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Competitive kinetics and scavenging assay are commonly used for radical quantification. However, the accuracy of the two methods has been challenged in electrochemical advanced oxidation processes (EAOPs) since the strong reactivity of electrode against organic indicators may disrupt the quantitative relationship between indicator consumption and radical concentration. The present study focused on screening suitable indicators and developing suitable methods for determining the steady-state concentrations of SO 4 •- and HO • ([SO 4 •- ] ss and [HO • ] ss ) in several EAOPs for water treatment based on competitive kinetics and scavenging assay. The applicability of the modified methods and available indicators were investigated through experimental and kinetic analysis. In anode alone process, the competitive kinetics was more appropriate than scavenging assay and benzoic acid (BA) met the basic requirement of being a competitor to determine the [HO • ] ss . In cathode alone process, BA was more resistant to interfering factors than other competitors (ibuprofen, atrazine and nitrobenzene) and its reaction rate involved only the radical oxidation even when the reaction conditions varied over a wide range. Therefore, the [HO • ] ss could be obtained by the competitive kinetic equation of BA when HO • existed alone. When HO • coexisted with SO 4 •- , a two-step method combining scavenging assay and competitive kinetics was proposed to measure [SO 4 •- ] ss and [HO • ] ss , in which tert-butyl alcohol and BA were added as scavenger and competitor, respectively. Furthermore, the reliability of each approach was verified by the experimental results and kinetic analysis., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

To investigate the effect of cathode materials on organics degradation in a cathode/Fe 3+ /PMS process, different cathode materials (platinum, copper and iron) were selected and their performances were compared with iohexol as target organics. The optimal conditions were found to be different for different cathode/Fe 3+ /PMS processes. With a relatively high cathodic current input (2.0 mA/cm 2 ), similar results were found for all the three cathode/Fe 3+ /PMS processes. With a small cathodic current input (not higher than 1.0 mA/cm 2 ), the iohexol removal followed the order of Fe-cathode/Fe 3+ /PMS > Cu-cathode/Fe 3+ /PMS > Pt-cathode/Fe 3+ /PMS, due to the corrosion of Cu-cathode and Fe-cathode and the more serious corrosion of Fe-cathode than Cu-cathode. The corrosion of non-inert cathode materials (Cu-cathode and Fe-cathode) meant that these cathodes not only transmitted electrons but also participated in aqueous reactions, which complicated the mechanisms of cathode/Fe 3+ /PMS processes. The radical identification experiments indicated that SO 4 - was more important than OH for iohexol degradation in Cu-cathode/Fe 3+ /PMS process, while OH played a major role in Pt-cathode/Fe 3+ /PMS and Fe-cathode/Fe 3+ /PMS processes. The different reaction mechanisms resulted in different iohexol transformation pathways in cathode/Fe 3+ /PMS processes with different cathode materials., (Copyright © 2019 Elsevier Ltd. All rights reserved.)