Liquid Industrial Wastes tion equivalents daily in 1944 t o a present average daily loading of 28,000 population equivalents, a reduction of 92%. Of the present total loading, an average of 20,000 daily population equivalents is being disposed of t o t h e Hammond Sanitary District treatment plant, A substantial part of this load t o Hammond is bone char wash water and steep water condensate. A plant improvement program t h a t is now well under way should reduce this load by 40%. In effecting the aforementioned 92% reduction in t h e industrial waste loading, t h e company has instituted control measures t o eliminate the human factor as much as possible, and thereby ensure normal steady control with better than average freedom from accidental shock loads. All possible avenues of trade wastes have been thoroughly surveyed and are under constant surveillance. The present setup for the disposition of the eflluent from t h e plant is illustrated by Figures 3,4,and 5.
of solids materials normally considered waste, and not by elaborate pretreatment or sanitary disposal techniques. American Maize has incurred direct benefits from this program in t h a t the company now experiences a 1% increase in over-all plant yields over what was once thought normal. Figured a t t h e present cost of corn this is roughly worth $175,000 a year. Of course the company has exceeded the dictates of the law of diminishing returns to obtain this yield increase but it does help t o support the overhead imposed by the over-all program. T h e company has had t o carefully control all phases of production planning t o make the waste abatement program work and this has proved a hidden asset, in t h a t all plant operations now run more smoothly and are under more uniform control. T h e general production worker has been well informed as t o the part he plays in waste abatement. H e has developed a genuine interest and the results are improved morale and closer operation control.
Acknowledgment
Conclusion To accomplish this appreciable reduction in trade wastes, the company has invested roughly $850,000. It has replaced equipment, which under normal conditions still possessed years of usefulness, and it has injected practices into the normal manufacturing processes, which at one time would have been considered hazardous t o h a 1 product quality. But, in general, it has accomplished its reduction in trade waste by the elimination and saving
The company has cooperated t o the fullest extent possible with the Hammond Sanitary District on the mutual problems and the company is deeply indebted t o Carl B. Carpenter, superintendent of the Hammond disposal plant for his sincere cooperation and help in solving a problem t h a t would have otherwise been far more difficult. RECEIVBID for review September 6, 1951.
ACCEPTEDJanuary 12, 1952.
DAIRY INDUSTRY H. G. HARDING, NatZond Dairg Research Laborator~es, Inc., Oakdale, Long Island, N. Y.
Since reduction of biochemical oxygen demand in dairy waste waters by waste prevention and waste saving is much more economical than subsequent waste treatment, much progress in this direction has been made by the dairy industry. Any of the well-known waste disposal processes used for city wastes can be used successfully for dairy wastes, but may easily become too costly as this industry has a low margin of profit. Therefore, a continuing search is under way for reliable, low cost, modified treatment
methods. Combined treatment with city wastes, where adequate capacity and an equitable cost distribution agreement can be obtained, is preferable to separate treatment. In small dairy plants, aerated flow equalization may provide sufficient treatment or a valuable pretreatment. The trend in thedairyindustryistousevariousmodifications of standard biochemical oxidation treatments in trickle filters or activated sludge systems. A satisfactory and economical method of excess sludge disposal is still lacking.
