A novel electro-Fenton process coupled with sulfite: Enhanced Fe³⁺ reduction and TOC removal

To promote the reduction of Fe³⁺ and improve the mineralization of organic pollutants, a novel electro-Fenton coupled with sulfite (Fe³⁺-EF/sulfite) process was constructed, which was superior to Fe³⁺-EF process in terms of carbamazepine (CBZ) degradation and mineralization with 5.99 times enhancement in degradation rate constant and 15.7 times enhancement on TOC removal. The complexation of Fe³⁺ and sulfite prevented the precipitation of Fe³⁺, reduced Fe³⁺ to Fe²⁺, and accelerated the iron cycle, so that H₂O₂ utilization efficiency (0.051 mg_TOC mg_H2O2^-1) was greatly improved and electric energy consumption was greatly reduced (0.081 kWh g^-1 TOC). The quenching experiments and EPR test confirmed that the reactive species, such as SO₃^•-, SO₄^•-, ^•OH, O₂^•- and ¹O₂ were responsible for the degradation of CBZ. This process also expanded the pH application range from 3 to 9 with satisfactory CBZ removal efficiency. This work verified the suitability of the Fe³⁺-EF/sulfite process for different sulfites (sulfite and bisulfite), typical pollutants (atrazine, sulfamethazine, rhodamine B) and real wastewater with 2.1-18.7 folds enhancement in degradation rate. The Fe³⁺-EF/sulfite process can achieve deep mineralization with low cost and simple operation, which has a broad and cost-effective application prospect in removal of refractory organic pollutants.