December, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
(4) Gubelmann, Weiland, and Stallmann, U. S. Patent 1,623,949 (April 5, 1927). (5) Hantzscb, Be?., 33, 2528 (1900); 41, 3519 (1908). (6) Hantzsch, Ibid., 38, 2056 (1905). (7) Khorasch, J. Am. C h a . SOC.,54, 674 (1932). (8) Misslin, E., Hela. Chim. Acta, 3, 626-39 (1920). (9) Schoutissen, Rec. trav. chim., 40, 763-74 (1921).
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(10) Sidgwick, “Organio Chemistry of Nitrogen,” Clarendon Press, Oxford, England, 1910. (11) Tassily, Bull. SOC. chim., 27, 19-23 (1920). (12) Taylor, “Reactions and Symbols of Carbon Compounds,” p. 432, Century, 1930. RECEIVED June 13, 1932. The author’s present addresa is 211 First Ave., Oakland City, Ind.
Anaerobic Stabilization of Milk Waste A. M. BUSWELL, C. S. BORUFF,AND C. K. WIESMAN State Water Survey, Urbana, Ill.
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Mixed jlora and a n operating technic have wastes by r e g u l a r a n a e r o b i c HE w a s t e s f r o m milkbeen &cel(,ped f o r the successful ana&robic sewage digestion methods always bottling plants, c r e a m results in failure, because the eries, and cheese factories fermentation and stabilization of milk wastes. waste becomes very rapidly, have, in the past, been found t r o u b l e s o m e a n d difficult to Such treatrt~ntis more economical than Present a condition which, in turn, stops standard methods. It removes 95 per cenf of normal digestion and stahilizahandle. These wastes become sour, very offensive, destroy the the pollut&)n load. Additional treatment on tion of the solids (3, 5, 6). If septic or Imhoff tanks are used a t normal life in streams, and upset filters could be w e d if desired. all, they are built so that the the operation of sewage treatFrom 8.3 to 12.4 cubic feet of gas of a B. t. u. wastes have a detention time of ment plants. This is due mainly t o the fact that they contain a Of about 550 can be recovered at a moderate cost only 24 to 72 hours. The effluents from such tanks, which act high percentage of lactose which f r o m each pound (dry weight) of waste milk mainly as s e t t l i n g basins and solids. This volume and B. t. U . could be inis quickly attacked by bacteria. reduce the p o l l u t i o n load but If these wastes are highly diluted creased by ,Tarburetion. very little, are then treated on with other sewage, they can be filters. handled by regular sewage treatWhittier and Sherman (15’) have investigated the possible ment methods. If, however, they constitute an appreciable part of the flow, they must be treated separately and pref- utilization of whey for the production of propionic acid and ketones. A continuous lactic acid fermentation of whey erably a t the site of the milk plant. Treatment by aerobic oxidation in trickling filters (3.5 has also been successfully worked out by Whittier and Rogers to 6 feet deep) dosed a t rates of from 500,000 to 2,000,000 (12). Buswell and Keave, in some of their unpublished gallons per acre per day (11), sand filters dosed a t about mixed culture studies, were able to recover liquors contain50,000 gallons per acre per day ( 5 ) , or lath filters dosed a t ing as much as 1.7 per cent volatile acids. The gas formed rates of from 250,000 to 2,250,000 gallons per acre per day was composed of carbon dioxide and hydrogen. The combined wastes from milk-collecting and -bottling (79, have been found the most successful. In this connection it should also be stated that filters are efficient only stations usually contain less than 1 per cent solids (3). The when dilute solutions of the waste are being treated (0.05 combined wastes from creameries and cheese factories seldom to 1.0 per cent solids). It has also been found advisable contain as much as 4 per cent solids (3). I n the latter cases, to remove grease and settleable solids prior to dosing (6). the buttermilk and whey wastes could be separated from Filter methods are expensive and no by-product of the the other factory wastes and treated in an undiluted state. treatment is recovered. One treatment plant described by Such segregation is practiced a t plants which recover butterKimberly (b), which was composed of a 10-foot slag filter milk for cattle feed purposes. Owing to its acid condition and a final settling tank, cost $3000, or $116.80 per pound and poor food quality, but little whey is salvaged a t present. of solids treated daily. Another plant using an 8-foot sand Government figures show that there are about 79 million filter cost $1500, or $292 per pound of solids to be treated pounds of buttermilk solids and 339 million pounds of whey daily. Activated sludge treatment has not been found solids thrown to waste yearly