T
higher milk volume during the spring and summer months than during the winter months; and the extremely rigid and sometimes contradictory state and municipal sanitary codes, which frequently do not permit the very things that would be most helpful in reducing plant losses. For instance, the exacting sanitary requirements make it necessary to take all equipment apart for cleaning every day. It was also pointed out t h a t the trend in the dairy industry is toward large manufacturing plants fully equipped to handle all by-products, although there still are a t present a large number of widely scattered small plants incompletely equipped t o handle by-products. The establishment of more large by-product plants which utilize all available waste products from nearby small plants will do much to reduce stream pollution. The industry was also marked by extreme efforts toward waste saving and waste utilization within the dairy plants. Another trend was toward the segregation of cooling waters for discharge t o rivers or storm sewers or for recirculation over cooling towers, and segregation of domestic wastes for treatment in septic tanks or
H E waste disposal problem of the dairy industry as it appeared in 1947 was reviewed (16)at the Industrial Wastes Symposium held during the spring meeting of the AMERICAN CHEMICAL SOCIETYt h a t year. Some of the features of the industry t h a t make the waste problem particularly difficult were discussed. These were and still are the great variety of products made, all producing wastes of different strength and composition; the extremely wide distribution of both the sources of raw materials-namely, the more than 4 million dairy farms in this country and the still more widely distributed ultimate consumers, which are the entire population of the country; the high nutritional value of dairy products, which is their greatest asset as a food and is also their greatest drawback from the point of view of pollution; the perishable nature of the products, which makes it necessary to avoid all possible delay in processing which might be caused by power failures or breakdown of processing or transportation equipment; the highly seasonal character of the industry which makes it necessary to provide a great deal of expensive extra equipment and extra labor to handle the 50%
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L i q u i d Industrial Wastedisposal to city sewers. The combined treatment of dairy waste with city waste wherever a mutually satisfactory agreement could be reached about treatment costs was a tendency of the industry, also.
These 1947 trends in the dairy industry are continuing today and are gaining momentum, as are also the trends in the whole country toward more and better elimination of stream pollution.
Segregation of Plant Waste Waters I t is desirable to segregate the various liquid wastes in the dairy plant for separate treatment or disposal. These nastes include domestic wastes; uncontaminated cooling waters; spoiled or excess products; drips, leaks, and first rinses; and wash v-aters from containers and equipment. Domestic wastes from washrooms and toilets should be discharged directly to cit'y sen-ers or to separate septic tanks. The effluent from these tanks should discharge preferably to leaching pits or underground drain fields but can also be treated in conjunction with dairy a-aste. Uncontaminated cooling waters should be segregated and reused wherever economically practical or discharged to storm sewers or directly to the stream. I n nearly all cases where dairy product evaporators are properly operated and equipped with adequate entrainment separators, the condenser Jvaters will be YO low in organic content that they can be discharged directly to the stream. In some cases it .il.ill be desirable to recirculate the condenser water through a spray tower for re-use. The small volume of overflow from the tower and, at the end of the day, the tower water itself should be treated, together with the floor waste. This appears to be particularly desirable for condenser waters from the concentration of fermented products containing volatile alcohols, acids, and other compounds. Spoiled or excess products, such as skim milk, buttermilk, or whey, should be utilized and not dumped down the drain or into streams. Wkere a sufficient volume of these products is available, i t is economical to concentrate and even to dry them for feed. Thus one specialized by-products plant may process the excess by-products from a number of nearby dairy plants. In other cases the fluid by-products may be disposed of directly to the farmers for animal feed. I n exceptional cases it may be necessary to dump excess by-product's on isolated land. Relatively small volumee of skim milk and whey are being converted into chemurgic products, such as casein, lactalbumin, lactose, lactic