Abstract

A post-denitrification membrane bioreactor (MBR) system was developed to simultaneously remove organics and nitrogen from domestic wastewater. From a long-term experimental investigation, more than 96% organics could be degraded biologically and the effluent Chemical Oxygen Demand (COD) was below 10.5 mg/L. With a Hydraulic Retention Time (HRT) of 13.6 h and a total recirculation ratio of 8×Q, the MBR system could obtain a stably high Total Nitrogen (TN) removal efficiency of up to 92.4%, resulted in an effluent TN content of as low as 2.80 mg/L. Effects of operating parameters, including HRT, Sludge Retention Time (SRT), recirculation ratio and influent C/N, onto the system treatment performance were evaluated. It was revealed that HRT and recirculation ratio had significant impacts onto TN removal efficiency, reflected by that a reduced HRT to 9 h and a lower recirculation of 6×Q induced to 78.2% TN removal and an effluent TN of about 14 mg/L. A proper SRT and C/N ranged from 12 to 40 days, and from 8:1 to 13.5:1, respectively, have insignificant impacts onto the organic degradation and ammonia-N removal. Nevertheless, TN removal was highly inhibited by low SRT and C/N ratios. MBR combination with post-denitrification helps to enhance the organic and nitrogen removal compared with conventional activated sludge process, as it ensured a high biomass level in the treatment system.

Keywords: Biological nitrogen removal, membrane bioreactor (MBR), nitrogen gas, organic degradation, post-denitrification, wastewater treatment.