Influence of aeration-induced air–water interfaces on pollutant degradation in water treatment: A theoretical and experimental study

Advanced oxidation processes (AOPs) based on hydroxyl radicals ([rad]OH)-dominant pathway are the most important technologies for the removal of bio-recalcitrant organic pollutants in industrial wastewater. Air–water interface formed by aeration is one of the factors that affect the removal efficiency of pollutants in AOPs. In this work, the mechanistic and kinetic insights into the roles of air–water interface on the hydroxylation of three chlorophenols (CPs) in UV/H₂O₂ process have been investigated via theoretical calculation and experimental methods. Results show that CPs is more prone to accumulate at the air–water interface as the number of chlorine substituents increases. Consequently, the hydration reaction of CPs occurring at the interfacial influence the electron transfer associated with [rad]OH, leading to the non-oxidative consumption of [rad]OH. This interfacial reaction diminishes degradation efficiency, resulting in the formation of persistent organic pollutants. Herein, in UV/H₂O₂ degradation of 2,4,6-TCPs, persistent free radical (PFRs), as well as 1,3,7,9-TCDD and 2,3,6-Trichloro-4-(2,4,6-trichlorophenoxy)phenol, were identified using EPR spectroscopy and LC-Q-TOF-MS mass spectrometry, respectively. Altogether, this work provides a comprehensive understanding of the roles of aeration on [rad]OH-initiated degradation behavior of chlorinated phenol pollutants.