Degradation of 2,6-dichloro-1,4-benzoquinone by UV/H2O2/O3 treatment: Effectiveness, water matrix effects, and degradation mechanism

• Published in: Chemosphere (Oxford) Vol. 296; p. 134014
• Main Authors: Pan, Zhangbin, Du, Zhenqi, Jia, Junqi, Lin, Aiguo, Wang, Yongqiang, Song, Wuchang, Sun, Shaohua, Wang, Hongbo, Jia, Ruibao, Hou, Lian
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.06.2022
• Subjects: 2,6-Dichloro-1,4-benzoquinone; Degradation paths; Influential factors; UV-AOPs; Degradation paths; 2,6-Dichloro-1,4-benzoquinone; Influential factors; UV-AOPs
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2022.134014

2,6-dichloro-1,4-benzoquinone (DCBQ), a typical representative of Halobenzoquinones, is an emerging aromatic disinfection by-product (DBP) with high toxicity and carcinogenicity, generated commonly through the chlorination in the drinking water disinfection process while there is still a lack of research on its removal. In this study, the effects of ultraviolet-based advanced oxidation processes (UV-AOPs) on the degradation of DCBQ were evaluated. The results showed that UV-AOPs are effective in degrading DCBQ. The removal of DCBQ by UV/H2O2/O3 was more significant than by UV/H2O2 or UV/O3, achieving a 96.7% removal rate at both the O3 and H2O2 doses of 1 mg/L. The results also indicated the alkaline and weakly acidic environments could facilitate the degradation of DCBQ, inorganic anions could inhibit DCBQ degradation and the degree of inhibition increased as the matrix concentration increased. The degradation of DCBQ was inhibited more by the CO32− than the other matrix components, such as Cl− and NO3−. It was shown by the density functional theory simulations and the ultrahigh-performance liquid chromatography (UPLC) - Orbitrap mass spectra that the electrons in DCBQ are mainly on the chlorine atom connected to the carboatomic ring and that OH• can attack the chlorine atom to cause de-chlorination. The DCBQ degradation pathway may involve the oxidation of DCBQ to 3-hydroxy-2,6-DCBQ (HO–DCBQ) and 3,5-dichloro-1,2,4-pyrogallol, the further degradation of intermediate products by OH• to dechlorinated forms of HO–DCBQ and DCBQ. [Display omitted] •UV/H2O2/O3 effectively degraded DCBQ with a removal efficiency of 96.7%.•OH.• and UV direct photolysis were main contributor to DCBQ degradation;•DCBQ degradation inhibited by Cl−, NO3−, HCO3− and CO32.•DCBQ was oxidized to generate dechlorinated HO-DCBQ and dechlorinated DCBQ.