acid and lactates, alcohol and butyl alcohol. Unfortunately, these transformations may be accompanied with increased losses of organic matter in the plant waste waters for the individual plant, even if the total loss of whey for the particular territory is reduced by more complete utilization of the whey. Drips, leaks, and first rinses from milk processing equipment should be saved and utilized or disposed of ot'herwise than in the plant drains. It should be possible to reprocess product-saving first rinses, which are collected in a sanitary manner. In other cases these should be utilized for animal feed. In certain situations i t appears practical to plug the floor drains temporarily and operate with a dry floor during processing. At the end of processing, any product drip or splash which reaches the floor is rinsed to the floor drain receptacle and removed for animal feed. Wash waters from containers and equipment will go directly to the floor, if the above segregations have been made, and will contain practically all of the organic matter contributed by the dairy plant. Since strongly allcaline cleaners are used, the p H of the floor wastes tends to be slightly but not excessively alkaline. This is due to the dilution and buffering effects of the large volumes of rinse water, to the buffering effect of milk solids, to the use of low concentrations of more effective alkaline cleaning compounds, and to the use of acid-type cleaning compounds for certain cleaning operations. Where strong caustic solutions are used for cleaning, as in soaker-type bottle washers or vacuum evaporators, the effect 488
on the pH of the waste treatment plant waters on the receiving stream can be minimized by providing for the re-use of the caustic solution after settling or for the equalization of its discharge over a considerable period of time. The dairy industry has been made aware of the importance of by-products utilization, waste prevention, and waste saving by the activities of various state control agencies and by various industry groups, such as the Task Committee on Dairy Wade Disposal of the Dairy Industry Committee ( 1 4 ) and the Dairy Engineers Committ'ee of the Pennsylvania Association of Milk Dealers ( 2 ) . As a result there is a continuiiig trend toward lower waste losses associated with various dairy processing operations. Undoubtedly there is an irreducible mininiuni loss associated with each processing step, but, as improvements in equipment, supervision, and employee education continue, losses will be lowered. For instance, in a receiving station where the standard loss based on 1947 standards (a)would be 9 pounds of 5-day biochemical oxygen demand per 10,000 pouiide of milk received, cooled, and loaded into tank trucks, it was possible in 1951 to operate for 6 consecubive days with losses of less than 1.4 pounds of biochemical oxygen demand per 10,000 pounds of milk received. However, to do this it vias necessary to modify the can washer, to collect product-saving prerinses from cans and equipment, to plug the floor drains during the receiving period, and to have very good cooperation of the plant manager and employees.
Combined Dairy and City Wastes It is now generally agreed that dairy waste can be treated successfully with any of the well-known chemical or biological treatment processes used for city sewage. Milk waste, because it contains easily digestible organic materials, is perhaps more amenable to standard biological treatment processes than city waste. Where the treatment unit has sufficient capacity to handle the maximum load, adequate precautions are taken t,o alleviate unfavorable conditions, t,he troubles of city waste disposal plants handling milk waste tend to disappear ( 1 ) . Invariably these troubles have been caused by the occasional dumping of large amounts of excess by-products, such as whey or skim milk, and the troubles have been eliminated as soon as the overloading stopped. In city plants with only primary treatment, such as Imhoff tanks, little or no reduction can be expected in the soluble biochemical oxygen demand contributed by the milk sugar. If good biochemical oxygen demand reduction is required, then the dairy waste should be pretreated with a recirculating trickle filter or an aeration tank, and the city disposal plant can then act as an efficient final settling tank and sludge disposal unit for the dairy waste treatment unit. In cases where the city has complete treatment facilities, a pretreatment of the dairy waste is usuallj- not economical. It should definitely be cheaper and better to build and operate one treatment unit than tv-o or more. And there is a groLving realization by municipalities that they should, t o the best of t,heir ability, assist in treating the wastes from the industries on which the town bases its prosperity and a large part of its tax income.
