Treatment
of Vegetable nnery Wastes (Above) TYPICAL FILL-AND-DRAW CHEMICALTREATMENT PLANT
The location of vegetable canneries close to sources of raw produce, the seasonal nature of their operation, and the large volumes of waste combine to produce a waste disposal problem peculiar to the canning industry. Wastes produced incidental to the canning of vegetables are classified into four groups : cooling tank water, silage juice from pea and corn canneries, gross solids, and processing water. The characteristics and methods for disposal of each of these types of waste are discussed. The processing waste water of the principal vegetable packs-peas, corn, and tomatoes-has a B. 0.D. usually between 1000 and 4000 p. p. m. Five methods of treatment are described: screening, chemical precipitation, biological filtration, and discharge to.an impounding lagoon or to a municipal disposal plant. Frequently two or more of these treatments are required. The use of sodium nitrate to control odors in lagooned wastes and soda ash in a highrate trickling filter are discussed.
FOR
VEGETABLE WASTES
(Right) D R Y I N G BEDS FOR SLUDGE PEODUCEDBY CHEMICAL TREATMENT
N. H. SANBORN National Canners Association, Washington, D. C.
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HE treatment and disposal of waste from the food processing industry is a subject which yearly increases in importance. The rapid growth of the canning industry, the variety of products packed, and the seasonal nature of its operations, which for most canning plants means an operating period of one to three months, has made difficult any investigation and experimentation on cannery wastes. The canning of fresh vegetables constitutes an important portion of the canning industry’s output. I n 1940, a fairly representative year, 174 million cases of vegetables were canned out of a total pack of approximately 399 million cases. Canning procedures necessitate the use of large volumes of water, utilized principally in washing raw produce, blanching, cooling processed cans, and maintaining sanitary conditions within the factory. As a general figure it may be stated that 25 gallons of waste water contaminated with organic material are produced per case of twenty-four No. 2 cans. A notable exception occurs in the canning of tomatoes and tomato products where the waste produced may vary anywhere from 3 to 100 gallons per bushel of tomatoes (8). The total waste discharged from the canning of vegetables during 1940 was approximately 4 billion gallons, exclusive of cooling tank water. Vegetable canners are generally located in small communities in the agricultural areas where, during summer months,
streams are small and sluggish and poorly adapted to receiving substantial organic loads. Likewise local disposal plants seldom have the required capacity to treat raw cannery waste. A careful consideration of the volume and characteristics of the cannery waste and degree of treatment required, as determined by a preliminary survey is of fundamental importance whether the cannery waste is to be discharged to a receiving stream or to a municipal plant. Obviously, and due consideration has not always been given to this point, the survey should be conducted a t times of maximum production and suitable allowance made for possible expansion in cannery operations. 911
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Usually some form of treatment is necessary, and a preliminary survey of the situation should include the following data: volume and characteristics of the waste, degree of treatment required, area and topography of land available for treatment plant, possibilities of utilizing local municipal treatment works if any exist, and financial considerations. K i t h respect to the latter, consideration must be given to the fact that the canning industry is essentially a seasonal one of short duration. After obtaining the above information, it is possible to adapt one of the following methods of treatment: screening, chemical precipitation, biological filtration, discharge to an impounding lagoon, or discharge to a municipal treatment plant. SELECTRO VIBRATISG SCREEN FOR SCREENISG CANKERY WASTE,i~IUPORTANT STEP IN
ITSTRE.4TMEST
Types of Waste Wastes produced by a vegetable canner fall into four groups, each of which requires separate consideration: COOLINGTANKWATER. There is little or no organic content. This clean water should be discharged directly to a receiving stream or storm sewer. Its value as a diluent of strong liquid wastes does not justify the cost of a larger treatment plant. PEAOR CORNSILAGEJUICE.This juice is derived from the practice of stacking pea vines or cornhusks, corncobs, and immature ears in open stacks or silos. Ensilage is sold as cattle feed. The exuding silage juice contains a high concentration of soluble organic solids. The 5-day B. 0. D. of pea silage juice from an open stack was found to be 61,000 and 78,000 p. p. m. from a covered silo. Corn silage juice has a B. 0. D. of approximately 30,000 p. p. m. Silage juice has a strong disagreeable odor and a pH of about 4. To facilitate collection of silage juice, silage stacks should be provided with a