BIOLOGICAL PHOSPHORUS REMOVAL IN A MEMBRANE BIOREACTOR: A FEASIBILITY STUDY

Biological phosphorus removal (BPR) in an immersed membrane bioreactor is investigated, including anaerobic–aerobic batch tests for improved analysis of BPR activity. An IMBR pilot plant has been operated for combined nitrogen and biological phosphorus removal (BPR) from municipal wastewater at a sludge age of 25 days. COD and ammonia removal are not affected by strong disturbances and removal efficiencies remain at a continuously high level. BPR, however, is negatively influenced by the disturbances and displays a delayed start-up. Monitoring of the pilot plant reveals the feasibility of BPR in IMBRs, reaching removal performances of 80% for ortho-phosphate and 87% for total phosphate.Evaluation of batch test responses are used to reveal distinct differences during different operation periods. Anaerobic P-release rates, the ratio P-released / COD taken up and aerobic P-uptake rates are used to compare BPR activity between the individual batch tests. Sludge from the start-up phase and from the stabilized operation phase exhibit both the typical dynamic related to BPR (consumption of soluble COD with associated P-release). However, the calculated P-release rate differs, illustrating different degree of BPR expression.In a second step the parameters, mentioned above, are used to discuss potential differences compared to activated sludge systems.It is illustrated that BPR activity is expressed to a high extent in the IMBR pilot plant and that optimal BPR performance will most probably rely on the same influencing aspects as classical activated sludge systems. Optimization of operational conditions can, hence, be adapted from experiences with activated sludge systems, design for BPR.