Effect of COD/N ratio on nitrogen removal in a membrane-aerated biofilm reactor

• COD/N significantly impacted pollutant removal performance of MABR.
• MABR reactor presented good COD and nitrogen removal at a low influent COD/N of 5.
• Bacterial amount and density significantly declined at an influent COD/N of 3.

Efficient nitrogen removal for low COD/N wastewater is very important and membrane-aerated biofilm reactor (MABR) might be a solution. This study presented the performance of nitrogen removal in a MABR for wastewater with COD/N ratio from 10 to 3. The results indicated that the nitrogen removal in MABR was affected by the wastewater COD/N ratio but maintained high when the COD/N was 5 or higher. When the influent COD/N was 5, the COD, ammonium and total nitrogen removal efficiency reached 83.7%, 93.1% and 84.6% respectively. Meanwhile, the oxygen uptake rate of ammonia-oxidizing bacteria, nitrite-oxidizing bacteria and heterotrophic bacteria were 35.7, 46.7 and 25.7 mgO2/(gMLVSS·h), respectively. MABR had the advantage of high nitrogen removal efficiency at low wastewater COD/N than other bioreactors. Furthermore, PCR-DGGE was used to analyze the changes of amount and diversity of nitrogen removal bacteria with different COD/N ratios. Multiple bacteria related to biofilm formation, nitrification, denitrification and anaerobic ammonium oxidation processes were identified, and changed along with the change of COD/N ratio. The bacterial amount and density both declined significantly when the influent COD/N ratio was reduced to 3.