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

The applications of electro-Fenton (E-Fenton) systems for groundwater remediation require effective O-2 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 O-2 from anodic oxygen evolution reaction (OER) and localized pH conditions near electrodes. In order to address the external demand of O-2 for oxygen reduction reaction (ORR, two-electron transfer) compared to the O-2 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 O-2 production. With set current of -5 mA for the additional cathode, the equivalent oxygen supply rate at the anode was 1.9 mL h(-1), resulting in a maximum H2O2 concentration of 20.9 mg L-1 and Rhodamine B removal of 97.4% within 120 min. The contaminant removal was much higher than that of 5.0% for twoelectrode 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)-O-center dot 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. (C)2017 Elsevier Ltd. All rights reserved.