Liquid Industrial W u s t e s Conelasions
Literature Cited
1. I n the high level, liquid radioactive wastes resulting from operations in the atomic energy programs, a very small concentration of the radioisotopes (fission products) are required to produce tolerance dosages and thereby render and create a hazard in discharge of such wastes to nature. 2. Tolerance concentrations and operations practices must be reconciled with environmental and economic considerations. 3. The principle of concentrat'ion and confinement is the most likely approach t o resolution of t,hese operating problems. 4. A comprehensive research and development prograin has been under Ray in this field with proved processes now in use. 5 , The continued expansion of the atomic energy industry into new projects involving still higher levels of radioactivity presents a definite challenge t'o chemists and chemical engineers. 6. The future gron-th of this industry from the experiment'al phase through the applied use of the products may well depend on its ability to find increasingly effective and economical methods of processing and disposing of its hazardous waste product's.
(1) &lyres,J. A . , IND. ENG.CHEM., 43, 1526 (1951). (2) McCullough, G. E., Zbid., 43, 1505 (1951). (3) Manowits, B., and Bretton, R . H., Upton, S . Y . , Brookhaven National Laboratory, BKL-90 (Oct. 1, 1950). (4) Plutonium Project, J . Am. Chem. Soc., 68, 2411 (1946). (5) &anford Research Institute, "The lndustrial Utilization of Fission Products; a Prospectus for Management" (March 1951) (also AECU-1269, C . S. Atomic Energy Commission, Tech. Inform. Ser., Oak Ridge, .Term.). 16) , , Tomakins. . E. R.. Khsm. J. X., and Cohn, W.E., J . Am. Chem. Soc., 69,2769 (1947). (7) U. S.Atomic Energy Commission, Isotopes Division, Oak Ridge, Tenn., "Interim Recommendations for Disposal of Radioactive Wastes by Off-Commission Users," Ci.rc. B-6. RBCEIVED f o r review September G , 1951.
ACCEPTEDJanuary 24, l Q j 2
ITS INDU HARRY 11-.VON ILOESECKE, Bicreau of Agricultural arad Industrial Clremistru, Agricultural Research Administration, Washington 25, D. C. been made in profitable utilization of the solid wastes and the more concentrated liquid effluents, but the more dilute effluents still offer pollution problems. Private industry, state, and federal agencies are engaged in attempting to find practical and economic disposal methods.
Increased processing of citrus fruits has created huge amounts of both solid and liquid wastes, the former estimated to be about 3,500,000 tons annually and the latter 4 billion gallons, varying in B.O.D. from approximately 100 to 100,000 p.p.m. Considerable progress has
ucts, for about 6OY0 of the fruit remains as peel, rag, and seeds. Liquid effluents are produced in canning the juice and sections and in preparing feed, citric acid, and pectins. It is estimated that in 1949 solid citrus wastes amounted to about 3,500,000 tons, \Thereas liquid effluent,s xere in the neighborhood of some 4 billion gallons, varying in B.O.D. from approximately 100 t o 100,000 p.p.m. I n Orange County, Calif., a survey (13) showed that waste from processing oranges, lemons, and grapefruit amounted in 1947 t o from 41 t o 845 tons of B.O.D. per month. That there is pollution of &earns by citrus cannery effluents has been recognized b y t h e President's Water Resources Policy Commission. The commission states (32) that in Florida, one of the vacation
:e: better understood.
-
200,000
Types of Waste
,80,000
Different types of waste encountered in citrus processing may be classified as:
TOTAL PRYDUCTION
160,000 ,40,000
,20,000
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20,000
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80,000
Solid
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-20
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-I0
Cannery- waste consisting of peel, rag, and seed Screenings from citrus pulp drying effluents Sludge from peel oil preparation Residues from plants producing citric acid and pectins Still s16psa
USED FOR P6OZ€S5/NG
*
Liquid
PROOUCT/ON O f fR0ZEN CONCEMRA7€5 S7HRl€D
YEAR 1
1
1
1
1
1
I
I
~
Cannery effluents Pulp drying plant effluents Distillery effluents" Effluents from citric acid and pectin plants
Liqutd Idustrial WasteEffluents from citrus molasses plants . Effluents from peel oil plants Effluents from fresh fruit packing houses At present probably about 90% of the solid waste is dried for feed purposes in Florida, and considerable quantities of the liquid effluents have been concentrated and sold as citrus molasses t o the economic advantage of not only the citrus grower but also the processor. The amounts thus utilized vary according to the molasses and feed markets. McNary ( I O ) estimates that during the 1945-46 season in Florida 60% of the solid waste was dried for feed.
Solid Wastes A great deal of this material is now used for the production of peel oils, seed oil, pectins, cattle feed, and brined and candied peel. The approximate composition of the solid residue is given in Table I.
Table I.