Separate Treatment Plants The treatment methods which are used for city wastes and which can be used for dairy wastes include a wide variety of scptic t,anks or digesters, broad irrigation, chemical precipitation, trickle filters, axid numerous activated sludge-type processes. Septic tanks or anaerobic digesters, while very successful on a small scale under carefully controlled conditions ( I S ) , have not given consistently good results under plant conditions. The reason may be that temperature and agitation have not been as carefully controlled as necessary. Indications are that temperatures of 90" to 103" F. lvith just sufficient,agitation to prevent a
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L i q u i d Industrial Wastes solid scum layer are required for best results. Then a 50% reduction in biochemical oxygen demand can be expected with 3 days’ retention and 80% reduction with 10 days’ retention. However, if a tank is overloaded it becomes acid and ineffective, and then is difficult t o get back into proper condition again. Broad irrigation is reported t o be satisfactory on sandy soil in warm climates and where flies and odors will not cause trouble. If this treatment method is used, cooling waters are not segregated from the floor wastes. Chemical precipitation of milk proteins and other suspended matter with either aluminum or iron salts can give crystal-clear effluents which still may contain soluble lactose with considerable biochemical oxygen demand. The lactose can be removed by yeast fermentation (activated sludge) before chemical precipitation, but this is a cumbersome process. The chemicals are expensive, the sludge is voluminous and difficult t o dispose of, and so these methods are not widely used. Besides, if activated sludge is used, results are already so good that i t is not necessary to use chemical precipitation. For twenty years nearly all investigators have agreed t h a t the treatment of milk waste on trickle filters is the most practical method of milk waste disposal, and it is undoubtedly correct that trickle filters will do a good job if properly constructed and operated. The trend has been toward the use of recirculating, relatively shallow (3.5- t o 6-foot deep) trickle filters with very coarsemedium (3- to 3.5-inch size), wide-open underdrains, high rates of flow (20 to 30 million gallons per acre per day or more), and high ratios of recirculation to raw influent flow-for instance, 5 t o 1 to 10 to 1 or higher. The tendency has been to provide sufficient raw storage capacity t o obtain reasonably good equalization of flow and biochemical oxygen demand loading over the 24 hours. Severtheless, several high load units operate very successfully without much equalization, and therefore it appears possible t h a t with high recirculation ratios it may be just as economical to take the waste as it comes, particularly since the high recirculation ratios themselves tend t o have a marked load-equalizing effect. The permissible loading on milk waste trickle filters does not appear to have any particular limit, but if a consistently good effluent, for instance, under 30 p.p.m. biochemical oxygen demand, is t o be obtained, then the average 24-hour loading must not exceed 1pound of biochemical oxygen demand per cubic yard. With complete equalization of both flow and organic loading, it is possible to double this loading. Operating results have been good. Biochemical oxygen demand reductions of 90 t o 97y0 have been observed on repeated surveys on four high-rate, two-stage recirculating trickle filters with two-stage split clarifiers ( 1 7 ) . However, there is no definite proof that two stage is better than single stage. By the use of concentric trickle filters and split clarifiers, i t is possible t o build two-stage units for very little more money than single stage, and it seems logical to assume that they should be able to produce better effluents and give a somewhat greater margin of safety against shock loads caused by accidental waste of milk in the plant. Tricklers which are built overground with wire mesh sides have a low cost of construction but are not suited for winter operation in cold climates. Overground construction is economical in many cases, but the tricklers must he shielded as much as possible. The question of clarification has been very much discussed. The trend is to provide a clarifier that gives a t least 1 hour of actual retention for the part of the effluent t h a t is discharged as final effluent and to provide reduced or no clarification for the part of the effluent that is recirculated. Several large installations have been equipped with mechanical clarifiers and automatic sludge removal, but most of the new installations have simple settling tanks with hopper-shaped bottoms. These are cheap but have well-known shortcomings. For example, sludge tends to cling
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to the hopper walls, become septic, and then float to the top and form a scum layer that may cause odors. The use of duplicate pumps is undoubtedly a step toward more reliable operation. Regular commercial rotary distributors are relatively very expensive for small trickle filters but are reliable. For the control of recirculation, the trend appears toward the use of float-controlled butterfly valves rather than regular float valves or split weirs. In some plants both split weirs and floatcontrolled butterfly valves are used, the f i s t to ensure a certain proportionate recirculation a t all times, the other t o ensure full 24-hour operation by recirculating all effluent when the level in the equalizing tank is low.