in the United States. Over 6.6 million pounds of whey solids are wasted in the state of practicable ($,e). Disposal of milk wastes by broad irrigation at rates of Illinois yearly (IO). (All data in terms of dry weight.) about 6000 gallons per acre per day is utilized by some These figures have been corrected for the amounts recovered plants (4). Such a practice usually produces odors unless for various purposes (buttermilk, 163 million pounds; whey, prechlorination is used. Disposal by dilution, without caus- 18 million pounds). The handling losses may best be suming a nuisance, is impossible for most plants. IBdridge (3) marized by referring to a table compiled by Eldridge (3) states that 2000 gallons of unpolluted water of a high oxygen (Table I). content is necessary for each pound of milk waste (wet weight). TABLE I. MILK-HANDLING LOSSES Chemical precipitation with an acid or alkali, alone or MILK RECEIVED LOSTTO S E W E R accompanied with a heavy metal salt, such as iron or alumiPLANT Min. Av Max num, has been investigated by many (3, 5, 81, including % % % Buswell and Neave of this laboratory (unpublished data). Condensery 0.5 1.5 2.0 0 5 0 8 1.2 Such a method is not practical because it leaves in solution Z e E i i station 0.35 0.5 0.7 1.2 2.0 2.5 the soluble solids (largely lactose) which constitute the major ~ ; ~ a ~ ~ (excluding ~ e e s ewhey) , 6.0 ... portion of the pollution load. There is also left Lhe problem of disposal of the precipitated sludge. Since Boruff and Buswell (1) have been successful in ferEarly studies in this and many other laboratories, as well menting certain sour wastes anaerobically and converting as in large-scale plants, have shown that handling of milk these materials to carbon dioxide and methane, and Neave ,
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CW EMISTRY
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and Uuswell (8) have shown that a large number of the OIganic acids can be fermcnted to t.liese same gases, it seemed probable that the milk waste problem might be solved by this method and a large portion of the solids recovered as power and fuel gas while the residual material was stabilized.
stage tank could serve a number of primary digesters. For the most part the tanks were fed undiluted whey and a mixture of buttermilk and whey waste. Representative analyses of these raw wastes are given in Table IT. Thermophilic studies (53" to 58' C.) as well as mesophilic studies (27to 29" C.) were conducted, but because the former showed no advantage over the latter, only the results of mesophilic J ~ ~ W ~ I M L C N T Al'nucxocar: L studies will be presented. Fermentation and stabilization data covering 8 months Amaerobic fermentation tanks of from 3 Lo 10 liters C ~ S i m i t y vcre fitted with feeding tubes and gas, liquor, and of experimentation are given in Tables I11 and IV. These data are average representative figures takcn frorri expcrimcrital runs of from 35 to 72 days' duration. During this time from 11 to 25 liters of waste were fed to each tank. From these data it is apparent that the undiluted wliey or butterniilk-whey wast,e can be fed to anaerobic fcrmeutation tanlis a t ttie rate of from 2.2 to 2.9 grams of volatile matter per day per liter of tank capacity. From this fermciit.ation there can be recovered 1.6 to 2.4 volumes of gas per day per tank volume. n'o noticeable ainoimt of sludge was fonned in any of the experiments, including one tank that was operated continuously for 208 days. As a result of fermentation, tile overflow liquor from these tanks COW tains only about 3 to 5 per cent of the original volatile solids, and only from 8 to 10 per cent of the organic nitrogen added. The oxygen-consumed (potassium permanganate) values of these overflow liquors show a residual of from 350 t o 460 11. p. m., or a reduction of 98 per cent. The S a y hiochemiCONFLUENCE OF SXALL STREAM POLLUTED wmr D A ~ Y WASTES (LEFT) m n CLEAR EFFLUENTYHOM SEWAGE ea1 oxygen demand of the whey overflow liquor averaged 2425 p. p. m., a reduction of 93 per cent. The overflow from TnEaTmEVT PLAVT (1lhOlfT) the second&age buttermilk-whey tank showed am oxygensludge withdrawal connections. To these tanks were added consumed value of only 150 p. p. m., or an over-all reduction well-digested sevage sludge and asbestos fibers to about of 99.3 per cent. The experiments oil the fermentation of diluted whey one-third the tank volume. The tanks were then filled with settled overflow liquor from an ana6robic s e ~ n g etank. The (I to 1 with water) showed only minor differeiices from those liquor and sludge werc used as the initial medium and source conducted on the concentrated waste. Those on ttie diluted 1 volume of the