concrete base and drainage discharged to an underground collecting tank. Seepage of silage juice has been the cause of numerous complaints. The most satisfactory method of final disposal is by hauling the juice to an isolated place where dumping will not create odor nuisance or the juice may be discharged a t a very slow rate into a stream during the following spring a t times of high stream flow. GROSSSOLIDS. Solid material, other than that utilized as silage, is obtained from discarded raw material, trimmings, cleanup operations, and screenings. This waste, in so far as vegetable canners are concerned, offers little opportunity for by-product utilization. It is generally returned to fields for its organic matter, dumped in isolated spots, or given to farmers for hog or cattle feed. With tomato waste a few canneries recover the seeds or dry the solids for sale as feed. PROCESSING WATER WITH ORGANIC CONTENT.Waste water from washing operations, blanching, spillage around fillers, and cleanup operations contains organic matter in solution and suspension, together with more or less large pieces of vegetable material. The successful disposal of this type of cannery waste frequently presents difficulty. The characteristics of cannery waste vary considerably even for the same raw product, according to the canning procedure employed. I n general, the 5-day B. 0. D. of waste (after screening) produced in the canning of peas, corn, or tomatoes lies between 1000 and 4000 p. p. m.
Screening -
Efficient screening of cannery waste is essential, regardless of further treatment that may be necessary. Rotating screen units equipped with strong water sprays to prevent screen clogging are in general use. The New York State Board of Health (6) suggests screening a t the rate of 3.5 gallons per square foot per minute; a 40-mesh wire screen is recommended for wastes other than tomato, and a 20-mesh screen for tomato waste. During the past two or three years the use of vibrating screens has gained considerable favor. With this type of unit equipped with a 40-mesh wire screen, pea,
ONE OF SEVERAL TYPESOF ROTATIKG SCREEXS USED FOR CANNERY KASTE
corn, tomato, and lima bean wastes have been successfully handled a t rates varying from 32 to 70 gallons per square foot per minute. The solids removed by vibrating screens are more compact and drier, and hence more easily handled. Mechanical screening as the sole method of treatment will be suitable only when sufficient stream dilution is available.
Chemical Precipitation Chemical treatment of screened cannery waste may be used to reduce pollutional strength further. This method has received considerable attention ( 2 , 6, 0, 10). Discussion will be confined to studies conducted in Wisconsin ( 9 ) where many such installations are in operation. Two types of chemical treatment plants are in use, the continuous-flow and the fill-and-draw or batch treatment. With either type the same coagulants are used-namely, high-calcium hydrated lime followed by either ferrous sulfate
INDUSTRIAL AND ENGINEERING CHEMISTRY
August, 1942
or alum. Chemical coagulation of cannery waste is always conducted a t a high pH, 10 to 11, and requires a chemical dosage much greater than that used for domestic sewage or combined domestic sewage and cannery waste. Typical chemical dosages per thousand gallons of screened waste are as follows: Waste Pea Beet Corn Carrot Tomato
Lime, Lb. 7 10 9 5 4
Other Chemical, Lb. 3 ferrous sulfate 4 ferrous sulfate S ferrous sulfate 1 ferrous sulfate 1 alum
If properly conducted, chemical treatment will effectively remove suspended and colloidal solids but not such materials as sugars which are in true solution. The degree of treatment will therefore depend upon the relative proportion of suspended and colloidal solids to soluble organic solids. An analytical determination of the soluble organic and suspended organic solids of a cannery waste cannot be used to determine the effectiveness of chemical precipitation because certain colloidal solids which are more or less completely removed by chemical precipitation are reported as soluble organic material. That such actually is the case is shown by considering the data obtained in a series of eleven treatments of corn waste by the fill-and-draw method, using lime and ferrous sulfate as coagulants. The volume of corn waste in each treatment was 11,350 gallons. By analysis, the raw screened corn waste contained an average of 1750 p. p. m. soluble solids and 800 p. p. m. suspended solids, a total of 2550 p. p. m. organic solids. If the chemical treatment had removed only the suspended solids, the efficiency would have been 31 per cent. Analysis, however, showed that the chemically treated waste had an average of 844 p. p. m. of total organic solids, a removal of 67 per cent. The average reduction expressed in terms of 5-day B. 0. D. was 78 per cent. This B. 0. D. reduction may be somewhat high since standard bicarbonate water was used in these determinations. More reliable B. 0. D. determinations have been obtained on cannery wastes, particularly chemically treated wastes, by the use of supplemental dilution water as recommended by Lee and Nichols (4).
