Interactions between HO and dissolved organic matter during granular activated carbon-based residual HO quenching from the upstream UV/HO process.

Granular activated carbon (GAC) filtration can be employed to synchronously quench residual HO from the upstream UV/HO process and further degrade dissolved organic matter (DOM). In this study, rapid small-scale column tests (RSSCTs) were performed to clarify the mechanisms underlying the interactions between HO and DOM during the GAC-based HO quenching process. It was observed that GAC can catalytically decompose HO, with a long-lasting high efficiency (>80% for approximately 50,000 empty-bed volumes). DOM inhibited GAC-based HO quenching via a pore-blocking effect, especially at high concentrations (10 mg/L), with the adsorbed DOM molecules being oxidized by the continuously generated ·OH; this further deteriorated the HO quenching efficiency. In batch experiments, HO could enhance DOM adsorption by GAC; however, in RSSCTs, it deteriorated DOM removal. This observation could be attributed to the different ·OH exposure in these two systems. It was also observed that aging with HO and DOM altered the morphology, specific surface area, pore volume, and the surface functional groups of GAC, owing to the oxidation effect of HO and ·OH on the GAC surface as well as the effect of DOM. Additionally, the changes in the content of persistent free radicals in the GAC samples were insignificant following different aging processes. This work contributes to enhancing understanding regarding the UV/HO-GAC filtration scheme, and promoting the application in drinking water treatment.