Efficient COD removal and nitrification in an upflow microaerobic sludge blanket reactor for domestic wastewater

The treatment performance of an upflow microaerobic sludge blanket reactor (UMSB) for synthetic domestic wastewater was investigated at two dissolved oxygen (DO) levels, 0.3–0.5 and 0.7–0.9 mg l−1, focusing on nitrification performance. The higher DO level induced complete nitrification of ammonia nitrogen (NH3–N), achieving chemical oxygen demand and NH3–N removals of 97 and 92%, respectively. There were consistently significantly higher nitrate nitrogen (NO3–N) and nitrite nitrogen (NO2–N) levels in the effluent, with ~66% of newly-produced oxidised nitrogen as NO2–N. Despite the high nitrification efficiency, only about 23% of the removed NH3–N amount from the influent was ultimately transformed into oxidised nitrogen due to the simultaneous nitrification-denitrification. Sludge blanket development and granulation occurred simultaneously in the UMSB.