Removal of 4-chlorophenol, bisphenol A and nonylphenol mixtures by aqueous chlorination and formation of coupling products

Phenolic endocrine disrupting chemicals (EDCs) such as bisphenol A (BPA), 4-chlorophenol (4-CP) and nonylphenol (NP) are the most commonly detected pollutants in natural environments. The transformation of mixtures of the three phenolic pollutants during chlorination process was studied for the first time in this work. Single phenol can be effectively removed by free chlorine via electrophilic substitution and electron transfer reactions, with the generation of chlorinated phenols and self-coupling products. In mixture solution, the apparent second-order rate constants (kapp) of 4-CP, BPA and NP at pH 8.0 was increased by 8.6%, 25% and 16%, respectively, as compared to the degradation of single-compound. According to the products identification and density functional theory calculations, the cross-coupling process can occur more easily than the self-coupling reaction, which might accelerate the removal of phenolic mixtures. In addition, humic acid (HA) exerts some inhibitory effect on the degradation of phenolic compounds, due to the competition for chlorine consumption and the reduction of phenoxy radicals to parent phenols. These findings shed light on the environmental fate of phenolic mixtures during aqueous chlorination process, which provide new information for the application of chlorination in water and wastewater treatment.