THE EFFECT OF AN INITIAL ANAEROBIC ZONE ON THE NUTRIENT REQUIREMENTS OF ACTIVATED SLUDGE

Laboratory-scale sequencing batch reactors operating on an acetate and casamino acids based synthetic wastewater were used to determine the phosphorus and nitrogen requirements of anaerobic/aerobic and completely aerobic activated sludge. At a 4 d mean cell residence time, anaerobic/aerobic activated sludge had an approx. 20% lower phosphorus requirement than completely aerobic activated sludge. The difference between the “end-of-aerobic cycle” polyhydroxybutyrate and carbohydrate contents of the sludges indicated that the anaerobic/aerobic sludge used more influent carbon than the completely aerobic sludge for synthesis of non-phosphorus-containing storage products. The limiting nitrogen requirements of anaerobic/aerobic sludge were similar to those of the completely aerobic sludge, but when nitrogen was in excess the completely aerobic system produced higher effluent soluble organic nitrogen concentrations. These findings are part of an evaluation of the suitability of the anaerobic/aerobic process for treating nutrient–deficient wastewaters in plants that have stringent effluent nutrient requirements.