In this study, kinetics, influencing factors and potential mechanisms involved in the degradation of chloral hydrate (CH) by UV/peroxymonosulfate (PMS) process were demonstrated. The degradation rate of CH could reach 89.6% by UV 254 /PMS process, significantly exceeding UV 300 /PMS (0.7%), UV 350 /PMS (6.3%), UV 254 direct photolysis (9.0%) and PMS alone (0.0%) processes. CH degradation in UV 254 /PMS system followed pseudo first-order degradation kinetics with an apparent rate constant of 0.186 min −1 , which was suppressed by Cl − and HCO 3 − . The optimal pH for CH degradation was around 5.0. Direct mineralization accounted for the CH degradation in UV/PMS system. Interestingly, the addition of PMS at the neutral condition before UV irradiation transferred CH into trichloroacetic acid (TCAA). The transformation efficiency of CH into TCAA at 10 min was enhanced from 2.17%–40.38% with the elevation of initial pH from 7.0–8.0. The subsequent exposure of UV lamps ceased the transformation of CH into TCAA and facilitated the direct mineralization of CH, but it did not work in the refractory TCAA degradation. Finally, it was revealed that HO predominantly participated CH degradation in UV/PMS process, while O 2 − was responsible for the transformation of CH into TCAA by addition of PMS before UV irradiation.
Biological treatment is not completely effective for the removal of all refractory organics, including fulvic-like and humic-like substances, in fresh leachate from municipal solid waste (MSW) incineration. In this study, a UV/peroxymonosulfate (PMS) process was used to degrade the refractory pollutants that remained in the bio-treatment effluent. The reaction conditions were optimal when 10 g/L of PMS was used at a pH of 8.96. 70.6% of COD was degraded within 60 min with optimal reaction conditions. The refractory organics were degraded by the UV/PMS process, which generated intermediates with low molecular weight. The mechanisms involved in this advanced degradation process were uncovered by detecting the generation and conversion of radicals during the oxidation reaction.
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