Electrokinetically-delivered persulfate coupled with thermal conductive heating for remediation of petroleum hydrocarbons contaminated low permeability soil

In this study, electrokinetically-delivered persulfate (PS) coupled with thermal conductive heating (TCH) method was proposed for the remediation of petroleum hydrocarbons (PHs) contaminated low-permeability soil, based on the investigation of PS injection and activation by different electric field form, effective heating radius of TCH to activate PS, and their influencing factors. The uniform delivery and effective activation of PS were unrealizable by one-dimensional electric field (1 V/cm) with the operation of cathode injection, anode injection, bipolar injection, polarity-reversal, or bipolar injection coupled polarity-reversal, which would result in large spatial difference of soil pH and PHs residual. Similar results were obtained under the two-dimensional symmetric electric field (TEF) due to the large spatial difference in electric field intensity. Superimposed electric field (SEF, 1 V/cm) that based on the intermittent worked electrode groups coupled with polarity-reversal (every 3 h) and bipolar injection (10% PS solution) operation could achieve homogenized mass transfer of PS (53.8–65.7 g/kg, average 60.0 g/kg) in 15 days, due to the positive correlation between electric field intensity and transport of ionic substance. Meanwhile, the difference in decontamination efficiency caused by difference in PS activation efficiency could be reduced, since the heating rod was placed at the position where the concentrations of PS was the lowest, whereat the removal of PHs could not rely on alkali activated PS (cathode), anodic oxidation (anode), and electrochemical activated PS (cathode and anode). The residual concentration of PHs in soil remediated by SEF/PS-TCH was in the range of 640.7–763.8 mg/kg (average 701.5 mg/kg), and the corresponding removal efficiency was 73.3%–77.6% (average75.4%). The research can provide an in-situ remediation method for organic contaminants in low permeability soil featured with more uniform PS injection and activation, and small spatial differences in remediation efficiency.