Operational strategy preventing scaling and wetting in an intermittent membrane distillation process

Abstract The solar-powered membrane distillation (SPMD) process can improve the energy efficiency of the MD process by using solar energy as a heat source. However, the SPMD process can only be intermittently operated during the daytime. In this study, effects of intermittent modes (IMs) on scaling and wetting were investigated. Scaling and wetting tendencies in three types of shutdown protocols (P1: non-draining, P2: draining, P3: flushing and draining), IMs with/without temperature variations (IM-1/IM-2) and continuous mode (CM) were verified. A direct contact membrane distillation (DCMD) coupled with a real-time visualization system (in-situ method) and SEM-EDS (ex-situ method) were used for analysis in each condition. Consequently, scaling and wetting tendencies were lower in the P3 protocol, during which membrane samples were dried after drainage and flushing. Furthermore, scaling and wetting in CM and IM (IM-1 and IM-2) at P3 showed low differences, indicating that shutdown protocols had a more profound effect than temperature variations and operation mode. The visualization system provided information to understand and elucidate the mechanisms of scaling and wetting under each condition.