Pre-pilot forward osmosis – Membrane distillation hybrid system for sustainable produced water treatment and reducing volume of hazardous waste in oil and gas industry

This study introduces pre-pilot scale hybrid forward osmosis - membrane distillation (FO-MD) module, designed for the simultaneous treatment of different challenging produced water (PW) streams from Oil &Gas Industry. In this module, hot draw solution simultaneously serves as MD feed solution. The performance of this module was assessed with synthetic and real PW streams for extended operating times. The MD permeate production was doubled and comprised 0.4 L/h for 7:1 MD/FO area ratio (0.105 m² and 0.015 m², respectively) compared to permeate production that was observed with equal MD and FO membrane area (0.015 m² each). The conductivity of the final product water was 364.9 ± 2.7 μS/cm, comparable to the typical potable water conductivity, implying its potential for reuse applications and minimizing volume of hazardous waste. Analysis of MD permeate quality showed that concentration of major ions was reduced by >99 % and chemical oxygen demand was removed by 90.1 %. Continuous operation with real produced streams led to partial pore wetting on the MD active layer. The microscopy showed organic fouling caused by oil and grease deposition and NaCl/CaSO₄ scaling was found on both sides of FO membrane. These results suggest that PW pretreatment should be implemented to alleviate membrane fouling and pore wetting. We also observed reverse solute flux of 7.07 g/m² h in experiments utilizing real DE and WO streams. The results of this study helped to identify challenges arising from the system scale-up and provide grounds for integrating hybrid FO-MD technology to recover water from oil and gas facilities.