The OMBR system comprised a rectangular tank with an operating volume of 5.034 L, and housing a flat-sheet cellulose triacetate. FO membrane module submerged in the tank. The effective area of the FO membrane module was 0.036m2. The bioreactor was aerated with an air pump (Hailea, China) through a straight rod air diffuser fixed directly below the membrane module. The bioreactor was initially filled with seed sludge from the aeration tank of a local pilot MBR plant in Singapore. Wastewater was fed into the bioreactor using a peristaltic pump. The operating volume in the bioreactor was maintained by a feed loop which provided a continuous flowof feed to the reactor. A schematic diagram is shown in Fig. 1.