Highly efficient dual-cathode Electro-Fenton process without aeration at a wide pH range: Simultaneously enhancing Fe(II) regeneration and mineralization efficiency

Abstract

To simultaneously improve the H2O2 electrosynthesis, Fe(II) regeneration and pH application range in EF process, a highly efficient dual-cathode electro-Fenton (EF) process using easily available Fe(III) as catalysts for the treatment of organic wastewater at a wide pH range was first proposed, in which natural air diffusion electrode (NADE) was designed as one cathode for H2O2 production without aeration and the modified carbon felt (MCF) was acted as the other cathode mainly for Fe(II) regeneration. Nitric acid modification significantly enhanced the electrochemical properties of CF and introduced more oxygen-containing functional groups. The Fe(II) regeneration rate of MCF with higher electroactive surface area was 4.7 times that of CF cathode at pH 7. It was found that as the homogeneous Fe(III) was hydrolyzed into solid hydroxides, the accompanying H+ decreased the solution pH and MCF not only accelerated the dissolved Fe(III)/Fe(II) cycle but also reduced the adsorbed solid iron to ≡Fe(II) on the cathode surface. This simultaneously promoted the homogeneous and heterogeneous Fenton reactions and enhanced the efficiency of EF degradation process. For bronopol, 2,4-dichlorophenoxyacetic acid, sulfamethazine and phenol (100 mg L−1), the process had TOC removal of 48%−72% within 60 min with the corresponding mineralization current efficiency of 16.5%−56.2%, and the electrical energy consumption <0.225 kWh (gTOC) −1, which all greatly advantaged over that of the conventional EF. Therefore, this process is efficient and low-cost, being very promising for the treatment of organic wastewater.