Simultaneous electro-oxidation and in situ electro-peroxone process for the degradation of refractory organics in wastewater

Highlights: • Cathodic oxygen reduction reaction (ORR) is electro-catalyzed to produce H₂O₂. • In situ electro-peroxone is obtained in ORR electro-oxidation (EO) process. • Refractory organics is effectively removed by direct EO and in situ electro-peroxone. • ORR-EO also greatly reduces the energy consumption for organics removal. -- Abstract: During electro-oxidation (EO) wastewater treatment, the applied voltage must polarize both a dimensionally stable anode with a sufficiently high potential to effectively produce hydroxyl radicals (OH), as well as a cathode with a sufficiently low potential to catalyze the H₂ evolution reaction (HER). Nevertheless, H₂ does not contribute to pollutant degradation and yet increases energy consumption. Inspired by fuel cell technology, in which the O₂ reduction reaction (ORR) is catalyzed on the cathode, herein, a carbon nanotube-coated carbon-PTFE gas diffusion electrode was fabricated to catalyze ORR during EO for the treatment of leachate concentrates. In comparison to conventional HER-EO, ORR-EO was shown to save 17.7–23.2% energy consumption. Further, as the cathodic ORR byproduct, H₂O₂ can react with the ozone generated from the Ti/SnO₂-Sb₂O₅ anode to catalyze the peroxone process, which enhances OH generation for the degradation of organic products. This in situ electro-peroxone process was determined by salicylic acid OH trapping and liquid chromatography. The novel simultaneous EO and in situ electro-peroxone process described herein has great application potential and economic merit in the degradation of refractory organics in wastewater.