Analyses of Citrus Cannery Waste
California Florida Grapefruit (161, % . Rag (15), Peel Rag % 16.71 15.60 Total solids Aeh n 74 n 7.5 Volatile oil 0.43 ... Acid, as citric 0.74 0.63 Crude fiber 1.71 1.44 Crude protein ( N X 6.25) 1.13 1.06 Crude fat (ether extract) 0.28 0.16 Total s u m r (as invert) 6.35 6.30 Pentosans ' 0.83 0.44 Pect,in (calcium pectate) 3.10 3.56 0.40 0.10 Nrtringin
T:$?izt &zn\d;:
the waste at the rate of 200 t o 400 pounds per ton, an exothermic reaction took place and eventually the material became dry and crumbly. The dried mixture was unstable in that there was a gradual loss of ammonia and no guaranteed analysis could be given. Sometimes nitrates, ammonium sulfate, and superphosphate were added along with the calcium cyanamide (9, 25). Earlier, fresh lemon waste was returned t o groves in California (14). This technique has the disadvantages of the danger of spreading certain citrus diseases and the breeding of flies. Attempts have also been made to utilize the solid waste in the preparation of plastics (37), but this has not been realized commercially. About 30 years ago, lemon residue, estimated t o be between 25,000 and 35,000 tons annually in California, was subject to destructive distillation on a laboratory scale (1.4). On the basis of this work, 1 ton of the wet residue would yield about 6 pounds of acetic acid, 4 pounds of methanol, and pound of acetone, besides an undetermined quantity of gas; charcoal was left as a residue. The scheme apparently did not promise economic application and the idea never went further than the laboratory, but it was an attempt t o dispose of lemon residue which was starting t o be a problem.
Rag (14), %
200
__"I
Preparation of peel oils and pectins results in a solid residue, which may subsequently be dried for feed, and of effluents which must be disposed of so that they will not result in a public health nuisance. Preparation of feed in most cases also results in a liquid effluent of high B.O.D., as described later. Solid wastes may also be allowed t o decompose on wastelands, through enzymatic and bacterial action. A method in use about 7 years ago in a California plant handling approximately 750 tons of fruit a day has been described by Hall (6). Waste products, including peel, were flushed with water t o a central sump in the plant. From the sump the entire mass was pumped through rotating screens t o separate solids from liquids. These solids were put in large silos or storage banks and allowed t o disintegrate. As rotting progressed, trenches were cut through the mass of pulp, and the liquid which collected was pumped to settling beds together with the liquid effluent from the screens. These settling beds consisted of sand and gravel filters. The flooded beds were allowed to stand until the liquid had seeped away or evaporated. Sludge left in the beds was raked off, when dry, and burned. This is essentially the method used today for two large processing plants in California. I n one instance, part of the settled liquid in the settling beds is used for irrigation of crops grown nearby (18). The greater part of the liquid effluents from citrus processing plants in California is screened, and sometimes permitted to settle, and then discharged into municipal sewage systems (18). It has been suggested (19)that the waste be made into a slurry and fermented with Clostridium acetobutylicum t o yield alcohols, ketones, aliphatic acids, and partially demethylated pectins. As far as is known, this has never been attempted in the United States. It would probably contribute little t o solving the waste disposal problem because there would be the still slops t o dispose of. About 20 years ago in some citrus producing areas of the United States, cyanamide was added to the ground waste, the product to be used as a fertilizer. When calcium cyanamide was mixed with
March 1952
1
IO0
Figure 2.
J
Production of Citrus Pulp and Citrus Molasses
By far the most successful means of disposition has been t h e drying of the waste for cattle and dairy feed. This industry has grown considerably, and during the 1949-50 season in Texas and Florida alone, over 170,000 tons of dry citrus pulp were produced, with a value of about $5,000,000 (Figure 2). Inasmuch as it requires from 7 t o 12 tons of wet waste t o yield 1 ton of dry pulp, from 1,190,000 t o 2,040,000 tons of the wet waste were utilized in this manner. Dried citrus pulp is also produced in the CaliforniaArizona area, but production figures are not available. The possibility of drying the waste and using it as a livestock feed was probably first suggested as far back as 1916 by McDermott, who a t that time held a Florida Citrus Exchange fellowship a t the Mellon Institute in Pittsburgh (21). I n 1927 the California Fruit Growers Exchange was drying orange pulp as a feed; dried grapefruit pulp was available in Florida about 1932, and in 1938 Texas was shipping it as far north as New England. The present method of drying the maste consists essentially of adding lime (0.3 t o 0.5%), shredding, aging in bins, pressing out
INDUSTRIAL AND ENGINEERING CHEMISTRY
477
Liquid Indicstrial Wastes part of t h e water by continuous presses, and then drying in either steam tube or direct-fired dryers. There is a great deal of variation in plant design and methods used: Some plants add dry lime, and others use a watery slurry; some operators add lime a t a constant rate, whereas others vary lime addition according t o the color changes in the aging pulp-lime mixture follon ing shiedding. I n some instances t h e limed pulp is aged in bins or pug mills for 45 t o 50 minutes, and in others aging is for less than 5 minutes. T h e pulp may or may not be preheated prior t o piessing, and in Texas the pulp is seldom, if ever, pressed. Retention time in the dryers varies from 10 minute.. t o as much as 2 hours or more, depending on the type used.
