A Three-electrode Electro-Fenton System Supplied by Self-generated Oxygen with Automatic pH-regulation for Groundwater Remediation

Abstract

The applications of electro-Fenton (E-Fenton) systems for groundwater remediation require effective O2 supply and pH adjustment in the aquifer. To avoid air sparging and achieve automatic pH regulation, we proposed a three-electrode E-Fenton system which utilized the electrochemically produced O2 from anodic oxygen evolution reaction (OER) and localized pH conditions near electrodes. In order to address the external demand of O2 for oxygen reduction reaction (ORR, two-electron transfer) compared to the O2 supply from OER (four-electron transfer) in the two-electrode system, an additional cathode (primary reaction as hydrogen evolution reaction, HER) was introduced to increase OER current for enhanced O2 production. With set current of −5mA for the additional cathode, the equivalent oxygen supply rate at the anode was 1.9mLh−1, resulting in a maximum H2O2 concentration of 20.9mgL−1 and Rhodamine B removal of 97.4% within 120min. The contaminant removal was much higher than that of 5.0% for two-electrode E-Fenton systems without aeration. Proton generation from the anode gradually developed the acidic environment (pH 2.9-3.1) in the treatment zone, which was beneficial for OH formation and contaminant removal. The aqueous pH was eventually neutralized by OH− produced from the cathodes, and the final pH was 6.1. Our system represents a promising approach for groundwater electrochemical remediation with efficient contaminant removal and pH regulations.