Simultaneous removal of organic substances and nitrogen using a membrane bioreactor seeded with anaerobic granular sludge under oxygen-limited conditions

An innovative process, the oxygen-limited membrane bioreactor seeded with anaerobic granular sludge, was proposed and its performance investigated for concur-rent removal of organic substances and nitrogen from synthetic domestic wastewaters. An air diffuser was installed just above the granular sludge bed to supply air to the reactor at an intermittent mode. The internal recycle from the upper part of the reactor to the bottom was introduced to provide the granular sludge bed under the oxygen-limited conditions. The oxygen addition rates were controlled at 3-4 g O-2 l(-1)d(-1). The total COD removal efficiency of more than 94% was achieved throughout the whole operation period. N was removed through the simultaneous nitrification and denitrification process that took place in the granular sludge bed. TN levels decreased with the decrease of ammonium levels, indicating that nitrification was the rate-limiting step. The TN removal efficiency reached 80-91% at an hydraulic retention time of 15 h. Nitrate was scarcely detected and nitrite was the main NOx-N species in the effluent, indicating that nitrite oxidizers were inhibited in the system.