the dolomitic lime and thus necessitates the lower control setting. This control assures that all mineral acidity has been neutralized. These values have been obtained by adequate sampling at both these points and correlating with the chart records. As a further check on the operation of the equipment, titration of residual acid has been made on many samples of the effluent from the reaction chamber and thesc havc varied from 0 t o 200 parts per million (p.p.m.) as sulfuric acid, indicative of good control. The operation of the whole trcating system, including labor for unloading of the burned lime from box car t o storage bin, is adequately handled by one man per shift. It is not felt t h a t t h e labor required is excessive considering the magnitude of the installation. CONCLUSION
The authors believe that they have evolved a satisfactory and economical method for ncutralizing a widely fluctuating acid waste. They have been able to hold the effluent a t a satisfactory p H level so t h a t its effect on the receiving stream is negligible, and a one time source of aggressive pollution has been eliminated completely. LITERATURE CITED
(1) Jacobs, H. L., Chem. Eng. Progress, 43, 247 (1947). RECIOIVED December 12, 1949.
OPERATION OF ANAEROBIC FERMENTATION PLANTS A R T H U R M. BUSWELL Illinois State Water Survey Urbana, Ill. H E term “tradewastes” Anaerobic fermentation plants for the reduction of solids from the carbon in as ordinarily used apB.O.D. of organic wastes are capable of continuous operathe organic matter. These plies to the watertion for indefinite periqds. Loadings of 0.14 pound per processes might be classificd carried wastes discharged cubic foot per day of organic wastes have been found feasias fermentative or gas proby manufacturing plants. ble in many pilot plant studies. Existing plants built ducing and precipitating The purpose of this paper with a large safety factor are loaded to 0.1 pound per cubic (bioprecipitation), respecis to discuss certain biofoot per day and regularly produce a 70 to 80Yo improvetively. A more common logical processes which, ment in the quality of the waste. classification of the procbroadly speaking, are appliosses for biological stabilicable to the stabilization of zation is made on t h e all organic wastes. A few of these waste liquors carry mineral basis of the classes of bacteria and other microorganisms which salts or acids which are responsible for more or less damage to the are responsible for the results produced. This classification distream. By far, the larger number discharge organic material of vides the stabilizing processes into the aerobic and anaerobic a biological origin which on decomposing causes putrefactive groups-that is, those produced by organisms requiring air o r odors and a depletion of the oxygen of the stream below the reoxygen and those carried on in the absence of oxygen, quirements of normal fauna and flora. It is obviously this latter Except in the case of very simple substances like acetic acid o r class of wastes which are of primary concern in a discussion of the glucose, aerobic and anaerobic action both yield solid and gaseous biological process in industrial waste treatment. end products under practicable conditions. When carried t o t h e The primary object of treatment processes is to prevent oxygen extreme, thc solids may be almost if not quite completely gasified deficiency in streams. Oxygen deficiency is the basic cause of by both processes. nuisance and destruction of fish and other aquatic life, including The character of the solids and gases is distinctly different in normal vegetable life. The elements carbon and hydrogen and, the two cases. The aerobic process naturally yields carbon dioxto a small extent, nitrogen are the chemical factors responsible for ide, the hydrogen forming water. The solids produced are largely consumption of dissolved oxygen; so the problem is to remove microbial protoplasm together with colloidal and suspended matsubstances containing unoxidized compounds of these elements. ter (6, 8, 9, I S ) caught by the biological jelly. The solids amount Bacteria of various sorts are capable of accomplishing this in to 60 to 70% of the original material, the remainder being carbon two ways-namely, to form either relatively insoluble ga..qes or dioxide and water.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
606 Table 1. Location
Waste Volume of flow, gal./ day T a n k capacity, gal. yola@ solids, Yo i5.U.U.
Raw, unit Effluent, unit Removal, % Loadings, lb./cu. f t . / day Gas, cu. ft./lb. Vol. per t a n k vol.
Anaerobic Digestion Loadings
Pekin, Ill.
Peoria, Ill.
Crystal Lake, Ill.
