Abstract
β-cyclocitral is a taste and odor (T&O) compounds and can cause malodorous problems in drinking water. This study focused on the kinetics and disinfection by-products (DBPs) formation of β-cyclocitral degradation by UV/persulfate (UV/PS) and UV/free chlorine processes. The degradation of β-cyclocitral in the two processes well fitted the first-order kinetic model. The second-order rate constant of β-cyclocitral with SO4·-, OH·, and Cl· were estimated to be (8.6 ± 0.12) × 109 M−1 s−1, (6.89 ± 0.42) × 109 M−1 s−1, and (9.58 ± 0.38) × 109 M−1 s−1 at pH 7.0, respectively. For UV/PS system, SO4·- contributed more than OH· does, while Cl· accounted for most degradation in UV/free chlorine process. The degradation rate increased with the increasing PS and chlorine dosage. For UV/PS process, the degradation rate constant (kobs,β-cyclocitral) was observed to be the highest at pH 7.0. For UV/free chlorine process, kobs,β-cyclocitral was found to be the highest at pH 5.0 and decreased substantially at pH 9.0. Presence of high concentration (5 mM) anions (chloride, bicarbonate) showed inhibition effect on the β-cyclocitral degradation. Dramatic decreasing was observed in the presence of NOM in both UV/PS and UV/free chlorine process. Compared with UV/PS system, UV/free chlorine was more suitable for treating waters containing β-cyclocitral because of the serious inhibition in real water matrix. UV/PS pretreatment reduced the trichlormethane (TCM) yield after post-chlorination, while enhanced the yield of dichloro acetaldehyde (DCAL). UV/free chlorine pretreatment promoted the formation of both TCM and DCAL. The theoretical cytotoxicity UV/PS pretreatment and post-chlorination is observed to be the highest due to the great amount of DCAL generation. Although UV/PS and UV/free chlorine processes can effectively degrade the β-cyclocitral, the selection of two processes should be carefully balanced against the DBPs formation in post-chlorination.
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