September IBSO
Industrial Ulustes Kentucky distilleries convert spent mash to a profitable animal food and treat remaining wastes so that plant effluent is not damaging to receiving streams
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blue ribbon winner in the Blue Grass country of Kentucky is not always the comely thoroughbred race horse who receives world-wide adclaim. This columnist prefers to select the aggressive Bourbon whisky plants which dot this famous countryside. Our applause is not directed to the admittedly fine quality of the whisky produced in these distilleries, but is directed to those Kentucky distilleries which have pursued their stream pollution problem persistently over the years and can today report completed action in solving this troublesome condition. Kentucky produces the major portion of our country’s Bourbon whisky in over 60 distilleries located essentially in the Blue Grass area. If the spenbmash wastes from these distilleries were not processed, this industry would pollute receiving streams with raw sewage equivalent to three times that from the 2,800,000residents of Kentucky. Today, the distillery waste to streams is practically insignificant as a 99.9% reduction in the potential biochemical oxygen demand (B.O.D.) of the spent mash has become reality in the larger distilleries. Thirty years ago, Kentucky distilleries were much smaller than today, so the amount of spent mash in each locality was relatively small. Then, this waste was disposed of by maintaining large cattle pens as part of the distillery operations. A distillery using 100 bushels of corn per day required 100 head of cattle to consume their waste. As the distillery grew in capacity it faced a difficult disposal problem since the odors, flies, and other objections involved in raising cattle on a small plot of ground were serious nuisances which restricted possibilities for expanding whisky production. The industry was forced to find more sanitary methods for disposal. The problem was complicated so the corrective method had to be developed stepwise. Proof that the spent mash made a good food for raising cattle had been proved. It was therefore apparent that if the suspended solids could be separated from the solution and then dried so that the nutritional factors in the spent mash were preserved, then this dried product could be sold commercially provided the process was an economical method. This engineering and animal husbandry study involved research on methods for dewatering and drying the insoluble product. Years of study in this development were necessary before a satisfactory inexpensive operation was found. The next inroad on pollution was evaporation of the residual solution and drying of the concentrate to a solid soluble food product in which were preserved the original vitamin, enzyme, and other food values. With this step accomplished the third and final problem was to treat all other residual plant wastes from the distillery and dryhouse operations BO that the B.O.D. and other undesirable aspects of these waste waters were corrected sufficiently to permit disposal of the treated waters to the stream. This author is pleased to read the completed answer to the problem (I), particularly because in addition to disposal correction the process haa created an economical utilization of a troublesome waste. HE
Corn is the essential ingredient for producing Bourbon whisky. It is ground to a meal and then made into a mash by adding 20 gallons of water for every bushel of corn used. This mash is added to a cooker and heated with steam for about an hour in order to soften the meal constituents. The product is then cooled rapidly by vacuum to a determined temperature, and some rye mash is added in aniounts determined by the particular qualities desired in the whisky. Barley malt is then added promptly to the mash. The enzymes convert the starches in the mash to sugars. The next step is to convert these sugars to alcohol, so after further cooling by vacuum, a prepared yeast and a definite amount of “back slop” (spent mash filtrate) is added. The mash is allowed to ferment in large cylindrical tanks for 3 to 4 days until all sugars are converted to alcohol. The fermented mash is then discharged to a large storage tank where under the name of “beer” it is ready for distillation. The still is equipped with numerous perforated plates, down through which flows the beer against a rising steam vapor introduced at the bottom. The alcohol distills upward and out the. top to the condenser. This raw first run of whisky is redistilled and refined to produce Bourbon whisky. The dealcoholized beer which discharges from the bottom of the still constitutes the disposal problem. It is usually called “spent mash,” “still slop,” or “whole stillage.” The solid content of s nt mash varies considerablydepending on the particular crmula used in the whisky proceas. On the avera e the beer fed into the still amounts to between 33 and 45 atons per bushel of grain used. The spent mash has a B.O.