Yeast (molmses)
Butapol (grain)
Yeast (molasses)
222,300 2,200,000 1.05
300,000 3,000,000 3.0
160,000 623,000 0.7
10,000 2,000 80
17,000 2,420 69.8
5,000 1,500 70
0.108 5.0 0.525
0.114
0.104
9.3 1.06
4.25 0.43
Jefferson Junotion, Wis. Trickling filter sludge 2,000
40,000 3.5
Carthage, Ohio Distillery (grain) 500 7,200 3 16,000 1,600 90
0.10 9.2 1.0
0.143 11.0 1.5
~
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 95y0 of the total gas collected, and the iatio of methane t o carbon dioxide varies from 1: 1 to 3: I ( I 8,16, 17, 19, $0) depending on the composition of the material decomposed and to a lesser extent on the conditions undei n hich the feimentation is carried out. The humuslike solid mateiial iemaining at the end of active anaerobic fermentation may amount to 40% of the original when woody material is decomposed, whereas relatively simple and less resistant substances surh HS sugars, fats, and certain proteins are completely gasified (2. 6, 7 , 10, 16).
Considerable data, available in the literature clted above, indicate that, with the exception of b-drocarbons, practically all catbonaceous substances can be converted quantitatively to methane and carbon dioxide 11 fermented long enough and uridei proper conditions. Even lignin yields s l o ~ l yto this action (3). Both of these processes effectively accomplish the stabilizatiori of putrescible waste liquors. The choice between the two will depend on the particular pioblcm involved, Wheie conditions peimit its use, the an Aerobic process is much cheaper per pound of organic matter stabilized. A good example is the calculation made in this laboratory t o shoA the relative cost of treating dairy n astes by anaerobic fermentation and on trickling filters. The anaerobic process requires simple covered tanks of suitable design for its use. On the basis of a n average dosage of one twenty-fifth of a volume (undiluted basis) of milk waste ( 4 ) per day per tank volume, i t would requiie a tank, or tanks if operated as a two-stage process, of 5.72 cubic feet capacity for the anaerobic fermentation of 1 pound dry weight of milk waste solids. -4t 50 cents per cubic foot, this amounts to only $2.86 per pound of milk solids treated. This feimentation would remove at least 95% of the pollution load. T h e remaining 5% contained in the overflon liquor could be stabilized readily on filteia. Assuming that this final treatment could be made a t a cost similar to that given by Kimberly (14)for filter treatment of milk wastes, 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. This is comparable to $116.80 per pound if trickling filters XT ere used alone, or $292.00 per pound if sand filters were used alone. These figures are not given to show actual costs, but rather relative costs of the two processes (8). Although the anerobic process i b much less expensive, i t has two serious limitations: f i s t , for reasons a s yet obscure, it is impossible to produce a final effluent comparable t o that yielded by aerobic treatment. The discharge from anaerobic fermentation is usually dark-colored and rather foul with a B.O.D. of several hundred. Where a high dilution is available this is not a serious handicap, and where heavy untreated wastes are being discharged
Vol. 42, No. 4
the 75 to 90% reduction in the B.O.D. load cfl'ected by anaerobic treatment produces such a great improvement that it may be adopted as a preliminary measure. As will be mentioned in more detail later, the anaerobic process may be used as a preliminary step followed by the more expensive aerobic process where necessary. The second limitation is that the cost of anaerobic treatment increases a8 the concentration of the waste decreascs. This is due to the large tankage required to accommodate a given number of pounds of organic matter when dilute liquors arc t o bc handled. Usually the economic advantages of the process disappear when wastes containing less than 1% organic matter dry weight are to be treated. There is no upper limit of roncentration to this pi'ocess. However, when the concentration of the waste reaches 3y0,i t can usually be evaporated and dried a t a cost which permits its profitable sale as a stock food or as a fertilizer. The preferred design for a n anaerobic fermentation plant consists of two or, bet'ter, three tanks with floating covers arranged to operate in series. Fixed-cover digesters do not offer the desired flexibility in altering the relative volumes of digesting liquor in the different tanks. The necessity of drawing air into u fixed-cover digester xhen removing liquor creates a n explosion hazard (1R, 18). h heat exchanger is necessary to m:tirltain the desired temperature-about 95" F. for rold wastes and 130" F. for hot wastes. The floating covers are conical and carry donics for gas collection. These are protected by flame traps. The bottoms of the tanks are conical, sloping 1oward the center. The circulating pumps :tnd piping system must be laid out to provide the following variations in a three tank system: 1. Use of the series in any order: 1, 2, 3; 2, 3, 1; 3, I, 2; or 3, 2, 1. 2. Circulation of contents of each ta.nk from bottom or centcr t o center or top. 3. Circulation of the contents of any pair of tanks or all three tanks in a similar manner.
