This study reports the use of an osmotic membrane bioreactor (OMBR) for municipal wastewater treatment. The effects of silver nanoparticles (Ag-NPs) on the system performance were also examined. Using NaCl as the draw solution (DS) (at 49 g/L), a submerged OMBR system was developed and operated continuously for 108 days. Significant salt accumulation was observed at the beginning of the operation, which resulted in a mild deterioration in biological activity in the bioreactor, where NH4-N accumulated to around 10.0 mg/L in the first 15 days. However, the treatment efficiency recovered rapidly as the microbial community acclimatized to the elevated saline environment. Ag-NPs caused a significant decrease in nitrifying efficiency from 98% to 15% and an increase in the extracellular polymeric substances
(EPS) content in the activated sludge by 77.8%. A major shift in the bacterial community structure and decrease in community diversity was revealed in 16S rRNA gene based polymerase chain reaction edenaturing gradient gel electrophoresis (PCReDGGE) analysis.