Removal and recovery of perfluorooctanoate from wastewater by nanofiltration

Perfluorooctanoate (PFOA) is a persistent chemical that has been detected globally in the natural aquatic environment, while the waste discharge of fluoropolymer industry is one of the major sources of PFOA pollution. In this study, the removal and recovery of PFOA by nanofiltration (NF) were investigated with ammonium perfluorooctanoate model solutions under a wide range of PFOA concentrations. Performances of two commercially available NF membranes, namely NF270, NF90, were evaluated. The results show that the NF90 membrane offered a higher PFOA rejection (almost 100% at a PFOA concentration below 800 mg L−1). Using NF90 membrane, a model solution with a higher initial PFOA concentration of 1000 mg L−1 was used to further test the membrane performance. Both stable osmotic pressure at membrane surface and high PFOA rejection (99.3%) were obtained when the PFOA concentration was larger than a certain value due to the formation of micelles. Furthermore, membrane operation parameters (i.e. stirring speed, pH, temperature, and permeate flux) on the TMP and the PFOA concentration in permeate were investigated under a much higher initial PFOA concentration (10,000 mg L−1). The experimental results clearly confirm that recovery of highly concentrated PFOA of more than 117073.7 mg L−1 could be achieved by one-step NF treatment, while the permeate could be further treated by multi-stage NF to fully recover the PFOA. It was also found that the permeability of membrane could be recovered completely by simple water rinse, suggesting that NF is highly applicable for recovery of PFOA from wastewater in fluoropolymer production.