Treatment of household wastewater using an intermittently aerated membranebioreactor

An intermittently aerated membrane bioreactor using a submerged hollow fibe r membrane was applied in laboratory scale to treat household wastewater in cluding toilet flushing water. Nitrogen removal was optimized with intermit tent aeration of the reactor and adjusting the time lengths of anoxic and a erobic 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 ave rage, the removal efficiency for TN was 83%. No significant accumulation of inert matter was observed after 4 and 5 months of operations without sludg e wasting. Fast and complete nitrification was accomplished regardless of t he operation cycle mode, and denitrification appears to be the rate-limitin g step. Results from track studies revealed that the specific denitrificati on rate (SDNR) varied between 0.6 and 1.8 mg/gVSS h. Endogenous SDNR was de termined in a separate batch experiment and found to be 0.56 mg/gVSS.h. A l inear 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 a erated MBR appears to have advantages over other biological nitrogen remova l processes in that denitrification can be enhanced under high MLVSS condit ions. Endogenous denitrification may pray a significant role, making the sy stem more robust to the fluctuation or the limitation of external carbon su pply.