Electrooxidation of short- and long-chain perfluoroalkyl substances (PFASs) under different process conditions

Abstract

The electrochemical degradation of perfluorocarboxylic acids (PFCAs) and perfluorosulfonic acids (PFSAs) is examined using a Ti/RuO2 electrode. The effect of process parameters, such as type of electrolyte, electrode gap, current density, and initial PFAS concentration, is studied. The Ti/RuO2 anode shows better electrocatalytic performance with PFOS as compared to PFOA in the multi-compound system. However, the behavior differs in a single-compound system where higher PFOA degradation was observed. Intermediate products of PFOA and PFOS degradation is also reported indicating the formation of shorter chain compounds. The study reports on the degradation of short-chain PFASs (C < 7 for PFCAs and C < 6 for PFSAs) and long-chain PFASs (C ≥ 7 for PFCAs and C ≥ 6 for PFSAs). The PFAS chain length affects the degradation rate; the degradation ratios range between 16% and 67% for short-chain PFASs, and between 64% and 91% for long-chain PFASs. Different trends in reaction kinetics are also observed among the PFASs: while most of the PFASs showed pseudo-first order reaction kinetics, perfluoro pentanoic acid (PFPeA) and perfluoro nonanoic acid (PFNA) well-fitted to zero-order reaction kinetic; PFOS, perfluoro butanoic acid (PFBA), perfluoro dodecanoic acid (PFDoDA), and perfluoro octadecanoic acid (PFODA) displayed mixed pseudo-zero and first-order behavior.