Performance of sweeping gas membrane distillation for treating produced water: Modeling and experiments.

Membrane distillation (MD) has shown promise for desalination of produced water (PW), but there are very few studies reported on the performance of MD with real PW and the characteristics of the fouling and scaling in MD. Among different MD configurations, sweeping gas MD (SGMD) is the least studied configuration. Here we report the application of SGMD for treating high-salinity PW (123 g L−1). The SGMD operating conditions were first carefully optimized through pure water MD experiments by varying operating conditions. The flux evaluation was accompanied by a detailed Aspen Custom Modeler simulation based on the electrolyte-NRTL thermodynamic model to better understand the heat and mass transfer in the feed and permeate channel. Supported by experiments, modeling results confirmed the partial condensation of the vapor in the permeate channel. Additionally, it was concluded that the saturation of the sweeping gas is controlling the overall mass transfer through the membrane. Selected membranes and optimized conditions were then used to conduct short-term and long-term performance tests with PW. In long-term MD test, the concentration of the PW increased by a factor of two (50% water recovery), while the membrane exhibited small flux decline. Elemental analysis showed that strontium and sodium were the major scalant compounds. • Aspen Custom Modeler (ACM) with e-NRTL thermodynamic model was used to predict the SGMD flux. • Modeling and experiments suggest that the sweep gas in the permeate side controls and limits the SGMD flux. • Produced water was concentrated to 250,000 mg L-1, and no membrane wetting was observed in long-term SGMD tests. • Characterization of the fouled and scaled membranes showed that organic matter can increase the possibility of membrane wetting. • Although at low concentration, strontium and iron were found to be the major scalants on the scaled membranes. [ABSTRACT FROM AUTHOR]