Augued IB52
Industrial Wastes A simple treatment of dairy wastes produces. a high protein sludge containing vitamin Blz bg Harold R. Murdock
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JULY 1951 this column discussed the wastes from milk processing plants and referred particularly to the splendid textbook by W i t t i e r and Webb (6),staff members of the Agricultural Research Administration. Now from this same organization another group of scientists report an important research directed to the treatment of the dilute waste waters from the milk industry (1); As is often the case in well planned research, these scientists, particularly Hoover et al. (g), have not only found a practical disposal method for very dilute milk wastes but in addition have proved that the sludge produced from the aeration method contains 65% protein and a vitamin Blz content almost twice that of commercial feed supplement. Then, not content with this accomplishment they suggest their process as applicable to many other organic wastes and report finding vitamin BIZ in the activated sludge from a sewage plant ( 3 ); this indicates the potential importance of sewage sludge as a valuable anlmal feed substance. The dilute waste waters from a milk processing plant come from many sources, such as the washing of cans, coolers, bottling machines, and pumps. Leakage, spilling, and occasional overflowing of tanks and bottles also add to the dilute waste. Losses of around 1% of the total milk processed are considered reasonable normal operation losses in a well-managed milk processing plant. Small milk plants handle about 10,000 pounds of milk per day. Many plants process ten times that amount. The larger plants, which are increasing in number, receive over 500,000 pounds of raw milk each day. Because of the dilution of the wasted milk, the effluent going to the stream contains between 0.1 and 0.2% milk solids. Such solutions have a B.O.D. value between 800 and 1600 p.p.m. Domestic sewage has a B.O.D. averaging 200 p.p.m. Hoover and his associates report a survey of an integrated milk processing plant that processed 435,000 pounds of milk daily by separating the cream, condensing the skimmed N
August
1952
milk, and manufacturing ice-cream mixes. Under careful operations, they report t h s t the dilute waste averaged 133,000 gallons a day and carried a B.O.D. of 1400 p.p.m., which is equivalent to the domestic sewage from 8750 people. Milk contains about 5% lactose, 4% protein, and 3% fat, according to Hoover. The whey remaining after cheese production contains all the lactose and about one fourth the proteins originally present in the milk. Consequently, one half the total milk solids is in the whey by-product. Utilization of whey in the manufacture of food products and other industrial applications is increasing (4,6). A 1951 survey of the U. S. dairy industry indicates that 14.2 billion pounds of whey was produced from milk processing. This production may be classified into the following categories : (1) whey now utilized which amounts to 5.4 billion pounds; (2) whey still available economically but awaiting utilization aggregates 3.0 billion pounds; (3) whey production considered unavailable for practical utilization, because it is produced in plants where the cost of transportation to a central processing plant would be greater than the commercial value, amounts to the balance, 5.8 billion pounds. Many small cheese plants in which one half the milk solids must be considered an industrial waste have a tangible problem awaiting solution. During 1951, according to Hoover et al., over 100 dairy plants in Pennsylvania were under legal action to treat their waste waters or close down. For such reasons the U. S. Department of Agriculture was called upon to find a practical answer. There were already many treatment plants in various localities processing milk wastes successfully from a technical viewpoint, but these units were expensive in both plant cost and operation. What was needed was a simple process, requiring modest expenditure for the treatment plant, which could be used by small cheese plants as well as large milk processing plants. The project was assigned to the Bureau of Agricultural
and Industrial Chemistry, Agricultural Research Administration , and Hooper, Porges, and staff were authorized to make the scientific study. Because of simplicity, the use of air to oxidize the dilute milk wastes was given prime consideration although direct aeration processes had not been found satisfactory in early trials. B.O.D. reduction amounted to only Soyo in 12 hours and failure to obtain greater reduction by more prolonged aeration was puzzling. In these studies it was noted that aeration produced acidity which virtually stopped oxidation. It was then decided to study the ability of various bacteria organisms to assist oxidation by aeration. A rapid analytical method to measure the rate of oxidation changes was essential. The fairly homogeneous character of dairy waste which contained only two major chemical components-lactose and protein-made the application of a chemical in evaluating oxygen demand logical. An excellent method was adopted using potassium dichromate as a chemical oxidant. Comparison of the chemical method with the standard B.O.D. method showed the chemical oxygen demand (C.O.D.) to be practically equivalent to the 20day B.O.D. tests. By applying the usual factor of 68%, the standard &day B.O.D. values were checked rather closely. Using this control method a study of the aerobic oxidation in the presence of soil organisms, on a solution containing 0.17, skim milk solids, was made. Confirmation of earlier experimenters that a reduction of 5070 B.O.D. was readily achieved was proved. But the change in the nature of the material was distinctively different. The lactose and protein, instead of being converted to other soluble products which still had a B.O.D. value, had gone through a different metamorphic change. The bacteria organisms had consumed these soluble (Continued on p a g i i 0 0 A )