Activated Sladge Processes There has been a feeling in the dairy industry that construction costs of trickle filters are too high in proportion to the cost of the milk plants themselves and that some cheaper treatment method must be found if pollution elimination is going t o make rapid progress. Also, a more flexible treatment method would be desirable t o handle the relatively short flush season volume of milk. Several installations of the activated sludge type have been made in an effort t o see if this would not give R more economical answer t o the dairy waste disposal problem. It seemed that with milk wastes i t might be possible t o get satisfactory effluents without the fairly complicated sludge concentration control methods now employed in city waste disposal plants which use activated sludge. Experience a t Belle Center, Ohio, with such a system but with careful sludge control has been reported in the literature ( 8 ) . Results have been very good. Raw waste with a biochemical oxygen demand of about 1000 p.p,m. is treated with about 3600 cubic feet of air per pound of biochemical oxygen demand and yields a final clarified effluent with less than 10 p.p.m. of biochemical oxygen demand. At Springdale, Conn., there is a simplified dairy waste treatment plant using modified activated sludge in connection with a milk bottling plant. Since this was the &st treatment unit of its kind, it has undergone various modifications as experience JTas gained in its operation. The flow sheet for this plant a t the present time is as follows:
Floor wastes first pass through combined sand trap, grease trap, screen chamber, and weir tank equipped with an automatic sampler. The wastes then pass on into an underground pump pit with two float-controlled submerged sump pumps. This provides only partial flow equalization. The waste is pumped into an overhead weir tank for regulation of flow into the aeration system. Excess flow returns to the flow equalization tank. The regulated raw flow, together with a float-controlled make-up from the aeration tank, is pumped through three jet eductors into the lower portion of the overground, vertical, cylindrical aeration tank of 15,000-gallon capacity. Blower-supplied air is mixed with the waste in the jets and rises in the aeration tank. The aeration tank overflows to a cylindrical settling tank or clarifier with a motor-driven spiral rubber scraper for bringing the sludge to a central discharge chamber from which it is normally pumped back into the aeration system for recirculation. Excess sludge may be discharged to an underground digester which overflows to the pump pit. The clear effluent from the clarifier passes through an effluent weir tank, equipped with an automatie sampler, and on to the outfall in the creek. At times of low raw flow, a float-controlled butterfly valve returns effluent t o the pump pit for 100% recirculation. For more than a year, this system has operated with no reported upsets and with very satisfactory results. The raw waste has shown 800 to 1200 p.p.m. biochemical oxygen demand and the effluent about 8 to 30 p.p.m. biochemical oxygen demand. Onehour settled sludge volumes have varied from 40 to more than 90%. Air has been supplied a t the rate of about 500 to 800 cubic feet per pound biochemlcal oxygen demand. At times there has been considerable excess sludge and a t other times the system has been reportedly operated for as long as 3 months with no sludge discharge. Since the aeration tank and exposed lines were insu-
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Liquid IndustiGal W a o r e s lated, this system has operated continuously, and the temperatule in the system dropped to only about 72" F. nhen the outside temperature mas about 10" F. below zero. At times the sludge floc appeared to be easilv bioken up and the liquid pump pressure on the jets had to be greatly reduced. Rarely has it been necessary to use aluminum salts to get satisfactory settling in the clarifier, which gives a retention time of 3 hours or more. The average retention time in the aeration tank is about 28 to 40 hours. There are more than a dozen other new plants of this same general type of activated sludge treatment which have been installed in the past three years (3). Some of them are so-called minimum treatment units (6, Y ) , which are barely t h a t since they lack effective clarification of the effluent Others have been installed in conjunction with other treatment units and have helped greatly in handling increased raw loads. One interesting installation a t a country manufacturing plant has five vertical aeration tanks which operate in parallel. During the flush season, all five tanks are used, while duiing the period of minimum milk intake in the fall and winter, only two or three aeration tanks are operated. This makes it possible to reduce operating costs during the slack season. For efficient atilization of the air, fairly fine bubbles are deemed necessary. However, in dairy waste, diffuser plates, saranwound diffuser tubes, and pipes with drilled orifices or special nozzles have all shown a much greater tendency t o clog and so build up excessive air pressure on the blowers than is reported in city waste. These devices have frequently had t o be cleaned a t least weekly and often every two days, which has added t o the cost of operation. However, it has just been reported that by the introduction of moisture from steam into the air going t o the diffusers, one set of diffuser tubes has been maintained in continuous operation for more than five TTeeks, whereas formerly, without the steam, they had to be replaced about twice a week. This moisture is supposed to prevent the drying out of aeration tank liquor which gets inside the diffuser during installation or during power failure. Unfortunately, power failures occur all too frequently in some country plants. Jet eductors vhen properly protected with screens on the inlet have given very little trouble. It is reported that the impingement jet diffusers were tried in two dairy waste aeration systems but, after a short time, were replaced with other types of diffusers.
