Per- and polyfluoroalkyl substances (PFAS) at low concentration improve coagulation efficiency but induce higher membrane fouling in drinking water treatment

The presence of per- and polyfluoroalkyl substances (PFAS) in surface water has been widely reported in recent years. Many techniques, e.g., adsorption, have been investigated to remove PFAS from contaminated waters. However, the underlying impacts of PFAS on conventional drinking water treatment have been overlooked so far. In this study, we hypothesized whether PFAS have significant impacts on algae in surface water, which in turn may influence the performance of typical treatment processes (e.g., coagulation/membrane filtration). Therefore, we sampled a representative surface water (drinking water source) in Beijing, China, and dosed 2 representative PFAS compounds, at environment concentrations, to conduct bench-scale treatment tests. Results showed that the presence of PFAS caused larger flocs during coagulation and more severe ultrafiltration (UF) membrane fouling, compared with a control solution without PFAS. Specifically, PFAS at a low concentration (0.1 μg/L) led to the greatest influence on floc growth and UF membrane fouling; compared with the solution without PFAS, the floc size increased by 1.6 times and membrane flux declined more than 10%. These effects were evidenced by the stress response of algae under PFAS stimulus, secreting more biopolymers (mainly polysaccharides), rather than by PFAS directly. Overall, this study has demonstrated that the presence of PFAS can have both beneficial, and undesirable, indirect effects on water treatment in real applications, through its impact on algae in surface water sources.