Effect of variable influent loading on biological phosphorus removal

Biological phosphorus (bio-P) removal processes are receiving increased attention as the costs and sludge disposal problems associated with traditional metal precipitation become of greater concern to system designers and operators. Biological processes, however, have not demonstrated the same ability as chemical processes to consistently produce effluents low in total phosphorus. The results of this investigation indicate that the dynamic biochemical oxygen demand (BOD) and phosphorus loading patterns observed at full-scale systems can impose varying degrees of stress on bio-P removal processes. Increases in the amount of loading-related stress on bench-scale bio-P systems are manifested by increases in long-term average effluent phosphorus concentrations. Effluent variability is magnified when activated sludge systems are operated for both nitrogen and phosphorus removal. Mitigating measures can be employed to improve long-term process performance, but at the cost of increased system complexity and increased sludge production.