CITRUS PLANT PACKING 4,000 CASES N02'S PEA DAY(l0 HRS,)
1 Figure 3.
Schematic Diagram Showing Nature of Efflu-
ents from Citrus Cannery Packing Grapefruit Sections
and Juice
Dried citrus pulp contains about 6 % crude protein, 3y0 crude fat, 14 t o 15% crude fiber and from 53 t o 55% nitrogen-free extract. A more detailed analysis of grapefruit pulp is given in Table 11. T h e value of this material as a feed for dairy and beef cattle has been reviewed elsewhere (Sb'). It is quite likely that the drying of the solid citrus cannery waste for feed purposes will increase during the coming years. This prediction seems reasonable, based on the increased cattle production in the South Atlantic States (Tablc 111) and t h e present national emergency.
Liquid Effluents The most important of these effluents are from canning plants, from the drying of the pulp, and from plants producing chemicals from citrus (Table IV). Canning Plant Effluents. These effluents generally consist of ( a ) can-cooler overflow; ( b ) fruit-washing waste water; (c) peeling and sectionizing table waste water (only in plants packing sections or salads); ( d ) flushing water from floors, etc.; ( e ) water dripping from waste bins. The latter has a B.O.D. of about 50,600 p.p,m. and may amount to 28 gallons pel hour per bin (39). Waste alkali, encountered only in sectionizing plants, is usually dumped two or three times a meek. In soiiie instances the material is disposed of in dry wells, but it inay also be "bled" into other effluents from the plant. I n concentiate plants, wastes also include condenser cooling water. It has been estimated that such effluents amount t o 50 to 57 gallons per case of No. 2 cans packed (34). This is considerably greater than a report from Texas of 5.6 gallons per case of No. 2 cans (29). This is about the same as for lima beans and twice that for green beans, beets, corn, and peas. Composition of the effluent varies with the nat,ure of the pack. Figure 3 shows zt survey of a plant packing both sections and juice. Daily samples 478
(consisting of composites of hourly sample) of the effluent from this plant over approximately 6 months showed a 5-day B.O.D. from 100 t o 1400 p.p.m. (94). A similar study in the Rio Grande Valley of Texas showed a B.O.D. (computed) of 1160 p.p.m. for the effluent from a canning plant (26). Figure 3 s h o m that overflow water from the can cooler is used for fruit. washing and part of this combined waste water is pumped t o the peeling tables for flushing purposes. Thus, there is some attempt' t o reduce the volume of effluents from the plant.. Considerahle research has been done and is still being undertaken in the treatment of these cannery effluent.st o prevent public health nuisances and stream pollution. I n 1939, Rntcliff (17) reported that in Texas a reduction of 50 t'o 897, of the B.O.D. of cannery effluents could be obtained by screening, treatmeiit with a l u m and lime followed by dilution with cooling wash water containing no organic solids. About the same t h e the Texas %ate Department of Health reported similar results ( g 9 ) . Experinients with stone and sand filters indicated that rates as IOT as 1,000,000 gallons per acre per day tended t o develop septic conditions, reducing the effectiveness of the units. Bt the present time, the Texas State Health Department is continuing work in the valley on the use of chemicals and trickling filters in the treatment of citrus cannery effluent's. This xvork is being partly financed b y funds from the United States Public Health Seivice under the provisions of the Water Pollution Act passed b y t,he 80th Congress (90). Considerable experimentation was carried out in Florida from 1937 to 1940 by the Bureau of Agricultural and Indust,rial Chetnistry in cooperation Kith the Florida Canners Association and the Florida Stat,e Board of Health (34). The moat favorable results were obtained by a trickling filter which consisted of a concrete shell 8 feet deep, resting on suitable underpinnings for ready drainage and free circulation. The filter area amounted t o */gel of an acre, and was packed with so-called Florida flint rock ranging in size from 1 t o 3 inches. The distributor rotating a t about
Table 11. Analysis of Dried Grapefruit Waste (16) Moisture Bsh Protein ( N X 6.25) Crude fat Crude fiber Pentosans Sucrose (nonreducing sugars) Reducing sugars (as invert) Total sugars Pectin (alcohol precipitate)
Per Cent 7.54
Narinsin Potassium and sodium chlorides Silica Iron and aluminum (AlzOa FezOa) Magnesium (Mg) Calcium (Ca) Phosphates (PzOs) Sulfur (S) Chlorides (Clz)
6.00
6.49 5.46
14.06
+
14.35 9.18 2.82 11.00 18,ZO
Per Cent 1.52 1.79
0.23 1.94 0.34 1.63 0.26 0.10 0.05
Table 111. Cattle Production in South Atlantic States (31) No. Cattle (Thousands) 5527 5468 5848 6318
Year 1948 1949 1950
19
