Amplified efficacy of short-chain perfluoroalkyl substances removal with nanofiltration-magnetic activated carbon integration

Abstract

In industrial wastewater treatment or reuse, managing short-chain perfluoroalkyl substances (PFASs) poses challenges when employing destructive methods due to their high bond energy. Chemical degradation and advanced oxidation processes often produce toxic intermediates. However, non-destructive methods, such as membrane filtration and carbon adsorption, offer promising alternatives. Here, we present a study on the effective control of two types of short-chain PFASs, namely perfluorohexanoic acid (PFHxA) and perfluoropentanoic acid (PFPeA), utilizing a non-destructive approach through a synergistic process involving nanofiltration (NF) and magnetic activated carbon (MAC). Firstly, a commercial hollow fiber NF membrane was employed to assess the removal efficiency of short-chain PFASs under optimal conditions, achieving 96.6 % removal for PFHxA and 86.1 % for PFPeA. Secondly, MAC was fabricated to compare its removal performance with powder activated carbon (PAC). MAC, offering recoverability and reusability post-saturation through regeneration processes, exhibited favorable characteristics over PAC. MAC with a uniform fine particle size prepared by ball milling was assessed through adsorption capacity experiments employing isotherm and kinetic analyses, confirming the adsorption efficiency of PFHxA (qe = 43.80 mg g−1) and PFPeA (qe = 32.70 mg g−1). Subsequently, a combined NF and MAC process was implemented to control PFHxA and PFPeA concentrations to part per trillion (ppt) levels. In this integrated approach, the initial feed solution permeated through the NF membrane, followed by MAC treatment, achieving concentrations as low as 50.6 ppt for PFHxA and 474 ppt for PFPeA. This study underscores the effective control of short-chain PFASs, aligning with increasingly stringent environmental regulatory standards.