anaerobic bacteria. The sludge could be largely re- buttermilk-whey mixture (1 volume of wliey 4 volumes of water) show that more grams placed by asbestos fibers which were found to act admirably of buttermilk as the necessary contact material. The particular waste of solids can be fed per day per liter of tank volume if such in question was then fed very slowly. Close checks of the solids are diluted. Greater gas volumes are also recovered (2.7 volumes per day per tank volume as compared wititir pH, volatile acid content, and gas analysis were made r e p lady. If the tank s1ion.t.d a tendency to go sour, the daily 1.9 to 2.4). The most probable explanation of this fact is feedings m r e omitted or reduced for a short time until tho that tlie decomposition of buttermilk, which contains an tank fermented the accumulated acids to carbon dioxide and average of 4355 p. p. m. of total nitrogen, produces concenmethane. In this manner flora were developed which would trations of toxic decomposition products which act as bacrapidly ferinent to carbon dioxide and methane the milk teriostats and reduce the activity of the organisms. High solids added without permitting the acciimdation of organic ammonium carbonate conccntrations are known to be toxic acids. The accumolatioii of acids, with a corresponding de- to some bacteria. At times the ammonia nitrogen concen-
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crease in gas production, was also noted a t times when tanks tration, in tanks being fed buttermiik and whey, ran from were fed beyond their nonnal capacity. The acids in such 1200 to 2500 p. p. m. During such periods low fermentacases were found to be mainly prgpionic and acetic with tive action was a h a y s noted. Dilution of such taiilis with traces of lactic and formic. The greatest concentration of water always reytored normal rapid fermentation. Such lactic ever found was 40 p. p. m. Such an acid condit,ion dilution vas also found necessary in certain othpr studies could he overcome by reducing the feed or by tlie eschmge on thc anatrobic fermentation of casein and peptone. This of liquor between the acid tank and one operating normally. diflirulty was never met in the fermentation of diluted butterA number of studies was conductad in tu.0 tanks which milk-whey mixtures or in the fermentation of whey alone. were operated in series. Rack circulation at such times as Whey contains only about 1352 p. p. m. of total nitrogen. referred to above always reestablished normal fermenta- I n a commercial plant such dilution could be accomplished tion. Such a practice was first used by Horuff and Ruswell by tho addition of all or a part of the wash water. ( 1 ) in the fermenta.tion of beer-slop waste. One small secondThe few experiments on the fermentation of undiluted
December, 1932
IN D U S T R IA L A N D E N G I N E E R I N G C H E MIS TR Y
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TABLE111. ANAEROBICFERMENTATION OF MILK WASTES (At 2 7 O to 29' C.; all data based on continuous feeding experiments in 7- to 10-liter tanks) W H E Y DILD. W I T H EQCAL BUTTERMILK -k W H E Y B U T T E R M I L K AND W H E Y , WHEY 1 TO 1 (UNDILD.) VOL. O F W A T E R W A T E R (1 T O 1 T O 4) Single stage 1st stage 2nd stage 1st stage 2nd stage 1st stage 2nd stage Rate waste fed per day per liter tank volume:o b 30.6 ll 48.5 b Volume (undiluted basis), cc. 34.2 43.5 Total solids, grams 2.4 3.1 2.3 3.5 Volatile solids, grams 2.2 2.9 2.0 3.2 G a s recovered per day per liter tank volume: 1.6 1.9-2.4 0.3 1,: 0.5 2.7 0.7 Volume, liters Weieht. 2.1 2.2-2.8 0.3 1 . l 0.5 3.3 0.7 - erams Gas analyses, %: cot 46.8 39.0 29.0 48.2 27.3 40.4 26.0 CHa 49.8 55.0 61.0 49.6 58.0 58.0 67.0 0.2 0.2 0.2 0.0 H2 0.5 0.5 0.5 2.0 14.5 1.4 7.0 Nz 2.9 5 5 9.5 Volatile matter fed. recovered as gas, 3' % 96 76-97 86-107~ 85 11oc 103 1251 Grams/liter X 0.0624 = lb./cu. it. b Recirculation of 2 to 4 liters daily. Second tank fed oyerflow liquor from first tank. (1) c Includes gas from first stage. Union of water in decomposition reaction accounts for recoveries over 1 0 0 ~ o
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TABLEIV. OVERFLOW LIQUOR,SAKITARY CHEMICAL DATA WHEY
(UIDILD.)
$?latile acids, p. p. m . Total solids, grams/lirer Total solids reduction, Volatile matter, gramdliter Volatile matter reduction. Q Organic nitrogen, p. p. m.' ' Organic nitrogen reduction, % Oxygen consumed, p. p. m. Oxygen consumed reduction, % 5-day b. 0. d p. p. m. 6-day b. 0. d:: reduction, lo
Single stage 7.3 1750 4.7 93.4 2.2 96.6 131 89.9 460 98.1 2425 93
BCTTE;RMILK AND W H E Y ,
1 t o 1 (UNDILD.) 2nd stage 7.4 7.5 1580 1100 6.3 4.5 92.6 93.7 3 .1 3.6 94.6 95.3 262 196 91.7 93.8 150 350
1 s t stage
.98.4 . ..
