Integration of forward osmosis with membrane distillation: effect of operating conditions

Hybrid desalination systems combining both thermal and membrane desalination processes are currently considered a viable alternative to conventional desalination plants. Recently, an incorporation of forward osmosis (FO) with membrane distillation (MD) has been considered as a new hybrid desalination technology. Nevertheless, few works have been done to design and optimize these types of new hybrid systems. The focus of this study was to investigate FO–MD hybrid process in which MD is being used to recover draw solutes in product water from FO. Laboratory-scale systems for FO and MD were developed to examine the effect of key operating conditions (draw solute concentration, operation time, temperature, etc.) on flux and solute transport. The results indicated that the efficiency of FO–MD hybrid is affected by the selectivity of draw solute transport through the MD membrane. As decreasing the temperature difference between the feed and distillate in MD, the rate of separation decreases but the selectivity increases. Based on these results, a simple model was proposed to analyze the efficiency of this FO–MD hybrid system.