Performance comparison of direct membrane separation and membrane bioreactor for domestic wastewater treatment and water reuse

Two pilot-scale wastewater treatment systems - direct membrane separation (DMS) and membrane bioreactor (MBR) systems - were designed and constructed in order to investigate the feasibility of membrane filtration technology for domestic wastewater treatment and water reuse. A submerged-type hollow-fiber microfiltration (HF-MF) membrane module with pore size of 0.1μm was employed to build each pilot system. The systems were tested using low- and high-strength domestic wastewaters and the system performance was continuously monitored for a long period to compare filtration characteristics and effluent quality in each system. The MBR system showed much better performance than the DMS system in terms of filtration characteristics and effluent quality. Even though the mixed-liquor suspended solid (MLSS) content in the MBR system was much higher than that in the DMS system, the MBR filtration resistance was much lower than the DMS filtration resistance. The DMS system was not able to remove dissolved organic matter, which seemed to be a major component of membrane fouling. The MBR effluent quality such as COD, BOD, TOC and T-N was more stable and better than the DMS. In the MBR process, the organic removal efficiency remained more than 95% regardless of fluctuation in influent qualities. The effluent quality of both systems was satisfying the legal standards for water reuse in Korea. Rejection of pathogenic microorganisms by membrane filtration was also investigated.