Rejection of trace level perfluorohexanoic acid (PFHxA) in pure water by loose nanofiltration membrane

Abstract

Recently, perfluorohexanoic acid (PFHxA), an emerging contaminant, has been detected at a high level in the water environment. Its possible presence in drinking water treatment process thus suggests that removal technique should be developed. In this study, one reverse osmosis (RO) membrane, two nanofiltration (NF) membranes and two ultrafiltration (UF) membranes were tested to reject PFHxA (100 - 300 ng/L) in pure water. The measured molecular weight cut-off (MWCO) of two NF membranes were as large as 10, 000 and 27, 000 Da, while they were still able to reject 96.3% and 95.3% PFHxA in pure water, respectively. This indicates PFHxA rejection rate was not dependent on the MWCO of membrane. Results also show that membrane with more negative zeta-potential tends to have higher rejection rate to PFHxA in pure water, suggesting that electrical repulsion between PFHxA and membrane might play an important role in PFHxA rejection. In conclusion, NF membranes would be a better option for removing PFHxA from drinking water than RO membrane because of their larger pure water permeability and NaCl transmission.