RESPONSE OF DAIRY WASTE ACTIVATED SLUDGE TO EXPERIMENTAL CONDITIONS AFFECTING PH AND DISSOLVED OXYGEN CONCENTRATION

When activated sludge was fed a normal amount of artificial dairy waste, a sharp drop of pH and dissolved oxygen (DO) was observed immediately after feeding, due to the ready dissimilation of the carbohydrate fraction of the substrate. Decomposition of the protein fraction started later, proceeded at a much lower rate, and was accompanied by a slight fall of pH and DO for a more prolonged period of time. The drop of pH during dissimilation of the carbohydrate fraction was caused by a transitory occurrence of acid intermediates in the suspension. This was assumed to be due to the fact that, in spite of very vigorous aeration, the oxygen absorption rate was unable to meet the increased demand for oxygen and therefore the oxygen absorption rate became a limiting factor in the oxidation of the carbohydrate fraction of the substrate. The difference found between the dissimilation rate of the carbohydrate fraction and that of the protein fraction caused a discrepancy between the potential and actual C/N ratios of the substrate. Analyses of the acid intermediates showed that acetic acid was accumulated in the activated sludge suspension when DO was present, whereas lactic acid was found when DO was absent. © 1968.