Osmotic membrane bioreactor for municipal wastewater treatment and the effects of silver nanoparticles on system performance

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-denaturing gradient gel electrophoresis (PCR-DGGE) analysis.