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Lack of flexibility in maintaining optimum chemical dosage rates and inability to remove completely the large volumes of sludge produced are the chief objections to the use of the continuous-flow type of treatment. These difficulties have been eliminated by the fill-and-draw treatment. Briefly, this method involves pumping screened waste in one of two or three treatment tanks. When this is full, the flow of waste is diverted into the second tank. The agitator in the first tank is started, the required amount of lime is added, and then half the calculated amount of the second chemical is added. Agitation is continued for several minutes, and the remainder of the second chemical is added slowly until the %flocis curdy in appearance, and shows a tendency to settle rapidly and leave a clear supernatant liquid. Somewhat more or less than the calculated amount may be required according to the nature of the particular batch under treatment. The floc is allowed to settle and the clear supernatant liquid is discharged through ti floating discharge pipe. Sludge is discharged to sludge beds. Chemical treatment has proved satisfactory a t a number of canneries, where stream dilution had been insufficient, and also as a means of pretreatment prior to discharge to a municipal treatment plant. The cost of a fill-and-draw treatment plant for a two-line cannery is approximately $3000. Operating costs, including all fixed charges, amount to approximately $0.01 per case of twenty-four No. 2 cans of pea waste. For larger canneries construction and operating costs are proportionately somewhat less.
Biological Filtration
Relatively few biological filters are operated by canners. The large initial investment, necessity for conditioning filters prior to the canning season, and lack of outstanding performance of existing filters due to overloading have discouraged this type of treatment. Experimentaliv it has been shown that high-rate biological filters with recirculation to secure six passes of the waste through the filter reduce the oxygen demand by approximately 70 per cent (9). A further reduction of 10 to 15 per cent may be obtained through a settling tank providing - a detention of one hour. Because of this overloading, canneryoperated high-rate filters discharge an acid effluent. The same situation obtained a t a municipal high-rate filter whose load consisted of approximately 99 per cent cannery waste. With overloaded filters of this type satisfactory pH control by means of lime has not been attained. The alkalinity produced by lime is effective in only part of the treatment plant because the large amount of carbon dioxide produced in the filter effectively precipitates the lime as insoluble calcium carbonate. Soda ash, which is not affected by carbon dioxide, remains in solution and is effective in correcting acidity until completely neutralized by organic acids. Its effect extends, therefore, from the point of application through the primary tank, filter, and secondary clarifier. During the past summer, tests were made a t the above-mentioned municipal treatment plant using soda ash to control pH (6). A marked improvement in filter efficiency was obtained. For example, when pea waste was applied without the addition of soda ash t o t h e high-rate filter a t t h e high loading rate of 2.7 cubic feet of rock per pound of B. 0. D., the average p H LINK-BELTVIBRATING SCREEN,YIELDINGSCREENINGS THATARE COMPACT AND FREEFROM ADHERING LIQUID of the secondary clarifier was 6.1. The
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combined filter and Shallow lagoons are secondary clarifier necessary to permit efficiency was 30.0 maximum distribution of absorbed p e r c e n t . On oxygen. This another run soda ash was added. The method of odor control was successfully filter loading was e m p l o y e d for a slightly greater, 2.5 cubic feet, final pH strong waste from a large corn can6.9, and filter and nery. Studies on secondary clarifier this lagoon were efficiency 49.3 per conducted by the cent, an increase of Illinois State Board 64 per cent in effiof H e a l t h ( 1 ) . ciency. I n another Sodium nitrate was series of tests with supplied to satisfy corn waste, part of 20 per cent of the the cannery waste initial5-dayB.0.D. was by-passed to a t a cost of $0.0035 secure data a t lower per case of twentyfilter l o a d i n g s . four No. 2 cans. With the filter loadWhile the lagoon ing at 6.4 cubic feet itself was not enand no addition of tirely free from obsoda ash, the final pH and efficiency jectionable odors, the odors did not were 7.6 and 78.4 extend beyond 200 per cent, respecfeet from the lagoon tively. Anincrease even under optiin filter loading to mum odor-produc4.6 cubic feet and ing conditions. No addition of soda ash complaints either t o t o secure a final pH t h e c a n n e r or of 7 . 