The laigest plant constructed to date is at Pekin, Ill. The following design data are taken fiom a report by RIetcalf and Eddy, consultants ( 1 1 ) : The weekly average volatile solids content of the four major wastes to be treated by anaerobic digestion ranged from 0.79 t o 1.36%, averaging 1.05% for the 93 weeks ending January 1, 1938. The average quantity of these wastes during this period was 222,300 gallons per day, 6 days a week, the &day average for the week of maximum flow being approximately 320,000 gallons per day. The digestion capacity of the six digestion tanks to be built will be approximately 285,000 cubic feet not including the space reserved for ga;s but including an allowance of 10% for accumulation of sludge. rhe effective digestion capacity is accordingly approximately 259,000 cubic feet. The average 6-day loading for the 93-week period with an average of 222,300 gallons per working day, and an average of 1.05% volatile solids, would be 0.075 pound per cubic foot per working clay, An additional digestion period of 1 day per week with little or no wastes added is accordingly afforded. The loading based on the maximum average flow per working day for 1 week and the average of 1.05% of volatile solids would be 0.108 pound per cubic foot per working day. The maximum loading based on the average flow per working day for the week of maximum flow and the maximum weekly average of 1.36% of volatile solids, which combination 1%-ouldrarely if ever occur, would bc 0.140 pound per cubic foot per working day. This report points out that in the anaerobic digestion tests excellent results were obtaiiied with loadings as high as 0.3 pound per cubic foot of digestion flask capacity after favorable biological action had become established. Originally, four digestion tanks were proposed, having a n effective total digestion capacity of 170,000 cubic feet, which allowed a considerable factor of safety for the loading of the large digestion tanks in practice. In order to make it possible to maintain high efficiency in case of continuous operation of the factory at capacity production, it was decided to provide six tanks instead of four, thus increasing the digestion capacity by 50% and also increasing the flexibility of operation.
April 1950
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Table I summarizes extensive performance data based on several years of operating experience. Column 1 shows the usual performance of the Standard Brands yeast plant at Pekin, Ill. The purification amounts to 80% a t a loading of 0.10 pound per cubic foot per day. Since the thirdstage tanks show practically no improvement over the second stage, the effective load is 0.15 pound per cubic foot per day. This plant has been in continuous operation for 10 years. Column 2 shows the performance of digesters operated by the Peoria Sanitary District while digesting the “slops” or “still bottoms” from the Commercial Solvents butanol-acetone plant. The digesters, which have been in operation for about 15 years except for a few periods when the butanol plant was shut down, are accomplishing a 69.8% reduction in B.O.D. at a loading of 0.114 pound per cubic foot per day. Column 3 shows the normal operating results of a plant a t Crystal Lake, Ill,, put into operation in 1944. This plant consists of a two-stage digester for handling wastes from the manufacture of yeast. The waste is slightly more dilute than that .at Pekin and the loading is correspondingly less, a s is the gas yield. The removal of B.O.D. is 70%. The primary digester is equipped with a floating cover and has a capacity of 366,500 gallons. The secondary digester has a fixed cover and a capacity of 264,300gallons. The data in column 4 were obtained on a n installation treating the wasted steep water from a malt manufacturing plant. The steep liquor is free from suspended solids and is discharged directly to a trickling filter. The filter “unloads” continuously and passes to a settling tank which is provided with mechanical sludge removal. This sludge is digested in two 20,000-gallon digesters equipped with floating covers. The effluent from the digesters is returned t o the influent to the trickling- filter. The sludge is di’ gested until i t drains well on sand beds.
