Aerobic treatment of dairy wastes.

Abstract

Disposal of dairy wastes is of importance to all branches of the dairy industry, from the simple shipping and bottling of milk through the manufacture of milk products, including cheese, butter, ice cream, and processed milk. Drainage and washings are the main sources of wastes, with an occasional addition of surplus buttermilk, whey or spoiled materials. About 1 per cent of fluid milk entering a plant is lost even under good waste-preventing practices. Wash and cooling waters dilute this milk so that about 0.1 to 0.2 per cent milk solids is in the waste. This industrial waste with a 5-day biochemical oxygen demand (BOD) of 800 to 1500 parts per million (ppm) is a much stronger polluting agent than the same volume of domestic sewage with a BOD of about 200 ppm. Increasing demands for clean streams, failure of existing aeration systems to prevent odor and acid formation in dairy wastes, and the need for simplified small disposal systems induced the Dairy Industry Committee to present the problem to the Department of Agriculture. The low concentrations of solids in dairy waste does not warrant costly installation for anaerobic disposal. The relatively great oxygen demand, as well as the ready biochemical availability of the major constituents, lactose and protein, suggested studying an aeration treatment. Aerated or activated sludge processes for waste purification use microorganisms for the conversion of soluble oxygen-demanding organic materials to innocuous substances. Aerobic activities of the sludge microorganisms were investigated in these studies, in which a 0.1 per cent solution (1000 ppm) of dried skim milk was used as synthetic waste (table 1) having the