Integrating an aerobic/anoxic osmotic membrane bioreactor with membrane distillation for potable reuse

A novel osmotic membrane bioreactor-membrane distillation (OMBR-MD) system was designed and fabricated to treat wastewater for potable reuse. Before longer-term operation to evaluate water flux and biological treatment of the pilot-scale OMBR subsystem, two forward osmosis (FO) membranes were evaluated at the bench-scale. There was no statistical difference between cellulose triacetate and thin-film composite membrane performance for activated sludge feed solution. Also, FO water flux during long-term operation was the same for 20 and 35 g/L NaCl draw solutions; however, the 35 g/L NaCl draw solution resulted in greater reverse salt flux and higher conductivity in the bioreactor. The OMBR subsystem was integrated with an MD subsystem to re concentrate the draw solution and produce high quality product water. Results from long-term testing using a high-strength wastewater showed 98.4% COD removal and 90.2% NH4+-N could be achieved with a single bioreactor by alternating aeration on/off cycles to control the redox environment. An automated dosing and transfer system was developed to maintain constant FO draw solution concentration and prevent heat from being transferred to the bioreactor, which is critical for maintaining biological nitrogen removal.