Enhanced complexation of humic acids: Homogenization of protonated groups in the hybrid ozonation-coagulation process

In this study, we compared dissolved organic carbon (DOC) and UV254 removal efficiencies of the hybrid ozonation-coagulation (HOC) and pre-ozonation-coagulation (POC) processes for humic acid (HA) at pH 5 with AlCl3 center dot 6H(2)O as the coagulant. The DOC and UV254 removal efficiencies of the HOC process were higher than those of the POC process at ozone dosages less than 2.0 mg O-3 (mg DOC)(-1). The ozone dosage was optimized at 0.3 and 0.1 mg O-3 (mg DOC)(-1) for the HOC and POC processes, respectively, implying a more rigorous ozone dosage for the POC process. During the POC process, pre-ozonation was observed to increase the binding sites of HA (e.g., hydroxyl and carboxyl groups), improving the complexation of dissolved organic matter. For the HOC process, in addition to its role in the oxidation of organic matter, ozone also reacted with coagulants. The reaction between ozone and coagulants can facilitate the formation of Al-13. Moreover, the oxidation of center dot OH and ozone can increase the charge density of the HA binding sites, homogenizing the binding sites of HA and enhancing the complexation with Al-13. (C) 2021 Elsevier Ltd. All rights reserved.