Potable reuse with engineered osmosis; integrating an osmotic membrane bioreactor with membrane distillation.

A pilot-scale osmotic membrane bioreactor-membrane distillation (OMBR-MD) system was developed for potable wastewater reuse at military forward operating bases. The system consists of forward osmosis (FO) membranes submerged in a bioreactor and an MD system designed to reconcentrate the FO draw solution and generate product water using waste-heat. Prior to testing the pilot-scale system, two different FO membranes were compared at the bench-scale; there was no significant difference between thin-film composite and cellulose triacetate membrane performance. The OMBR subsystem had the same steady-state water flux with 20 and 35 g/L NaCl draw solution, although the 35 g/L draw solution increased bioreactor salinity. The bioreactor was operated with aerobic/anoxic cycling to achieve biological carbon and nitrogen removal in a single reactor. Long-term operation resulted in 98.4% COD removal and 90.2% NH4 plus minus N removal from high-strength wastewater. A novel dosing and transfer system was developed to maintain continuous water production and prevent heat transfer from MD to the OMBR, which is critical for biological nitrogen treatment.