The canning industry uses an estimated 50 billion gal of water per year to process one billion cases of food. Liquid waste is normally screened as a first step in any treatment process. Solids from these screens can be trucked away as garbage or collected in a by-products recovery program.
Food product washing is the greatest source of liquid waste. The water used is normally reclaimed in a coun-terflow system, with a final discharge high in soluble organic matter and containing suspended solids—much of it inorganic—from the soil. Other wastes come from peeling operations. The amount of suspended matter varies with the type of peeling. The type of peeler—steam, lye, or abrasive—has an effect on the nature of the waste generated.
Normal practices utilize large volumes of water to wash away loosened peelings, creating tremendous suspended and organic loads in the waste stream. Lye peeling also generates wastewater with markedly high caustic alkaline concentrations. Equipment for dry lye peeling of fruits and vegetables removes the lye peelings in a semidry state so that solids can be handled separately without liquid contamination.
Raw foods are blanched to expel air and gases from vegetables; to whiten, soften, and precook beans and rice; to inactivate enzymes that cause undesirable flavor and color changes; and to prepare products for easy filling into cans. Little fresh water is added during blanching (8-hr shift), therefore the organic material concentration be comes high due to leaching of sugars, starches, and other soluble materials. Although low in volume, blanch water is highly concentrated and frequently represents the largest load of soluble wastes in the entire food processing operation. The amount of dissolved and colloidal organic matter varies, depending on the equipment used.
The last major source of liquid wastes is the washing of equipment, utensils, and cookers, as well as washing of floors and food preparation areas. This wastewater may contain a large concentration of caustic, increasing the pH above the level experienced during food processing.
After cooking, the cans are cooled, which requires a large volume of water. The cooling water is clean and warm and should be reused for washing.
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