Nitrogen removal in household wastewater treatment using an intermittently aerated membrane bioreactor

Abstract

Membrane bioreactor using a submerged hollow fiber membrane was applied in laboratory scale conditions to treat household wastewater including toilet-flushing water. The bioreactor was aerated intermittently to alternate anoxic/oxic conditions while membrane filtration occurred during the aeration period to take advantage of the air bubbles for fouling control. After being operated for about 150 days, the initial flux and suction pressure were maintained almost constant at 0.01m hr(-1) and 4-6 kPa, respectively, indicating fouling control by air bubbling was very effective. With 10-15 hour hydraulic retention time (HRT), and a very long solid retention time (SRT), 97% of Total chemical oxygen demand (TCOD) and 100% suspended solids (SS) could be removed. On average, removal efficiencies for total nitrogen (TN) and total phosphorus (TP) were 83% and 55% respectively. Ammonia and coliform bacteria were completely removed. Due to the long SRT and sufficient oxygen supply, fast and complete nitrification was accomplished regardless of operational mode, and denitrification was the rate-limiting step. Results from track study revealed that the initial specific denitrification rate (SDNR) varied between 0.6 and 1.8 mg g(-1)VSS hr(-1). Endogenous SDNR was found to be 0.35-0.51 mg g(-1)VSS hr(-1). Nitrogen removal was controlled mainly by the value of BOD/TN of the influent. However, the role of endogenous denitrification was relatively significant under the high mixed Liquor volatile suspended solid (MLVSS) condition, making the system more robust to the fluctuation of external carbon supply. The anoxic/oxic cycle of 60/90 minutes with an hydraulic retentin time (HRT) of 10 hrs appears to be an appropriate choice for the process.