Hsieh, M.-C.M.-C.HsiehPanchangam, S.C.S.C.PanchangamLai, W.W.-P.W.W.-P.LaiANGELA YU-CHEN LIN2020-02-252020-02-252018https://scholars.lib.ntu.edu.tw/handle/123456789/462688Free chlorine sunlight photolysis (sunlight/FC) markedly enhances the degradation rate of methadone, a synthetic opioid used medically, over that obtained using sunlight alone. The pseudo-first-order rate constants of methadone degradation under acidic conditions ([methadone] = 0.2 μM, [free chlorine] = 4 μM, and pH = 4) for sunlight/FC and sunlight photolysis are 7.0 ± 1.1 × 10−2 min−1 and 1.4 ± 0.2 × 10−2 min−1, respectively. The improved methadone degradation can be attributed to the production of HO[rad] and reactive chlorine species (RCS) during sunlight/FC photolysis. HO[rad] and RCS predominantly accounted for degradation during sunlight/FC photolysis under acidic and neutral conditions, while direct photolysis was the major contributor towards methadone degradation in alkaline conditions. The initial pH (pH 4–11) and free chlorine concentration (1–6 μM) significantly influenced the overall degradation efficiency of methadone. The presence of HCO3−, Cl− and dissolved organic matters, which may competitively react with HO[rad] and RCS, retard the degradation of methadone in synthetic wastewater. Consequently, a 50% lower methadone degradation rate was observed when deionized (DI) water was replaced with tap water. These results emphasize the need to consider different water matrices when applying sunlight/FC photolysis for water treatment. © 2018 Elsevier LtdFree chlorine sunlight photolysis; Hydroxyl radicals; Methadone; Reaction kinetics; Reactive chlorine species[SDGs]SDG6Alkalinity; Chlorine; Degradation; Deionized water; Free radical reactions; Photolysis; Rate constants; Reaction kinetics; Water treatment; Degradation efficiency; Dissolved organic matters; Free chlorine; Hydroxyl radicals; Methadone; Pseudo first order rate constants; Reactive chlorine species; Synthetic waste water; Photodegradation; anion; chlorine; dissolved organic matter; methadone; radical; reactive chlorine species; tap water; unclassified drug; chlorine; methadone; water; acidity; alkalinity; chemical compound; chlorine; concentration (composition); degradation; hydroxyl radical; matrix; photolysis; reaction kinetics; solar radiation; wastewater; wastewater treatment; water treatment; Article; degradation kinetics; effluent; pH; photolysis; sunlight; ultraviolet irradiation; waste water; waste water treatment plant; water treatment; chemistry; kinetics; photolysis; procedures; radiation response; water management; water pollutant; Chlorine; Kinetics; Methadone; Photolysis; Sunlight; Waste Water; Water; Water Pollutants, Chemical; Water Purificationjournal article10.1016/j.chemosphere.2018.06.0762-s2.0-85048553019https://www.scopus.com/inward/record.uri?eid=2-s2.0-85048553019&doi=10.1016%2fj.chemosphere.2018.06.076&partnerID=40&md5=aaca95108906e6df2ab57bfea5e21baa