Abstract
In this study, we compared the decontamination kinetics of various target compounds and the oxidation by-products (bromate and chlorate) of PMS, PDS, and H2O2 under UV irradiation (UV/PMS, UV/PDS, UV/H2O2). Probes of different reactivity with hydroxyl and sulfate radicals, such as benzoic acid (BA), nitrobenzene (NB), and trichloromethane (TCM), were selected to compare the decontamination efficiency of the three oxidation systems. Experiments were performed under acidic, neutral, and alkaline pH conditions to obtain a full-scale comparison of UV/peroxides. Furthermore, the decontamination efficiency was also compared in the presence of common radical scavengers in water bodies [bicarbonate, carbonate, and natural organic matter (NOM)]. Finally, the formation of oxidation by-products, bromate, and chlorate, was also monitored in comparison in pure water and tap water. Results showed that UV/H2O2 showed higher decontamination efficiency than UV/PDS and UV/PMS for BA degradation while UV/H2O2 and UV/PMS showed better decontamination performance than UV/PDS for NB degradation under acidic and neutral conditions. UV/PMS was the most efficient among the three processes for BA and NB degradation under alkaline conditions, while UV/PDS was the most efficient for TCM degradation under all pH conditions. In pure water, both bromate and chlorate were formed in UV/PDS, small amounts of bromate and rare chlorate were observed in UV/PMS, and no detectable bromate and chlorate were formed in UV/H2O2. In tap water, no bromate and chlorate were detectable for all three systems.
Highlights
Sulfate radical (SO·4−)-based advanced oxidation process has attracted increasing attention as an alternative for traditional hydroxyl radical (HO·)-based advanced oxidation process, due to its high oxidation ability (Neta et al, 1988) and adjustability to generating HO· via pH manipulation (Guan et al, 2011)
Inorganic carbon (HCO−3 and CO23−) and natural organic matter (NOM) are widely present in surface water and groundwater, and regarded as free radical scavengers, leading to weakening the oxidation of target organic pollutants by advanced oxidation processes (Bennedsen et al, 2012)
HO· and SO·4− have different reactivity with inorganic and organic carbon, and the difference of reactivity would lead to a different effect on decontamination efficiency in HO· and SO·4−-based oxidation process
Summary
Sulfate radical (SO·4−)-based advanced oxidation process has attracted increasing attention as an alternative for traditional hydroxyl radical (HO·)-based advanced oxidation process, due to its high oxidation ability (redox potential of 2.5–3.1 V) (Neta et al, 1988) and adjustability to generating HO· via pH manipulation (Guan et al, 2011). UV/PDS showed a better performance than UV/H2O2 on the removal of carbamazepine (CBZ), 2,4-bromophenol, ofloxacin (OFX), ibuprofen, and cylindrospermopsin (CYN) (He et al, 2013; Yang et al, 2017; Sun et al, 2019; Luo et al, 2019; Xiao et al, 2020a). The better performance of UV/PDS on decontamination than UV/H2O2 was mainly ascribed to two factors: (1) the higher quantum yield of PDS ( = 0.7 mol Einstein−1) than that of H2O2 ( = 0.5 mol Einstein−1) and (2) lower steadystate concentration of HO· than SO·4− (Yang et al, 2017). UV/PDS showed higher removal efficiency than UV/PMS.
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