Generation of chlorinated toxic by-products during phenol oxidation by persulfate: Species, toxicity assessments, and kinetic studies

Abstract

Persulfate (PS) advanced oxidation technologies are commonly used to remediate phenol-contaminated groundwater. However, the presence of chloride ions (Cl−) can lead to the generation of chlorine toxic by-products (Cl-TBPs), and the specific mechanisms of their generation are poorly understood. We investigated the quantity, type, and toxicity of Cl-TBPs associated with phenol and elucidated the generation trends and mechanisms of Cl-TBPs. Six types of Cl-TBPs with strong ecological toxicity were detected during phenol degradation. 2-chlorophenol (2-CP), 4-chlorophenol (4-CP), and 2,4-dichlorophenol (2,4-DCP) were present at high concentrations in the system. The elevation of temperature, PS, phenol, and Cl− concentration enhanced the generation of 2-CP, 4-CP, and 2,4-DCP, while HCO3− inhibited their generation. The concentrations of 2-CP and 4-CP initially increased and then decreased, with maximum concentrations of 57.6 μmol/L and 20.7 μmol/L, respectively. A total of 289 Cl-TBPs with high molecular weights were observed, with a molecular formula containing only CHO as the main component (85.8 %). The two chlorine-containing Cl-TBPs accounted for 75.9 % of the total Cl-TBPs, which consisted of highly unsaturated and aromatic compounds formed through addition reactions. This study provides a theoretical basis for revealing the generation mechanism of Cl-TBPs in the process of persulfate oxidation of groundwater.