Osmotically enhanced dewatering-reverse osmosis (OED-RO) hybrid system: Implications for shale gas produced water treatment

Managing shale gas produced water (SGPW) is one of the greatest challenges for shale gas industry due to its high salinity and water volume. Osmotically enhanced dewatering (OED) has great potential for treating SGPW because of its higher water recovery and lower energy consumption. This study systematically investigated the effects of operating conditions on OED performance through numerical simulation of membrane modules. The simulation results first showed that OED achieved higher water recovery over forward osmosis (FO) due to less internal concentration polarization (ICP). Water recovery could be higher with decreasing feed flow fraction, increasing normalized membrane area, and increasing hydraulic driving force fraction. It was also demonstrated that OED-RO hybrid process was able to yield more water with similar energy efficiency as one-stage RO, for SGPW of 28.5 g/L total dissolved solids (TDS) under realistic conditions considering inefficiency associated with pump and energy recovery device (ERD). Lastly, to validate our findings, OED experiments were performed with pre-treated real SGPW as a feed solution, and exhibited good agreement with the simulation results. Specifically, water recovery was achieved up to 67% with a high rejection rate of over 97% for most ions at a hydraulic pressure of 30 bar. Our modeled and experimental observations suggest that the OED-RO process can be an energy-efficient process in concentrating high salinity wastewater.