Phosphate Release in Activated Sludge Process

The mechanisms of soluble phosphate uptake and release by the activated sludge process are the subject of considerable controversy. In this laboratory study, luxury uptake was clearly accomplished during substrate utilization. The extent of uptake varied directly with the initial phosphate concentration. The subsequent release of soluble phosphate under both aerobic conditions and anaerobic conditions varied directly with the extent of uptake. The release of phosphate under anaerobic conditions was inhibited by the addition of sulfate salts known to cause plasmolysis. Anoxic release was not a function of ORP change, but the extent of release may be a function of the initial ORP level. Anoxic release correlated well with the disappearance of DO from solution. However, the results of the entire study indicated that release is a function of the biological stress on the system, and that the magnitude of release is related to the stress magnitude. Soluble phosphate release from activated sludge was found to be biological in nature and primarily the result of cell lysis.