Effect of DO on simultaneous removal of carbon and nitrogen by a membrane aerated bioreactor

In order to achieve an optimum DO for simultaneous carbon and nitrogen removal by the Membrane Aerated Bioreactor(MABR)treating wastewater, a MABR in which the hydrophilic polypropylene hollow-fiber membrane module was used was constructed, and the effect of DO on simultaneous removal of carbon and nitrogen by MABR treating synthetic wastewater was investigated during the 80 days' continuous operation. The results show that under the relative stable condition that hydraulic retention time(HRT)was 8 h, and the membrane surface loading rate was 3.7 g·m^-2·h^-1(COD)or 0.36 g·m^-2·h^-1(TN), MABR realized preferable simultaneous removal of carbon and nitrogen when DO was 0.5 mg/L around. The removal rate of COD, NH₄⁺-N and TN was 80%, 86.4% and 66.5%, respectively. When DO was 4 mg/L or 2 mg/L around, both COD and NH₄⁺-N removal rate rose to more than 88%, but denitrification was limited, which resulted in a poor TN removal, with the former TN removal rate being 10% and the latter 24%. When DO dropped to 0.1 mg/L around, COD and NH₄⁺-N removal rate decreased to 60% and 57.4%, respectively, and TN removal rate also decreased to 46.8%. It was suggested that DO in the mixed liquor of MABR should be controlled at 0.5 mg/L around for an effective simultaneous carbon and nitrogen removal.