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

A high-efficient, eco-friendly and applicable oxidant of percarbonate (SPC, Na 2 CO 3 ·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 209.3 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 CO 3 2− could react with ·OH. Furtherly, the generation of hydroxyl radicals ( 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 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 .