7 g a v e a n to the State efficiency of 79.0 (Above) HIGH-RATEBIOLOGICAL FILTER FOR TREATMENT O F CORN WASTE, Board of Health p e r c e n t . ConIN PROCESS OF CONSTRUCTION; (below) DISTRIBUTING SYSTEM ON A HIGH-RATE were made, in t r o l of p H b y BIOLOQICAL FILTER contrast to numers o d a ash acous complaints recomplished t h e ceived in previous years. Halvorson (3)treated corn waste samedegree of efficiency as increasing the filter capocity by 40 by a combined lagoon and trickling filter. Lagooned wastes per cent. Filter odors and thick scum accumulation on the are applied to the filter a t a rate of 20 million gallons final clarifier, which accompany low pH flter effluents, were per acre per day and returned to the lagoon. The filter eliminated by the use of soda ash. was designed to treat approximately 10 per cent per day of the maximum volume expected in the lagoon. The cost Discharge to an Impounding Lagoon of treatment including fixed charges amounted to $0.0087 per case. Probably the earliest device used by the canning industry t o eliminate stream pollution consisted in discharging waste to an impounding lagoon. Increased production of canned Discharge to a Municipal Treatment Plant foods and more stringent stream pollution regulations are The treatment of cannery waste a t municipal disposal factors making this method more important. Assuming plants presents many problems. The volume and strength of that cheap land is available and that the lagoon is properly most vegetable canning wastes exceed the domestic sewage constructed to prevent seepage into a near-by water course, in nearly all communities where canneries are logated. Studthe most important consideration is that of odor control. ies conducted in Wisconsin indicate that a minimum of 80 Odor emanating from an untreated lagoon of cannery waste cubic feet of filter media per pound of 5-day B. 0. D. per day is unpleasant. The use of activated carbon, lime, or chloriis required on standard filters to secure satisfactory treatnated lime is not satisfactory. Laboratory and small-scale ment ( 6 ) . The cannery wastes in these studies had been field studies have demonstrated that odor control is possible pretreated by chemical precipitation a t the canneries and by the use of sodium nitrate (7). Cannery wastes undergo arrived at the municipal treatment plants in an alkaline two-stage decomposition. The first period of greater decondition. With untreated cannery waste, pH adjustment composition occurs during a relatively short time. Normally is necessary; otherwise the filter efficiency is lowered and this would proceed as anaerobic decomposition with the poor clarification obtained in the final settling tank. Raw production of offensive odor. If, however, sodium nitrate screened vegetable wastes can be successfully treated as shown is added to the waste, nitrate oxygen is available for aerobic by the operation of the trickling filter plant a t Bowling Green, decomposition and no offensive odors are produced. The Ohio, the activated sludge plant a t Celina, Ohio, and several second period of decomposition occurs slowly over a long others. The treatment of all cannery waste at municipal period of time. Absorption of atmospheric oxygen, and disposal plants would be most desirable, but much technogrowth of green algae and higher forms of aquatic life permit logical information remains to be obtained before this goal odorless decomposition of the remaining organic material.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
can be reached. The financial arrangement between the canner and municipality is, in the last analysis, the determining factor.
