Removal Of Phenolic Compounds By Al⁰/O₂System And The Effect Of Humic Acid

Phenolic compounds are a class of important environmental contaminants. It is important influence to ecosystem and human health. But the traditional wastewater treatments are difficult to remove completely phenolic compounds from environment due to its limitations. In this study, we used2,4-dichlorophenol and bisphenols A as model compounds to investigate the degration of phenolic compounds by Al°/O2system.(1) We investigated the oxidative removal of2,4-dichlorophenol by Al°/O2system. The results showed that more than90%of2,4-dichlorophenol was removed within10h in pH2.5solutions initially containing10.0g/L of Al and8.25mg/L of DO. A higher loading of Al accelerated removal of2,4-dichlorophenol.2,4-dichlorophenol removal in the Al°/O2system followed the order pH2.0> pH2.5> pH3.0> pH4.0. The reduction of oxygen to H2O2by Al could be only obtained under pH<4.0conditions. A higher level of oxygen and the presence of humic acid enhanced the generation of Reactive Oxygen Species (ROS) and the removal of2,4-dichlorophenol.The removal of2,4-dichlorophenol was resulted from its oxidation by the in situ generated hydroxyl radicals. The transformation of2,4-dichlorophenol was apparently accompanied by the release of chloride ions, suggesting the substitution of Cl atoms by other groups. In addition, five primary intermediate including4-chlorocatechol,2-chlorohydroqui-none,2-chloro-1,4-benzoquinone,4,6-dichlororesorcinol and3,5-dich-lorocatechol were identified and oxidation pathways of2,4-dichlorophenol by the Al°/O2system were proposed. This work offers an alternative for the removal of2,4-dichlorophenol in aqueous environments.(2) We investigated the effect of humic acid on the removal of bisphenols A by Al°/O2system under acidic conditions, especially the in situ generation of ROS in situ and the influencing of pH. About27.1%of bisphenols A was removed by Al°/O2system within10h in pH2.5solutions. And more than44%of bisphenols A was removed within10h after humic acid was added into Al°/O2system. Overall, humic acid enhanced the removal of bisphenols A by Al°/O2system. The addition of humic acid into Al°/O2system affected the formation of H2O2in situ and pH change. Results demonstrated that humic acid inhibited the formation of H2O2while facilitated the transformation of H2O2to·OH. HA displayed enhancing effects on bisphenols A removal by Al°/O2system when humic acid is added in the range of10.0-100.0mg/L.This work demonstrated that removal of phenolic compounds by Al°/O2system, the in situ generation of ROS and the influencing factorsor (example, pH, the initial dissolved oxygen and humic acid), offering a potentially practicable technology for treatment of phenolic compounds.