Removal of trace organic chemicals in wastewater effluent by UV/H2O2 and UV/PDS

Abstract

© 2018 Elsevier Ltd In this study, we comparatively investigated the degradation of 12 trace organic chemicals (TOrCs) during UV/H2O2 and UV/peroxydisulfate (PDS) processes. Second-order rate constants for the reactions of iopromide, phenytoin, caffeine, benzotriazole, and primidone with sulfate radical (SO4•-) were determined for the first time. Experiments were conducted in buffered pure water and wastewater effluent with spiked TOrCs. UV/PDS degraded all TOrCs more efficiently than UV/H2O2 in buffered pure water due to the higher yield of SO4•- than that of hydroxyl radical (•OH) at the same initial molar dose of PDS and H2O2, respectively. UV/PDS showed higher selectivity toward TOrCs removal than UV/H2O2 in wastewater effluent. Compounds with electron-rich moieties, such as diclofenac, venlafaxine, and metoprolol, were eliminated faster in UV/PDS whereas UV/H2O2 was more efficient in degrading compounds with lower reactivity to SO4•-. The fluence-based rate constants (kobs-UV/H2O2) of TOrCs in wastewater effluent linearly increased as a function of initial H2O2 dose during UV/H2O2, possibly due to the constant scavenging impact of the wastewater matrix on •OH. However, exponential increase of kobs-UV/PDS with increasing PDS dose was observed for most compounds during UV/PDS, suggesting the decreasing scavenging effect of the water matrix (electron-rich site of effluent organic matter (EfOM)) after initial depletion of SO4•- at low PDS dose. Fulvic and humic-like fluorophores appeared to be more persistent during UV/H2O2 compared to aromatic protein and soluble microbial product-like fluorophores. In contrast, UV/PDS efficiently degraded all identified fluorophores and showed less selectivity toward the fluorescent EfOM components. Removal pattern of TOrCs during pilot-scale UV/PDS was consistent with lab-scale experiments, however, overall removal rates were lower due to the presence of higher concentration of EfOM and nitrite.