Sludge Disposal The problem of practical handling of sludge from milk waste trickle filters or activated sludge-type treatment plants has not been solved. There is still no satisfactory information available on the amount of sludge or t h e amount of biochemical oxygen demand in the sludge t o be expected from these milk waste treatment plants. However, recent work on the aeration of skim milk waste at t h e Eastern Regional Research Laboratory by Hoover and his associates (4,5, 9-11) indicates t h a t about 50 t o 60% of the raw biochemical oxygen demand is transformed into protoplasm and only 40 to 50% is really oxidized. It should be pointed out t h a t the ratio of air t o liquid in this work has been about 30 times t h a t used in milk waste aeration treatment plants. However, this may have no significance. Assuming t h a t the chemical oxygen demand results are proportional t o t h e biochemiical oxygen demand, then the excess sludge from aeration treatment of dairy waste would contain a t least 50% of the influent biochemical oxygen demand. Presumably similar amounts of sludge would be obtained from trickle filters. I n some plants the sludge is hauled away in tank trucks and dumped. In other plants the sludge is discharged t o sand beds or digesters. I n a few plants sand beds have been provided to take care of the humus from the digesters. I n practice, digesters do not seem t o be very reliable, probably because of lack of temperature control. It may well be t h a t under most conditions it is more practical to send the sludge directly to sand beds and eliminate the digesters. Unheated digesters are frequently used
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but are not satisfactory, even nhen their capacity is ample on the basis of the usual city waste design figures. The trouble has been that scum and sludge have rapidly accumulated and so reduced the capacity of the digwter. It, seems necessary t o provide for temperature control and for agitation for keeping bhe scum down. Where this has been done, it is reported possible to kcep a digester in operation of milk waste sludge for more than three years with no reported withdrawal of humus or discharge of excessive solids through the effluent. In regard to the transfer of sludge from the clarifier to the digester, various types of continuous or intermittent gravity discharge arrangements have been tried unsuccessfully. However, air lifts have been used satisfactorily a t several locations. The air for the lift is applied from a small compressor, vhich is operated for a few minutes every half hour by an electric timer. I n most cases the effluent from the digester is returned t o t h e raw waste pit.
Waste Sampling and Testing Dairy waste varies greatly in volume and strengt,h during the day, and in order t o find out, the strength and volume of the raw waste and of the effluent from dairy waste treatment plants, this laboratory has developed an automatic sampler (15),which collects samples a t regular intervals directly in proportion t o the flow over the weir. This gives a composite sample whose volume is directly proportional to the total flow. These samplers have been of considerable benefit in waste survey work. I n fact, one group of plants has obtained 30 of these samplers for the daily sampling of raw and treated waste in all plants. Although the &day biochemical oxygen demand test is standard for the determination of the strength of milk waste, there is a need for a quick test for estimating the strength so as to follow operations more closely. For this purpose, the Rhame dichromate-phosphoric acid-sulfuric acid test (12) as modified by Eldridge (10) is being used more and more. With this test, results are available within an hour. Although results with this test on samples of diluted milk show good correlation with the ultimate biochemical oxygen demand, the results on samples of raw and treated milk waste do not always show a systematic relation t o the 5-day biochemical oxygen demand. Whether this is due to inadequacies in the biochemical oxygen demand test, in the chemical oxygen demand test, or both, is not, known. Nevertheless, the chemical oxygen demand test appears t o offer the best quick Bontrol test now available for milk wastes.
