Simultaneous organic carbon and nitrogen removal by heterotrophic nitrifiers under oxygen-limited condition in an internal-loop fluidized membrane bioreactor

Abstract

An internal-loop fluidized membrane bioreactor (MBR) was operated to treat low-strength municipal wastewater by simultaneous removal of organic matter and nitrogen under oxygen-limited condition. Novel porous polymer carriers were used to immobilize microbes as well as alleviate membrane fouling. The dissolved oxygen (DO) concentration was varied from 0.07 to 0.5 mg/L at the top of the reactor throughout the experiment. The running conditions for the MBR were loading ammonia 50 mg/L, chemical oxygen demand (COD) 320 mg/L, hydraulic retention time (HRT) 8 h, pH 7.8–8.2, and C/N ratio 2.6. High removal percentages of COD, total nitrogen, and NH 4+ –N were achieved as high as 88%, 76%, and 96%, respectively, with only nitrite accumulated (10–13 mg/L) in effluent at optimal DO concentration of 0.12 ± 0.06 mg/L. With a membrane flux of 8 L/m 2 /h corresponding to 8 h HRT, transmembrane pressure remained below 20 KPa during 60 days of continuous operation without need for membrane chemical cleaning or backwashing. High-throughput sequencing analysis indicates that heterotrophic bacteria plays a significant role in nitrogen removal; Rhodobacter is the known heterotrophic nitrification–aerobic denitrification bacteria in the present system. In addition, the proliferation of filamentous bacteria in this system enhanced nitrogen and COD removal.