Dopamine-functionalized PTFE membranes with enhanced flux and anti-fouling properties for membrane distillation of secondary effluent

Using secondary effluent from municipal wastewater treatment plants by membrane distillation (MD) to produce reclaimed water is an effective strategy for solving the growing global water shortage problems, however, membrane fouling caused by natural organic matter in the secondary effluent tends to reduce the water production rate of MD systems or destabilize these systems. Herein, the well-known dopamine (DA) surface functionalization method was applied and for the first time, DA-functionalized PTFE membranes (DA@PTFE) were fabricated to address the membrane fouling issue by treating secondary effluent enriched with effluent organic matter (EfOM) via direct contact membrane distillation (DCMD). The results showed that dopamine deposition formed a thin hydrophilic layer on the membrane surface, which inhibited the adhesion of contaminants and slowed down membrane fouling. The DA-9@PTFE membrane (with the C/F ratio of 1.25) demonstrated the best MD performance, with an increased flow rate of 13.8 % and much less membrane fouling compared with the pristine PTFE membrane (26.2 % vs. 56.8 % flux decay after three cycles). Meanwhile, using the DA@PTFE membranes in MD operation led to high water quality permeate, exhibiting a conductivity rejection rate above 99.6 % and a dissolved organic carbon retention rate above 90 %. This study demonstrates the good stability, wettability, and anti-pollution performance of DA@PTFE membranes in a DCMD system for real application in reclaimed water treatment.