New insights on electrochemical remediation of soil/sediments: In situ phenol transformation and mineralization in spiked kaolin under low electric fields

Abstract

Most studies on electrochemical remediation of soil/sediment focus on the removal efficiency of one or more target organic contaminants without considering their evolution during the transformation and the possible release of other pollutants in the environment. In this study, the effect of electrochemical remediation (ER) of spiked kaolin on the transformation of phenol (PhOH) into many potential byproducts was investigated under very low electric fields (E). ER under 0.15 V cm− 1 was performed using cheap graphite electrodes in direct contact with the spiked kaolin with PhOH for 8, 24, 48, 96, 168 and 336 h. This study shows that the ER under low E value is an appropriate approach to concurrently desorb, mobilize and in-situ remove PhOH up to 70 % after 14 days, and for the first time, that PhOH in spiked kaolin is converted into several carboxylic acids (CAs), including maleic acid, formic acid and oxalic acids. They are simultaneously produced by PhOH oxidation and consumed by their following oxidation. Indeed, it was observed that the TOC/TOC◦ value decreases significantly to 38 ±10 % after 14 days, thus showing that an appreciable content of PhOH is converted to CO2 and water. This study points out that the ER process under very low E values might be an in situ viable way to oxidize hazardous organic contaminants into harmless compounds up to carbon dioxide and water without adding enhancing agents and at low energy consumption.