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 UV 254 removal efficiencies of the hybrid ozonation-coagulation (HOC) and pre-ozonation-coagulation (POC) processes for humic acid (HA) at pH 5 with AlCl 3 •6H 2 O as the coagulant. The DOC and UV 254 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 •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. [Display omitted] • HOC process has a wider ozone dosage range than pre-ozonation-coagulation process. • Ozone can react with hydrolysed Al species besides HA in the HOC process. • Ozone homogenizes the protonated groups of HA and hydrolysed coagulant species. • Simultaneous homogenization facilitates the binding between HA and coagulants. [ABSTRACT FROM AUTHOR]