Plow Equalization rnnd Aeration Since the object of waste treatment is to prevent stream pollution, it appears that the real measure of the pollution effect of a given wast,e would be the maximum number of pounds of biochemical oxygen demand per hour discharged t o the st'ream rather than pounds biochemical oxygen demand per day or per any other larger time unit.. Streams have considerable ability t o handle soluble biochemical oxygen demand by dilution and re-aeration. This is recognized by some states in that milk plants below a certain size are excused from waste treatment, Since there are many small receiving stations which operate only five t o six hours a day, the installation of a large waste storage tank for flow equalization is desirable. *4pump raises the waste to a flow-regulating weir box, and the return of excess flow from the n-eir box to a splash plate in the tank keeps the waste fresh and promotes reduction in biochemical oxygen demand by aeration. By this means, the flow can be equalized over a period of 16 to 20 hours or more, and any ill effec-t on t.he receiving stream is greatly reduced.
Summary The trend is toward better dairy equipment with bett,er wastesaving features and better waste utilization in by-products manu-
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L i q u i d Industrial Wastes facture. Through education, the dairy plant managers and employees are becoming more and more waste conscious and, therefore, more active in waste prevention. Where treatment can be provided economically in combination with city waste, this is preferred t o separate industrial waste treatment. I n general, for separate milk waste treatment plants, the high-rate recirculating trickle filters have been found costly to install but quite satisfactory in operation when properly built and maintained. Attempts are being made to develop some type of simplified aeration plant, with or without activated sludge, t h a t will give satisfactory results a t low operating costs. The problem of economical and satisfactory disposal of sludge ‘ from trickle filters and aeration units is still t o be solved.
Literature Cited (1) Backmeyer, D., Proc. 6th 2nd. Waste Conf., Purdue Univ., 34, No. 4, 411 (1949).
(2) . , Dairv Sanitation Engineers Committee. “Dairv Waste-Saving a& Treatment Guide for Milk Plant OperrttoEs,” Harrisburg Pa., Pa. Assoo. Milk Dealers, Inc., 1950. (3) Hasfurther, W. A,, and Klassen, C. W., Proc. 6th 2nd. Waste conf., Purdue univ., 34, 424 (1949).
(4) Hoover, S. R., Jasewicz, Lenore, Pepinsky, J. B., and Porges, N., Sewage and 2nd. Wastes, 23, No. 2, 167 (February 1951). ( 5 ) Hoover, S. R., and Porges, N., Proc. 6th 2nd. Waste Conf., Purdue Univ., 34, 137 (1949). (6) Johnson, W. S., Ibid., 4th Conf., 33, No. 4, 54 (1948). (7) MoKee, F. J., Sewage and Ind. Wastes, 22, No. 8 , 1041 (August 1950). (8) Neil, D. G., Proc. 4 t h I n d . Waste Conf., Purdue Univ., 33, 45 (1948). (9) Porges, N., and Hoover, S. R., Ibid., 6th Conf., 34, 130 (1949).
(10) Porges, N., Pepinsky, J. B., Hendler, N. C., and Hoover, 8. R., Sewage and I n d . Wastes, 22, No. 3 , 318 (March 1950). (11) Ibid., 22, No. 7, 888 (July 1950). (12) Rhame, G. A., Water & Sewage Works, 94, 192 (1947). (13) Spaulding, R.A,, Proc. 4th 2nd. Waste Conf., Purdue ‘Univ., 33, No. 4,40 (1948). (14) Task Committee on Dairy Waste Disposal, Dairy Industry Committee, Milk Dealer, 39, No. 5, 88 (1950); 39, No. 6, 51 (1950); 39, No. 7, 47 (1950). (15) Trebler, H. A., Proc. I s t l n d . Waste Conf., Purdue Univ., 6 (1944). (16) Trebler, H. A., and Harding, H. G., IND. ENG.CHEM.,39, 608 (1947).
(17) Trebler, H. A., and Harding, H. G., Proc. 4th 2nd. Waste Conf., Purdue Univ., 33, 67 (1948). RECEIVED for review October 26, 1951.
AOCEPTBD January 19, 1952.
