Investigation of nitrogen removal performance with membrane sequencing batch reactor process

Nitrogen removal performance was investigated using synthetic wastewater as feed without sludge discharge in an anaerobic/aerobic membrane sequencing batch reactor (MSBR) during 300 days operation. The results showed that MLSS in reactor was retained up to about 18 g·L-1, sludge size larger than 100 μm was 96%, and aerobic granular sludge was developed. The bacterial community observation of AOB and NOB by FISH-CLSM for sludge revealed that they were existed in larger numbers. When influent NH+4-N concentration was about 50 mg·L-1, effluent NH+4-N concentration was lower than to 1 mg·L-1, and nitrification could complete in 180-210 min. There was a good correlation between nitrification reaction and aeration strength. When aeration strength was 100 m3·(m2·h)-1, NH+4-N degradation rate 24.25 mg·(L·h)-1, and nitrification reaction in MSBR was stable. The main factor determining nitrogen removal of the system was denitrification rate, which was optimal at aeration 69 m3·(m2·h)-1, when the nitrification rate of NO-3-N 10.98 mg·(L·h)-1, effluent NO-3-N 4.4 mg·L-1, and NO-3-N in the beginning of anaerobic phase 3.5 mg·L-1. The denitrification performance was not benefited by excessive aeration or deficient aeration. Bigger volumetric exchange ratio was helpful for nitrogen removal and the system treatment capacity. The C/N ratio 2 was suitable to good denitrification rate, while there was a NO-2-N accumulation if C/N ratio was larger than 2.