Submerged versus side-stream osmotic membrane bioreactors using an outer-selective hollow fiber osmotic membrane for desalination

This study investigated the comparative performances, fouling mitigation efficiencies, and operational costs of side-stream and submerged osmotic membrane bioreactors (OMBR) systems using an outer-selective hollow fiber thin-film composite forward osmosis (OSHF TFC FO) membrane. Generally, the submerged OMBR system exhibited the higher fouling mitigation efficiency and a much slower flux decline rate when compared with that of the side-stream system. The side-stream OMBR system demonstrated an initial water flux of 15.8 LMH using 35 g/L NaCl as the draw solution, which was 2-fold higher than that of the submerged system when at its optimal performance. However, salinity accumulation in the reactor of the side-stream system was at a higher rate than for the submerged OMBR system. Both OMBR systems showed comparably high pollutant removal efficiencies over the experimental period. Annual operating costs for the side-stream OMBR system has been estimated to be 38% higher (OPEX) than for the submerged system. Membrane replacement cost accounted for the majority of the OPEX, over 89%, while the energy consumption and cleaning costs only accounted for relatively small portions. Therefore, reducing the membrane replacement cost is critical to realizing the commercial viability of the submerged OMBR system