Enhanced removal of coumarin by a novel O3/SPC system: Kinetic and mechanism

A high-efficient, eco-friendly and applicable oxidant of percarbonate (SPC, Na2CO3 center dot 1.5H(2)O(2)) is applied as oxidant in ozonation (O-3) process. In this work, coumarin (COU) decomposition by O-3 and O-3/SPC was proposed in terms of diverse parameters, including ozone concentration, SPC dosage and pH, with regard to the pseudo-first-order kinetic model. About 96.5% of 25 mg L-1 COU was removed by 2093 mg L-1 SPC and 2.08 mg L-1 O-3 within 30 min, whereas 49.8% of COU was exhausted in O-3 system alone. High ozone concentration and pH could enhance COU removal, and overdose SPC has an inhibition effect as CO32- could react with center dot OH. Furtherly, the generation of hydroxyl radicals (center dot OH) via a chain reaction in O-3 was ascertained based on indirect alcohols quenching tests and direct electron spin resonance (ESR) spin-trapping tests, though high initial SPC concentration led to no trapping of center dot OH by 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) in O-3/SPC. According to the concentration of dissolved ozone and prior study, a fast reaction kinetic model was estimated firstly for O-3/SPC system and well fitted with different condition. The hydroxylated intermediates of 7-hydroxylcoumarin and 6,7-hydroxylcoumarin were recognized and the degradation pathways were proposed. The findings of the study can broaden the research direction of SPC and provide a new application information for SPC in environmental pollution control. (C) 2018 Elsevier Ltd. All rights reserved.