Treatment of household wastewater using an intermittently aerated membrane bioreactor

An intermittently aerated membrane bioreactor using a submerged hollow fiber membrane was applied in laboratory scale to treat household wastewater including toilet flushing water. Nitrogen removal was optimized with intermittent aeration of the reactor and adjusting the time lengths of anoxic and aerobic phases of a cycle. Membrane filtration occurred during the aeration period to take advantage of the air bubbles for fouling control. With 8-15 h HRT and a very long SRT, 96% of TCOD and 100% SS could be removed. On average, the removal efficiency for TN was 83%. No significant accumulation of inert matter was observed after 4 and 5 months of operations without sludge wasting. Fast and complete nitrification was accomplished regardless of the operation cycle mode, and denitrification appears to be the rate-limiting step. Results from track studies revealed that the specific denitrification rate (SDNR) varied between 0.6 and 1.8 mg/gVSS·h. Endogenous SDNR was determined in a separate batch experiment and found to be 0.56 mg/gVSS·h. A linear relationship between the measured SDNR and the influent BOD/TN value was found. Based on this relationship, a rule-of-thumb method to determine the optimum time length for the anoxic phase was proposed. Intermittently aerated MBR appears to have advantages over other biological nitrogen removal processes in that denitrification can be enhanced under high MLVSS conditions. Endogenous denitrification may play a significant role, making the system more robust to the fluctuation or the limitation of external carbon supply.