607
Although results in column 5 were obtained on a two-stage pilot plant operated for about 4 months, they are believed to be representative of what can be acconipiished under carefully controlled conditions. Ninety per cent purification was obtained with a loading of 0.143pound per cubic foot. This pilot plant experiment has previously been described in detail (6). ACKNOWLEDGMENT
The author wishes to thank L. 5.Kraus who furnished the performance data on the Commercial Solvents butanol-acetone plant, and M. W. Tatlock of the Ralph L. Wolpert Company, Dayton, Ohio, who furnished the data for the plant a t Crystal Lake, Ill. LITERATURE CITED
Boruff and Buswell. IND.ENG.CHEM.,21, 1181 (1929). Ibid., 22, 931 (1930). Boruff and Buswell, J . Am. Chem. Soc., 56,886 (1934). Buswell, Boruff, and Wiesman, IND.ENG.CHEM.,24, 14-23 (1932). Buswell, et al., Ill. State Water Szirvey BUZZ. 18, 7 (1923). Buswell and LeBosquet, IND. ENG.CHEM.,28, 795 (1936). Buswell and Neave, Ill. State Water Survey Bull. 30 (1930). Buswell, Shive, Bnd Neave, Ibid.,25, 5 (1928). Buswell, Strickhouser, et al., Ibid., 26, 21 (1928). Buswell, White, Symons, et al., Ibid., 29 (1929). Fales, A. A., private communication. Federation of Sewage Works Associations, Comm. sewage works practice, manual No. 1. Johnson, J . Econ. B i d , 9,105-25, 127-63 (1914). . Kimberly, Water Works & Sewerage, 78, 48 (1931). Larson, Boruff, and Buswell, Sewage W o r k s J., 6, 24 (1934). Neave and Buswell,111. State Water Survey Circ. 8 (1930). Neave and Buswell, J . Am. Chem. Soc., 52,3308 (1930). Schlens and Langdon,WuterW o r k s & Sewerage, 88,217-26 (1941). Symons and Buswell, J . Am. Chem. Soc., 55, 2028 (1933). Tarvin and Buswell, Ibid..56, 1751 (1934). RECEIVED January 3, 19.50
SEPARATION OF OIL REFINERY WASTE WATERS ROY F. WESTON The Atlantic Refining Company, Philadelphia 45, Pa.
T h e probleni of oil removal from oil refinery waste waters is discussed herein. The problem includes the separation, collection, and reconditioning of the oil for recharging to refinery processes, and also the treatment of the waste water to make it satisfactory for disposal. Oil is separated from waste water using gravity differential-type separators. The efficiency of this operation is based on the relative contents of that portion of the oil amenable to separation by gravity differential flotation processes. A n analytical procedure to determine “susceptibility to separation” was devised to determine the nonseparable oil content of
a sample. The efficiencies of the various separators used are presented. After the oil is separated it will contain suspended solids and water. These materials may interfere with efficient processing and so it is necessary to treat slop oils prior to recharging to processing equipment. Typical data on the characteristics of slop oil treatment are given. Operatingdata are given for an automatic backwash sand filter installation that is successfully “polishing” a separatoreffluent. Pilot plant studies using biological filters indicate general improvement of separator effluents includingsubstantial reductionsinoil content.
IL originating from leaks, spills, tank drawoffs, processing operations, and maintenance and repair activities may find access t o the plant sewers in almost every part of a refinery. Therefore, the economical and adequate separation of oil from waste water is a problem of considerable importance to the refiner. The problem is that of the separation, collection, and reconditioning of oil for recharging to refinery processes and that of the treatment of the waste water to make it satisfactory for disposal. The treatment of refinery waste waters t o produce effluents of
satisfactory oil content probably will be b u t one phase of the general problem of providing a satisfactory plant effluent. However, it is an important and universally used phase of treatment. Because other aspects of the problems of oil refinery waste disposal have been discussed elsewhere (2-6’) the3e discussions will be confined to the problem of oil removal. I n all known cases, oil is separated from waste water using gravity differential-type separators. During this process oil rises to the surface, sediment settles to the bottom, and relatively small concentrations of oil and suspended solids pass
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