Removal of trace organic chemicals in wastewater effluent by UV/H 2 O 2 and UV/PDS.

In this study, we comparatively investigated the degradation of 12 trace organic chemicals (TOrCs) during UV/HO and UV/peroxydisulfate (PDS) processes. Second-order rate constants for the reactions of iopromide, phenytoin, caffeine, benzotriazole, and primidone with sulfate radical (SO) 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/HO in buffered pure water due to the higher yield of SO than that of hydroxyl radical (OH) at the same initial molar dose of PDS and HO, respectively. UV/PDS showed higher selectivity toward TOrCs removal than UV/HO in wastewater effluent. Compounds with electron-rich moieties, such as diclofenac, venlafaxine, and metoprolol, were eliminated faster in UV/PDS whereas UV/HO was more efficient in degrading compounds with lower reactivity to SO. The fluence-based rate constants ( [Formula: see text] ) of TOrCs in wastewater effluent linearly increased as a function of initial HO dose during UV/HO, possibly due to the constant scavenging impact of the wastewater matrix on OH. However, exponential increase of k 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 SO at low PDS dose. Fulvic and humic-like fluorophores appeared to be more persistent during UV/HO 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.