Coupling electrode aeration and hydroxylamine for the enhanced Electro-Fenton degradation of organic contaminant: Improving H₂O₂ generation, Fe³⁺/Fe²⁺ cycle and N₂ selectivity

To improve H₂O₂ generation and Fe³⁺/Fe²⁺ cycle simultaneously for enhancing Electro-Fenton performance, the electrode aeration (EA) and hydroxylamine sulfate (HA) were coupled. With dimethyl phthalate (DMP) as main target contaminant, combination of HA and EA greatly accelerated the degradation of DMP and exhibited a synergy in the pH of 2.0–6.9 through promoting the key reactions, including electrochemical two-electron reduction of O₂ into H₂O₂ and redox cycles of Fe³⁺/Fe²⁺, which then improved the generation of hydroxyl radicals (·OH). The coupling EA and HA reduced the use of HA and converted most of HA into environment-friendly N₂ (60.1–62.1% of HA products), while HA/solution aeration(SA) system consumed HA rapidly and the generated N₂ only accounted for 5.8–6.7% of HA products. Furthermore, compared with HA/SA and EA Electro-Fenton systems, enhancement degree of DMP degradation in HA/EA Electro-Fenton process was higher in actual waterbody than in ultrapure water. The coupling EA and HA in the Electro-Fenton process could solve the low Fe³⁺/Fe²⁺ cycle efficiency and low H₂O₂ production simultaneously, and improve the N₂ selectivity of HA transformation, which advanced its application in practical environmental remediation.