The effect of an initial anaerobic zone on the nutrient requirements of activated sludge

Laboratory-scale sequencing batch reactors (SBRs) operating on an acetate and casamino acids-based synthetic wastewater were used to determine the phosphorus and nitrogen requirements of anaerobic-aerobic (AnA) and completely aerobic (CA) activated sludge. At a 4-day mean cell residence time, AnA activated sludge had an approximately 20% lower phosphorus requirement than CA activated sludge. The difference between the "end-of-aerobic-cycle" polyhydroxyalkanoate (PHA) and carbohydrate contents of the sludges indicated that the AnA activated sludge used more influent carbon than the CA activated sludge for synthesis of non-phosphorus-containing storage products. Nitrogen requirement experiments showed that nitrogen limitations caused significant increases in the PHA and carbohydrate content of both the AnA and CA SBRs, and the limiting nitrogen requirements of AnA activated sludge were similar to those of the CA activated sludge. These findings are part of an evaluation of the AnA process for treating nutrient-deficient wastewaters in plants with stringent effluent nutrient requirements.