A microaerobic membrane bioreactor seeded with anaerobic granules for domestic wastewater treatment

The performance of an innovative process, microaerobic membrane bioreactor seeded with anaerobic granular sludge was investigated for concurrent removal of organic substances and nitrogen from the synthetic domestic wastewaters. The total COD removal efficiency of more than 93% was achieved, unaffected by the changes in influent COD and HRT throughout the whole operation time, Nitrogen was removed through the simultaneous nitrification and denitrification process. The N-removal rate of the system was 20-45 mg N L-1d-1 at the nitrogen-loading rate of 26-67 mg N L(-1)d(-1). Nitrification was the rate-limiting step. The average TN removal efficiency increased from 77% at the COD/TN ratio of 19.5 to 87% at the ratio of 7.7. The batch test with granules can achieve 92% COD removal and 84% TN removal, whereas the COD and TN removal declined to only 84% and 67% respectively after the granules was homogenized. The SEM observation revealed that there were fluffy voluminous biolayers on the microaerobic granule surface. No marked difference in microbial composition of the cross-sectioned granules was observed between the two types of granules.