INDUSTRIAL AND ENGINEERING CHEMISTRY
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c O N C E N T RATE D ~ S U L P H U R I C ACID is best handled by vertical I type pumps especially built for this purpose of cast iron and steel. For i h a n d l i n g 20% FIG. Oleum same type 19.447 of Vertical Pump is successfully used when made of steel. “Mixed Acids” have been handled very successfully with steel vertical type , pumps. Taber Vertical Design eliminates all stuffing Box Leakage because Stuffing Box is located above liquid level. Bearings are of liberal dimension so as to increase duration of performance. These pumps are also built of special alloys when such alloys are obtainable and approved by National Production Authoritv. whose approval is required, and determined by END USE of product manufactured. Therefore, if you have need for special alloy pumps, be sure to state the END Please use your business USE. stationery when writing for this BULLETIN V-837. TABER P U M P COO(Est. 1859) 293 Elm St., Buffalo 3, N. Y. -
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chemicals and formed insoluble cell tissues which when filtered from the waste water, gave a filtrate of negligible B.O.D. value. Measurement of the rate and extent of synthesis of bacteiial cells showed that 1000 p.p.m. of milk solids was completely assimilated by the organisms in 5 to 6 hours. Further oxidation of these cells by their own metabolism required 30 to 40 hours longer. During the rapid reaction us much as 0.4 p.p.m. oxygen was consumed each minute. When oxygen was not supplied fast enough to meet this rate, the system becamemaerobic and organic acids were formed; these reduced pH and destroyed the activity of the bacteria organisms. Two processes have now been proposed t o the milk industry, each of which should meet the requirements of a plant depending on its local situation. The partial treatment process is possibly the most economical and flexible in application, whereas the complete treatment process separates the bacterial sludge from the waste and consequently gives a very low B.O.D. value. One or more treatment tanks and means for bubbling air through the dilute milk waste are the only equipment requirements in the partial treatment method. I n the early morning hours before the wastes from a receiving station or bottling plant are being produced in greatest quantity, the treatment tanks are emptied except for one fifth of the solution which represents the treatment of the previous day. This serves as a culture medium for treating the next batch. During the 4 to 6 hours in the morning bottling operation, the dilute waste produced is pumped directly into the treatment tanks which are aerated continuously during the entire 24-hour day. The rapid growth reaction is completed within the filling period and the autoxidation of the cells in order to maintain themselves continues until the tanks are drained to the receiving stream again during the early morning hours, with the exception of that amount retained as a cultuie medium for the following day. The effluent t o the stream consists of a well-aerated dilute suspension of bacterial cells. A reduction of 50% in total solids will be obtained and the 5-day B.O.D. of the waste reduced about 759” since the cells are relatively stable toward further
oxidation. Because the effluent is discharged during the night, this may be acceptable waste for a sanitary sewage plant in many places since such operations are not usually a t normal operation rates during early morning hours, Iri the complete treatment method the same equipment and processing are used, but the bacterial cells produced ale removed. This results in a 95y0 ieinoval of 5-day B.O.D. from the treated milk waste. The separation of the cells from the solution has been proved feasible by the use of centrifuges. Although small plants would not produce more than 10 pounds of dry bacterial cells per day, larger plants mould have a more imposing problem in their disposition of 200 to 500 pounds per day. Analysis of such sludges shows a protein content of 65%. This fact encouraged Hoover and Porges t o consider the use of sludge as animal feed. Analysis showed 3.3 mg. of vitamin BIZper pound of dry sludge as compared t o a value of 1.5 mg. per pound for commercial feed supplement (3). Inspired by this richer vitamin source, Hoover tested aerated sludge from municipal sewage treatment plants and obtained values similar to those found for dairy wastes. This extension of their research is still proceeding in laboratory ahd chick feeding tests conducted a t the U. S. Department of Agriculture, Animal Industry Labomtories, Beltsville, Md. I n the meantime, a pilot plant for treating 10,000 gallons a day of dilute milk waste from an operating dairy in Pennsylvania has been constructed in which all operating variables will be under control. The plant will be in operation in September 1952. From thesedata thedairy industry canlookforward to a sound program which promises to remove the dairy industry from the list of grievous industrial pollution problems. Literature cBted (1) Hoover, S. R., et al.,
Science, 114, 213
(rlug. 24, 1951).
(2) Hoover, S. R., et. al., Sewage and I n d . Wastes, 23, 167 (February 1951). (3) Ibid., 24, 38 (January 1952). (4) Xastens, M. L., and Baldauski, F. A . , IND ENG.CHEM.,44, 1257 (1952). (5) Whittier and Webb, “By-Products from Milk,” Washington, D. C., U. S. Dept. of Agriculture f.1950). Correspondence concerning this column will be forwarded promptly if addressed to the author, YoEditor, INDUSTRIAL A N D ENQINEERING CHEMISTRY, ll55-16th St , N.W , Washington 6, D. C .
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 44, No. 8