%. between 20,000 and 50,000 p.p.m. and a total solids of 5.5 to 11.5%. A pH between 3.6 and 4.6 indicates why the mash carries disturbing quantities of copper originating from acid corrosion of the rocessing equi ment. The copper interferes somewhat wit! bacterial metEods for disposal of the spent solutions. Extensive studies, however, have shown that by anaerobic digestion followed by a final trickling-filter treatment a practical means for disposal exists. However, the recovery of the solids and the valuable vitamins, protein, and yeasts in the spent mash is more practical for it provides utilization of the waste and an economic recovery profit. This utilization method is now standard with the industry. The spent mash leaving the still is pumped to the dryhouse ?here it passes over a series of gravity, vibrating, and gyrating screens. The fluid s nt mash which passes the first gravity screen is called bacglop; a portion of this is used back in the fermentation step to serve as a nutrient for the yeast. The thin water material which passes through the other screens is called thin slop and is collected in a tank for feed to evaporators. It contains 2.5 to 5.5% soluble solids. Multiple effect evaporators of s cia1 design reduce the water content to a sirup of about solids. This sirup is usually fed between two steam-jacketed drums with faces revolving in close contact with each other. The film of sirup dries on the hot drums as the rotate. The dried product which is scra continuously &om the drum contains 8% water and is pac ed for sale as cattle food. (Continued on paga 180 A )
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Industrial Wastes The material which does not pass through the screens averages about 83% water content and is called "screenables." The water content is reduced further by mechanical squeezing methods. This step has required a long series of developments to attain masinium reduction in water content. Earlier methods were to feed the screenables ontoaperforated belt which passes between two pressure rolls. Today the more modern practice is to feed the screenables between two perforated steel disks which are set at a wide angle to form a V. Each disk is rotated slowly and as the waste moves down into the slot in the V-disks, a substantial portion of water is pressed out, leaving the pressed cake with 65 to 70% moisture. This pressed cake is then fed to inclined rotary steam-tube dryers, so that the wet cake as it enters the upper end tumbles in and around the hot steam tubes. As it leaves the lower end of the rotating dryer it is cooled and packed at about 8% moisture content for shipment as stock feed. If drum dryers for processing the evaporator sirup are not available, this sirup is added to the dried screenables (light grains) to produce a concentrated cattle food sold as dark grains after subsequent drying in a separate rotary dryer. l b s i d u a l plunt maastea
It is evident that the above treatment and utilization method includes only the spent mash by-product froiii the still. Besides this waste there are about 100,000 gallons per day of contaminated waters on the basis of a 3000-bushel distilling plant. The solids and B.O.D. values are shown in the following table : Gal./Day Evaporator condenPete Plant and equipment wash-ups Coolinq tower overflow Beer still residues Domestic sewage Total
46,000 21.000 24,000 3,000
7,000
Total Solids, B.0.D
P.P.M. P.P.M:' 130 1050 1100 240
830 e 10
___.
100,000
600 1000 550 1000 200
670
B.O.D., Lb.
226
176 110 26
14 55 1
I _
Attempts to treat this combined waste by the activatedsludge process have not been practical because the copper in the evaporator condensate contains 6 to 25 p.p.m. copper which concentrates in the sludge and reaches a toxic level. In the trickling-filter method copper appears to have no effect on the operation and an average reduction of 93% B.O.D. is experienced. In one installation a trickling filter is operated with a primary and secondary clarifier with a high circulation rate of 4 to 1 because of high B.O.D. of the raw waste. One half the filter effluent goes to the secondary clarifier and the other half is returned to the primary for clarification. Sludge from the clarifiers is either stored or digested in the loirer compartment of the primary clarifier which is actually a conibination clarifier and digester. The trickling filter is designed for a low water loading of 8,000,000gallons per day with a B.O.D. loading of 0.75 pound per cubic yard at a filter depth of 6 feet. To overcome ponding of the filter 3- to 4-inch media are used. The effluent is chlorinated before disposal to the stream. The material balance of the wastes from a typical 3000bushel distillery is about as follows: B.O.D. Iloduotion, % Lb.7 OvarAmount P.p.rn. day U n i t all 780,000Ib./day" 40.000 30,000 , 56,000 lb./day 100,000 wal./day 670 ' 5bO 9k'. i '48.2 100,00OgaI./day 4.5 3 8 . 5 !U.0 9 0 . 9
Effluent
Source Tyue Distillery Still ~ O I J Dryhouse Dried feeds Dryhouse Waste wat.rrsb Disposal Final plant At 31 gallons per liualial. b Including distillery wash
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Literature cited (1) Davidson, A. B.,.S'eawgp u w i I d . Wastes, 22, No. 5 (1,950).
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