Desalinating microalgal-rich water via thermoresponsive membrane distillation

In this study, composite membranes for direct contact membrane distillation (DCMD) were fabricated by casting a top layer of PVDF that has blended with different dosages of thermoresponsive particles onto PTFE support. The fabricated composite membrane exhibits thermal-cleaning properties using pure water as a cleaning agent. The surface property and thermoresponsiveness of composite membranes were tested underwater at both room and elevated temperature (60 °C). The fouling tendency and cleaning efficiencies of composite membranes were evaluated using model foulants namely bovine serum albumin (BSA) and sodium alginate (SA). Membranes dosed in with poly(N-isopropylacrylamide) (PNIPAM) showed both hydrophobic and oleophobic properties under elevated temperature (60 °C). This makes it suitable to be used for membrane distillation (MD) operation. It was found that composite membranes with 1.0% PNIPAM showed excellent cleaning efficiency with flux recovery of 88.26% after microalgae fouling. Hence, the swelling and shrinking of PNIPAM in composite membrane that create surface actuation force during membrane thermal cleaning was able to repel the algal organic matter (AOM) that fouled on membrane surface. Besides, the rehydrated PNIPAM could repel the foulants that interacted with hydrophobic interaction during cold water washing.