Enhanced removal of humic acid from aqueous solution by combined alternating current electrocoagulation and sulfate radical

Abstract

Application of alternating current in electrocoagulation and activation of persulfate (AEC-PS) for the effective removal of humic acid (HA) from aqueous solution was evaluated. In order to optimize the removal efficiency HA by the AEC-PS process, several influencing parameters such as pH, reaction time, PS dose, current density (CD), concentration of NaCl, initial concentration of HA, and coexisting cations and anions influence were investigated. From the batch experiments, the highest HA removal efficiency obtained was 99.4 +/- 0.5 at pH of 5, reaction time of 25 min, CD of 4.5 mA/cm(2), PS dose of 200 mg/L, and NaCl concentration of 0.75 g/L for an initial HA concentration of 30 mg/L. When CD increased from 1.25 to 4.5 mA/cm(2), the HA removal efficiency was improved from 88.8 +/- 4.4 to 96.1 +/- 1.5. In addition, the type of coexisting cations and anions exerted a significant role, leading to a reduction in the removal efficiency of HA. To investigate the dominant free activated radical, radical scavengers such as tert-butyl alcohol and ethanol were employed. It was observed that both center dot OH and SO4 center dot- radicals substantially contributed to the removal of HA, and the contribution of SO4 center dot- radical was higher than that of center dot OH radical, suggesting that AEC-PS process could serve as a novel and effective treatment technique for the removal of organic matters from aqueous sources. (C) 2021 Elsevier Ltd. All rights reserved.