Literature Cited (1) Black, H. H., Canning Age, 23, 325 (May,-1942). (2) Eldridge, E. F., Mich. State Coll. Eng. Expt. Sta. BUZZ.78 and 83 (1938). (3) Halvorson, H. O., “Rept. on Studies of Cannery Wastes”, Minnesota Canners Assoc., 1940. (4) Lee, W. L., and Nichols, M. S., Sewage Works J., 9, 34 (1937).
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(5) Natl. Canners Assoc. in cooperation with Wis. State Board of
Health, unpublished data. (0) New York State Dept. of Health, “Treatment of Canning .. , (7) Sanborn, N. H., Canner, 92, No. 16, 12 (1941). (8) U. S. Public Health Service, “Ohio River Pollution Survey, Industrial Waste Guide, Tomato”, 1939. (9) Warrick, L. F., McKee, F. J., Wirth, H. E., and Sanborn, N. H., Natl. Canners Assoo. Bull. 28-L (1939). (10) Wisconsin Stata Board of Health, “Treatment of Pea Cannery Wastes”, 1926.
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PRESENTED before the Division of Water, Sewage, and Sanitation Chemistry at the 103rd Meeting of the AMERICAN CHEMICAL SOCIETY, Memphis, Tenn.
Solubilization of Water-Insoluble Dye in Aqueous Solutions of Commercial Detergents J.
w.
MCBAIN AND R. C. MERRILL, JR. Stanford University, Calif.
HE multiplicity of detergents and wetting agents
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recently made available has been accompanied by an equally great variety of applications in practically every industry. Comparative measurements on any one of the properties are therefore of great interest. Most of them belong to the class of solutions known as colloidal electrolytes, first defined by McBain in 1918 as electrolytes in which at least one of the ions is replaced by a micelle or colloidal aggregate. Probably all soluble ionizing organic compounds containing more than nine or ten carbon atoms belong to this class.
Solubilization One of the most unusual properties of a detergent solution is its ability to dissolve otherwise insoluble materials. This phenomenon has been known and used commercially since 1874 @),Lysol being the most familiar example; but only recently has much attention been paid to the mechanism involved. In 1908 Nottbrack (1.4)used the solvent power of 20 per cent aqueous Turkey-Red oil to obtain solutions of dyestuffs not soluble in water, and found that the amount of sulfonated oil necessary depended on the dyestuff and the concentration desired. Engler and Dieckhoff (3) in 1892 solubilized benzene, toluene, xylene, and turpentine in various soap solutions. Witt (20) in 1915 stated that the alkyl naphthalene sulfonic acids possessed an “astounding capacity for dissolving all manner of substances which are quite insoluble in water-including resinous by-products of sulfonation and the CaSOl formed by neutralizing the reaction mixture”. Since then many other examples have appeared in the literature (2, 6, 6, 7, 16, I?’), notably the work of Smith (18) who showed that 10 per cent sodium
Soaps, soaplike substances, and many others, such as bile salts and the inn umerable detergents now commercially available, have the property of solubilizing waterinsoluble materials, such as an oil-soluble dye, by incorporating the latter in or upon the colloidal micelles that are the distinctive feature of all these colloidal electrolytes. Measurements are given which compare examples of a large variety of such detergents, including some that are nonelectrolytes. Similar observationsare noted for nonaqueous solvents. There is no connection between wetting power and solubilization. Heat increases the amount solubilized, as does the addition of salts in concentrations where the detergent is not yet fully colloidal. In concentrated solutions, added salt decreases solubilization. oleate solutions were able to dissolve all common insoluble organic liquids. McBain and McBain (9) were the first to realize the theoretical importance of this phenomenon for colloid chemistry and critically to establish its actual occurrence. Solubilizing consists of the incorporation of a material in the colloidal micelles of the detergent. These micelles are thermodynamically stable, both before and after solubilization. Incorporation of the insoluble material usually decreases further solubilizing power. Thus, a stable emulsion of benzene may be formed in one per cent sodium lignin sulfonate, but if a dye is already present, the emulsion breaks readily.
