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 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 flow of feed to the reactor. A schematic diagram is shown in Fig. 1.