THE CASE FOR ANAEROBIC REDUCTION OF OXYGEN REQUIREMENTS IN BIOLOGICAL PHOSPHORUS REMOVAL SYSTEMS

Laboratory and pilot-plant scale studies were conducted to investigate the occurrence of anaerobic reduction of oxygen requirements in excess biological phosphorus removal (BPR) systems. The investigation was accomplished through application of chemical oxygen demand (COD)/oxygen-utilization mass balance techniques. Reductions of 0 to approximately 50% in the oxygen required for organic stabilization were achieved during treatment of synthetic and raw wastewaters. The reductions were attributed to stabilization occurring in the anaerobic reactors and represent a potential aeration energy savings that could be realized with BPR systems in addition to any savings associated with denitrification. Factors which influence the occurrence and magnitude of anaerobic stabilization include the composition of the influent wastewater, and the strength of the influent wastewater. It was concluded that substantial reduction of oxygen requirements can occur as a result of anaerobic stabilization and that the principal mechanism is probably metabolism by bacteria, such as fermenters, that do not accumulate phosphorus.