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

Abstract

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 (ClO 4 − ), which is an endocrine disruptor. This is a common dilemma for EO techniques: anodes with higher EO activity tend to produce more ClO 4 − . 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 ClO 4 − can be largely inhibited without compromising the efficiency of PFOA and PFOS destruction by adding hydrogen peroxide (≥50 mM H 2 O 2 ). Experimental approaches and computational kinetic modeling indicate that H 2 O 2 inhibits ClO 4− 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 ClO 4 − formation during EO treatment of groundwater spiked with PFOA and PFOS.

Electrosynthesis of >20 g/L H2O2 from Air

“…Benzoic acid (1 mM) was spiked in the catholyte as a radical probe. 33 , 34 No degradation of BA was observed throughout 135 min of electrolysis. Therefore, the conversion of H 2 O 2 to • OH was excluded, leaving the most plausible H 2 O 2 depletion mechanism as the cathodic reduction of H 2 O 2 by CB (H 2 O 2 + 2H + + 2e – → 2H 2 O; E 0 = 1.76 V).…”

Occurrence and removal of poly/perfluoroalkyl substances (PFAS) in municipal and industrial wastewater treatment plants

“…Both laboratory and pilot-scale studies show that this technology could be used for efficient degradation of PFAS-containing wastewater in full-scale, but more research should be conducted to determine optimum operating conditions and to provide a cost-effective process. Furthermore, the presence of chloride in wastewater may lead to the formation of toxic by-products, i.e., chlorate and perchlorate, during EOX treatment of PFAS (Yang et al 2019), and which should also be considered before using this technology.…”

Electrochemical technologies for per‐ and polyfluoroalkyl substances mitigation in drinking water and water treatment residuals

“…One limitation of these groundwater studies was that they employed relatively high PFAS concentrations compared to most drinking water sources and may not reflect the range of common PFAS contamination levels (e.g., <500 ng/L according to Glassmeyer et al (2017)). Yang et al (2019) used initial PFOA/PFOS concentrations of 10 μg/L (an order of magnitude lower than conditions tested in Schaefer et al (2017)) and found 90% PFOA and PFOS removal after 0.5 h of electrooxidation, which was far less treatment time than Trautman et al's (2015) 8 h of electrolysis for 50%–80% removal. Accordingly, more research is needed to determine PFAS treatability under low initial PFAS conditions (i.e., <500 ng/L) to determine the treatment inputs needed to meet potential PFAS regulations of <70 ng/L.…”

“…Removing precursor chloride can be accomplished by nanofiltration pretreatment to concentrate trace organics (e.g., PFAS) while excluding ionic species like chloride (Urtiaga, 2021). Yang et al (2019) determined that applying 50 mM H 2 O 2 successfully inhibited perchlorate production without decreasing PFAS treatment performance. The presence of 100–1000 mM methanol in ion exchange regenerant also decreased perchlorate formation during electrooxidation without compromising PFAS treatment performance (Wang et al, 2021).…”