Enhanced trichloroethene degradation performance in innovative nanoscale CaO2 coupled with bisulfite system and mechanism investigation

Abstract

• HSO 3 – significantly enhanced HO• generation and TCE degradation. • HO• was the dominant ROSs in nCaO 2 /Fe(III)/HSO 3 – system. • The double effect of CaO 2 as both oxidant and O 2 source was clarified. • The enhancement mechanism caused by HSO 3 – was revealed. The effect of bisulfite (HSO 3 – ) in nCaO 2 /Fe(III)/HSO 3 – system on improving HO• generation and trichloroethene (TCE) removal was innovatively reported. The enhancement mechanism of HSO 3 – for TCE removal in nCaO 2 /Fe(III)/HSO 3 – system was caused not only by the complexing and reducing effects on promoting the conversion of Fe(III) to Fe(II), but also due to the reaction with O 2 in water to produce SO 4 – • for accelerating TCE degradation. A double effect of nCaO 2 as an oxidant source to generate HO• and as a O 2 source to promote SO 4 – • generation was revealed. A pseudo-second-order kinetic model of TCE removal was determined and 94.6% TCE degradation was achieved within 60 min at the nCaO 2 /Fe(III)/HSO 3 – /TCE molar ratio of 6/12/9/1, in which 82.8% TCE was dechlorinated. The scavenger test and EPR detection found that various kinds of reactive oxygen species (ROSs) including HO•, SO 4 – •, O 2 – • and 1 O 2 were generated, all contributed to TCE removal and HO• was the dominant one in nCaO 2 /Fe(III)/HSO 3 – system. The effects of surfactant presence and the complex matrix in the actual groundwater were evaluated. The experiments of high efficiency for chlorinated olefins and benzene series removals but low applicability for chlorinated alkanes provided an alternative technique to remedy groundwater based on the various kinds of contaminants performance.