An analysis on the fate of PFAS in still bottoms during electrochemical oxidation with a Ti4O7 anode

Most previous studies on the degradation of per- and polyfluoroalkyl substances (PFASs) by destruction technologies, such as electrochemical oxidation (EO), focused on the transformation of target PFASs, while a more complete analysis is necessary to verify PFAS mineralization and understand the pathways. This work attempts to analyze the fate of PFASs during EO treatment of still bottoms (SB), a concentrated waste stream resulting from ion exchange resin (IXR) treatment of PFAS-contaminated groundwater. The EO treatment is performed with a Ti 4 O 7 anode in a closed reactor in an attempt to analyze all products, including (1) their distribution in solid, liquid, and gas phases, (2) the fate of fluorine by quantifying both fluoride and total organic fluorine (TOF), and (3) semi-quantification of nontarget PFAS by high-resolution mass spectrometry. The results reveal that PFAS accounted for only 33% TOF in the original SB, with target PFAS responsible for merely 34% TOF removal by EO treatment, following which target and nontarget PFAS account for almost all TOF. Data suggest that most unaccounted TOF in the original SB was likely due to undetected PFAS masked by microplastics. Additionally, fluoropolymers may also be responsible. Most fluorine released from PFAS during EO treatment was recovered from the anode and precipitate. The study highlights challenges in tracking the fate of fluorine in destructive treatment of PFAS, especially regarding capturing volatile products in the context of complex environmental samples, while it showcases the capabilities of EO treatment in breaking down target and nontarget PFAS and their precursors.