The mechanisms of self-inhibited reactions during hydroxyl radical-induced degradation of aniline disinfection by products

Abstract

Municipal wastewater post-treatment processes can effectively reduce the concentration of highly toxic disinfection by-products (DBPs) to minimize their ecological hazards. In this study, the reaction mechanisms and kinetics of 38 aniline disinfection by-products (AN-DBPs) degraded by ·OH in the post-treatment of municipal wastewater were investigated. Results showed that the apparent second-order reaction rate constants for the degradation of AN-DBPs by ·OH ranged from 1.25 × 10⁸ M⁻¹ s⁻¹ to 1.71 × 10¹⁰ M⁻¹ s⁻¹, and the products generated were mainly hydroxyl adducts (AN-OH) and AN-DBPs cation radicals (AN-DBPs⁺·). Based on the differences in the reduction potentials (ΔE_ox) of AN-DBPs and their degradation products, we proposed two self-inhibited reaction pathways in the degradation process. AN-OH and AN-DBPs can reduce AN-DBPs⁺· to the parent compound via single electron transfer reactions. AN-OH and AN-DBPs with fewer halogen atoms were more likely to inhibit AN-DBPs⁺·. It was noteworthy that self-inhibited reactions would occur when ·OH-dominated processes were used to degrade AN-DBPs. In addition, Cl^- in municipal wastewater usually has little effect on the self-inhibition efficiency, while the presence of Br^-, HCO₃^-, and NH₄⁺ usually promotes the self-inhibition reaction. These findings provide important theoretical insights for the effective removal of AN-DBP from water bodies.