Chlorination of phenol, bisphenol A, and methylparaben in the presence of bromide: Kinetic simulation and formation of brominated aromatic byproducts

The seawater intrusion caused by the rising sea level increased the bromide (Br⁻) levels in the source waters of coastal cities. Adding bromide could significantly improve the degradation of phenol, bisphenol A, and methylparaben by chlorine. Bromide in water was first oxidized to active bromine species, which further reacted with phenols to generate brominated aromatic byproducts. A kinetic model including the reactions of chlorine oxidizing bromide, chlorine with phenol, and active bromine with phenol was established. The reaction rate constants of active bromine with phenols were calculated by fitting the degradation of phenols by chlorine in the presence of different bromide concentrations via the kinetic model. The rate constants of active bromine with phenols (1.5 × 10⁴ to 2.9 × 10⁴ M⁻¹s⁻¹ at pH 7.0) were higher than those of chlorine with phenols (4.0 × 10¹ to 8.9 × 10¹ M⁻¹s⁻¹ at pH 7.0), resulting in a bromide enhancement effect. The kinetic model could accurately simulate the evolution of total oxidant concentration with time (R² > 0.96). Various brominated aromatic byproducts were identified in the chlorine/phenols/bromide systems, and they were first produced and then further degraded by chlorine. The technology of removing bromide and phenolic components from source water should be developed to control the formation of toxic brominated aromatic byproducts.