Treatability Studies of Three Food Processing
Plant Wastewaters
C. FRED GURN.HAM, President
THOMAS K. NEDVED, Vice President
Gurnham and Associates, Inc.
Chicago, Illinois 60606
INTRODUCTION
The food processing industry is responsible for generating a large quantity of
predominately organic wastes. This industry is composed of an extremely wide variety of
plants (categories and subcategories in today's vernacular), including meat, fish, and
poultry processors; dairies and dairy product manufacturers; fruit and vegetable canners
and freezers; fermenters of malt, malt liquor, distilled spirits, and wines; beet and cane sugar
processors; edible oil refiners; and many others.
Wastewaters emanating from most food processing plants, although typically
approximately ten times the strength of raw municipal sewage, have usually proved
amenable to biological treatment processes with an appreciable degree of success. One
pollutant parameter, the so-called hexane-extractable material (HEM) has received
increasing attention. Fats, oils, and greases of animal and vegetable origin, present in bolh
domestic and food industry discharges, are reported by the analyst as HEM. This has
created a great deal of controversy and some consternation, as most experts want a test for
oily matter of petroleum origin. Some of the difficulties are attributable to the following: 1)
The non-specific nature of the "oil and grease" analysis; 2) The large number of materials, of
diverse nature, detected by the standard method; and 3) The errors and variations inherent
in both sampling and analytical procedures.
The analytical reference traditionally employed in water pollution control is Standard
Methods for the Examination of Water and Wastewater. The current 13th edition is divided
into six sections; the two sections of interest here are "Physical and Chemical Examination
of Natural and Treated Waters in the Absence of Gross Pollution" and "Physical, Chemical
and Bioassay Examination of Polluted Waters, Wastewaters, Effluents, Bottom Sediments,
and Sludges." Included in the first category are surface water, ground water, softened water,
cooling or circulating water, process water, boiler water, and boiler feed water. In the
second category are wastewaters of domestic and industrial origin, treatment plant
effluents, and polluted waters.
The 10th edition (1955) of Standard Methods described a direct extraction technique
for determining "oil and grease" in a 1,000-ml sample of natural or treated water water in
the absence of gross pollution; and a Soxhlet extraction technique for determining "grease"
in sewage, treatment plant effluents, polluted waters and industrial wastes, using a sample
containing from 50 to 150 mg of "grease." For industrial wastes high in "oils," a significantly
less accurate and tentative semi-wet extraction method was suggested. All three methods
used petroleum ether as the extracting solvent. Large sample sizes were required when
measuring low concentrations; this complicated the laboratory and pilot-scale studies.
The 11th edition (1960) added a Hydrocarbon and Fatty Matter Content of Grease
section and changed the extracting solvent to n-hexane (not hexanes) for sewage and
industrial wastes. Petroleum ether was retained as the extracting solvent in the water
chapter. No explanation was presented in the text for the changes.
The most recent edition (13th, 1971) is essentially the same as the 11 th in respect to oils
and grease except that an alternate extraction solvent, trichlorotrifluoroethane, can be used
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