Assessment of hydrogen peroxide, persulfate, and peroxymonosulfate as oxidizing agents in electrochemical oxidation of pyridine

Abstract

The removal of pyridine, a toxic and refractory nitrogen heterocyclic compound from coal chemical wastewater, has been examined using electrochemical oxidation (EO) processes in the presence of hydrogen peroxide (H₂O₂), persulfate (PDS), and peroxymonosulfate (PMS). Degradation of pyridine was observed in EO/H₂O₂, EO/PDS, and EO/PMS systems with removal efficiencies of 41.3, 40.6, and 93.5 %, respectively. The energy consumption for the EO/H₂O₂, EO/PDS, and EO/PMS processes was calculated to be 1.4, 1.3, and 0.56 KWh g⁻¹, respectively. The yield of ClO₃^- in the EO/PMS system was relatively higher than that in the EO/PDS system. Additionally, the overall concentration of total organic chlorine was lower in the EO/PDS (292.1 mg/L) and EO/PMS (120.1 mg/L) systems when SO₄•^– radicals were present. The contribution of reactive species were quantified. Specially, in the EO/H₂O₂ system, the ratio of OH• was 44 %. In the EO/PDS system, the ratios of OH•, SO₄•^–, and other reactive species were 31 %, 22 %, and 47 %, respectively. In the EO/PMS system, the ratios of OH•, SO₄•^–, and other reactive species were 18 %, 71 %, and 11 %, respectively. Specifically, in the EO/PMS system, while CCl₃ was detected, no other chlorinated organic intermediates were observed. Compared to EO/H₂O₂ and EO/PDS systems, the EO/PMS system shows better suitability for high Cl^– conditions. The pH had a negligible impact on the EO/H₂O₂ system. Under acid conditions, degradation rate constants for pyridine were highest in the EO/PMS and EO/PDS systems. Notably, the addition of PMS to coal chemical wastewater achieved a 30 % removal of ultraviolet light absorbance at 254 nm (UV₂₅₄), indicating effective inhibition of trihalomethane formation. This study provides critical insights into optimizing the EO process for the effective removal of refractory pollutants like pyridine from coal chemical wastewater, enhancing environmental safety and treatment efficiency.