Inhibition of Perchlorate Formation during the Electrochemical Oxidation of Perfluoroalkyl Acid in Groundwater

Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS) are groundwater contaminants of emerging concern due to their toxicity and persistence. Currently, there are limited destructive treatment options for this type of water. One promising approach is electrochemical oxidation (EO) using a boron-doped diamond (BDD) anode. However, during EO treatment, chloride in water is readily converted to perchlorate (ClO4-), which is an endocrine disruptor. This is a common dilemma for EO techniques: anodes with higher EO activity tend to produce more ClO4-. In this study, we used the BDD anode as a model anode to treat PFOA and PFOS in a chloride-bearing electrolyte. We found that the formation of ClO4- can be largely inhibited without compromising the efficiency of PFOA and PFOS destruction by adding hydrogen peroxide (>= 50 mM H2O2). Experimental approaches and computational kinetic modeling indicate that H2O2 inhibits ClO4- formation by quenching chlorine and hydroxyl radicals and the oxidation of PFOA and PFOS is primarily determined by direct electron transfer oxidation, regardless of the dominant radical species. This facile strategy suppressed 88% of ClO4- formation during EO treatment of groundwater spiked with PFOA and PFOS.