Omniphobic membrane with process optimization for advancing flux and durability toward concentrating reverse-osmosis concentrated seawater with membrane distillation

Membrane distillation (MD) is an attractive desalination technology for further recovering highly concentrated brines with the advantages of high water recovery and salts rejection efficiency. However, advancing flux and tackling scaling of MD membrane are ongoing challenges due to the increasing temperature and concentration polarizations during the concentration process . Herein, we systematically investigated the membrane interface structure and common operating conditions on membrane flux and scaling resistance using reverse-osmosis concentrated seawater (ROCS) as a typical target. The results revealed that increasing membrane roughness, feed/permeate flow rate, and temperature gradient of membrane two surfaces could effectively improve membrane flux. Nevertheless, excessive feed/permeate flow rate and temperature gradient would accelerate membrane scaling due to enhanced disturbance to the membrane surface. The optimal membrane operated at a temperature gradient of 40 °C and a feed/permeate flow rate of 240 mL min −1 showed a high initial flux of ~48 L m −2  h −1 and an excellent water recovery ratio of 68.09% with the conductivity of distilled water lower than 11.72 μS cm −1 . In addition, the scaling resistance and flux of commercial antiscalants in ROCS on the differently wettable membrane interface were also systematically evaluated. These findings potentially transform MD to be a viable technology for concentrating ROCS using low-grade-thermal energy.