GRAIN DISTILLERIES C. S. BORUFF, HZram Walker & Sone, Inc., Peoria, Ill. Beverage distillers are recovering, drying, and marketing their destarched grain stillage as distillers dried grains and dried solubles. Some stillage is being refermented to give riboflavin and Blz feed supplements which play an important role as supplements in balancing poultry and livestock rations. Distillers dried solubles also serve commercially as a yeast growth supplement and in the production
of fungal amylase and streptomycin. Under good housekeeping practices and complete stillage recovery as feeds, the industrial waste load from a grain diaillery will possess a population equivalent of 1.0 to 3.5 per bushel of grain ground, Intraplant studies have identified the source of these wastes. High rate trickling filters or anaerobicdigestion may be used to stabilize the waste where necessary.
ASTES from U. S.graindistillerieshave been progressively and materially reduced since the repeal of prohibition in 1933. Team research and development in the fields of chemistry, chemical engineering, biochemistry, nutrition, and marketing, along with capital investments, have taken grain distillers “slop” out of the category of a waste and converted it t o important byproducts, Even its name has been changed-namely, from slop t o stillage. Products now recovered or produced from stillage have become profitable items of commerce for t h e distillers. A 1949 survey by the Distillers Feed Research Council, Inc., shows t h a t 85% of all grain beverage distillers’ stillage is now being dried and sold as feeds, 14% is fed wet, and only 1% is wasted.
only few evaporators were used in preprohibition days t o concentrate the thin stillage-liquid that passes through the screenstoday most beverage distillers evaporate these solubles t o a 25 t o 40% solids sirup and dry them with their screened grains t o produce distillers dried grains containing solubles (dark grains). A number of distillers drum-dry part of their evaporated solubles t o produce distillers dried solubles. This latter product was the result of post-repeal research and was first placed on the market in 1939. A large number of distillers now produce both dried grains containing solubles and dried solubles (see Figure 1). The history and more complete descriptions of the various processes employed in processing grain t o whisky and alcohol and the recovery of the above three distillers feeds have been published elsewhere (1, 4, 7, 9-11, $2, 93). The effect of using various grains and manufacturing processes on the chemical and vitamin content of distillers feeds has also been reported (1-4, 19,dO, 99,$3). T h e role of these products in producing balanced poultry and livestock rations has been covered in a number of publications of the Distillers Feed Research Council, Inc., Cincinnati, Ohio, and elsewhere (1, 19, 20, $9,$3).
Recovery of Stillage I n brief, the processing of grain to alcohol, carbon dioxide, and distillers feeds involves the milling and cooking of the grain, converting t h e solubilized starch to grain sugars by adding malt, fermenting with yeast, and then distilling off the alcohol or whisky (see Figure 1). T h e carbon dioxide developed during t h e fermentation is recovered in some of the larger plants and converted to dry ice. T h e de-alcoholized fermented mash from t h e stills (called stillage) contains from 5 t o 7% solids, possesses a biochemical oxygen demand of around 25,000 p.p.m., a p H of 3.6 t o 4.0, and amounts t o about 40 gallons per bushel of grain mashed. The 17 t o 19 pounds of solids contained in the stillage produced from one bushel of grain are about half suspended and half dissolved. Commercial screens of various designs will separate 8 t o 9 pounds of these solids. When dried in rotary steam dryers these screenable solids become distillers dried grains, a product known in the trade as light distillers grains. Although
March 1952
Special Uses for Distillers Solables Grain distillers screened stillage (2.5 t o 3% solids) and distillers dried solubles have, within the past few years, been found t o be excellent media for a number of biological processes. I t s high soluble protein and vitamin content was first utilized as a yeast supplement by various distillers. The production of a malt replacement enzyme concentrate, fungal amylase, has been reported and used t o a limited extent commercially ($6). Dried distillers solubles are also being used in the media for commercial antibiotic production, mainly streptomycin (16, 1 7 ) . The pres-
INDUSTRIAL AND ENGINEERING CHEMISTRY
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