Two stage intermittent aeration membrane bioreactor for simultaneous organic, nitrogen and phosphorus removal

A submerged membrane bioreactor (SMBR) was operated in 2-stage intermittent aeration for simultaneous removal of organic matter, nitrogen and phosphorus. The system consists of two reactors with a total volume of 0.27 m3 (1st reactor 0.09 m3 and 2nd 0.18 m3). Real domestic wastewater was used as influent to the system. Membrane used for this experiment was hollow fiber polyethylene membrane with pore size of 0.1μm and effective surface area, 4 m2. The membrane was submerged in the 2nd reactor for suction type filtration. Experiment was carried out in two phases varying the time cycles of aeration and non-aeration. SRT was maintained at 25 days and HRT, 16–19 hours. MLSS concentration in the reactors was in the range of 2,700–3,400 mg/l. The MLSS internal recycling ratio was maintained at 100% of influent flow rate. When time cycles of aeration and non-aeration were set at 30/90 min and 60/60 min in reactor 1 and 2, the removal of BOD and COD was 98.3% and 95.6%, respectively. A relatively low nitrogen and phosphorus removal was observed in this condition (73.6% as T–N and 46.6% as T–P). However, with 60/60 min intermittent aeration conditions for both reactors, the removal rate of nitrogen and phosphorus for two weeks steady state were enhanced to 91.6% as TN and 66% as TP, respectively. Further a high organic removal (98% BOD and 96.2% COD) was achieved too. In these conditions, the membrane of flux declined from 0.1 m/d to 0.08 m/d and suction filtration was at 10–12 kPa for a month long operation period.