99.3 .... ....
skim milk that were run did not give as high gas yields and degrees of purification as did the other studies. The tanks did not go sour. Here again the authors feel that the trouble was due to the accumulation of toxic protein decomposition products. There is no reason to believe that diluted skim milk would not ferment readily. Although the sanihry data for the diluted as well as the undiluted waste fermentations (see Table IV) show large percentage reductions in the pollution load, the liquors in most cases should be given additional treatment by adding them to slag, stone, lath, or sand filters, or by diluting by addition to city sewers, where they would ultimately be treated in the city treatment works, or by diluting in a nearby stream, provided sufficient flow is available. Local conditions would determine the practice adopted. As these liquors are not sour (pH 7.0 to 7.5, and volatile acids, as acetic, only 500 to 1850 p. p. m.) nor highly putrescible and contain but little settleable solids, they should not interfere with the normal operations of sewage treatment works.
COSTOF EQUIPMENT AND INSTALLATICIX Assuming that anaerobic digestion tanks can be built for 50 cents per cubic foot and figuring 12 per cent for interest, amortization, and repairs, such tanks cost 16.4 cents per thousand cubic feet of rolume per day. On the basis that raw, unsettled, and untreated buttermilk and whey wastes can be fed a t rates of from one twentieth to one t>hirtieththe fermentation tank volume per day (2.3 to 3.6 grams per liter) and produce 1.6 to 2.7 volumes of gas per day per tank volume, gas could be produced a t costs ranging from 6.1 to 10.3 cents per thousand cubic feet. -4s compared with other methods of gas production or transportation, this is a moderate cost. The B. t. u. of the fermentation gases average about 550. This B. t. u. and the total volume could be readily increased by carburetion through gasoline. A volume of 776 liters of fermentation gas, when bubbled through Phillips 66 gasoline a t room temperatures, was found to be increased in volume to 840 liters with an increase in the B. t. u. to about 990. This was accomplished by the vaporization of 382 cc. of the original 700 cc. of gasoline added. On the basis of an average feeding of one twenty-fifth of
WHEY
DILD. WITH EQUAL
VOL. OF WATER 1st stage 2nd stage 7.0 7 2 1690. 500.3.6 3.4 95.2 95.4 1.5 1.2 97.8 98.2 103 110 92.0 91.5 695 570 97.0 97.5 5500 2900 85.6 92.2
RUTTERMILK
mHEY
+
WATER(1 TO 1 TO 4) 1st stage 2nd stage 7.0
1850
3.5 95.1
2.3 96.6 153 94.5 500 98.1 4250 91.8
7.4
506 3.4 ~
95.2 2.2
96.8 17 1 94.0 380 98.6 2620 94.7
SKIM AfILK (UNDILD.)
Single stage
16.7 1.8 1.7 1 0 1.2
41.3 55.2 0.6 2.9
71
SKIM (UNDILD.) RIILK Single stage 7.5 1265 5.3 95.2 3.1 97.0 361 94.0 890 97.4 4650 91.7
a volume of milk waste (undiluted basis) per day per tank volume, it would require a tank, or tanks if operated as a two-stage 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 a t 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 817.46 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. Thus the total treatment plant cost of anaerobic fermentation followed by aerobic filtration is only a small percentage of that reported ( 5 ) for the treatment of milk wastes by standard present-day methods, which, incidentally, are merely treatment methods and give no valuable by-product. Anaerobic fermentation of milk wastes followed by secondary treatment-namely, filtration-will not only give efficient stabilization but will also produce 8.3 to 12.4 cubic feet of gas per pound of dry solids added. LITERATURE CITED (1) Boruff and Buswell, IND.ESG. CHEM.,24, 33 (1932). (2) Buswell and Boruff, Sewage Works J.,4, 454 (1932). (3) Eldridge, Mich. Eng. Expt. Sta., Bull. 36 (1931). (4) Gascoigne, Sewage Works J.,3, 44 (1931). ( 5 ) Kimberly, Water Works and Sewerage, 78, 48 (1931). (6) Levine, Sewage Works J., 4, 322 (1932). (7) Levine et al., Iowa State College Ens. Expt. Sta., Bull. 81 (1926). (8) Keave and Buswell, J. Am. Chem. Soc., 52, 3308 (1930). (9) Steel and Zeller, Texas Eng. Expt. Sta., Bull. 38 (1930). (10) U. S.Dept. .4gr., Dept. of Agr. Economics Repts., Sept., 1931. (11) Walker, Sewage Works J., 2, 123 (1930). (12) Whittier and Rogers, IND.ENG. CHEM.,23, 532 (1931). (13) Whittier and Sherman, Ibid., 15, 729 (1923). RECEIVED June 13, 1932.
