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Hydroxyl radicals (HO·) show low reactivity with perchlorinated hydrocarbons,such as carbon tetrachloride (CT),in conventional Fenton reactions,therefore,the generation ofreductive radicals has attracted increasing attention.This study investigated the enhancement of CT degradation by the synergistic effects of hydroxylamine (HA) and formic acid (FA) (initial[CT]=0.13 mmol/L) in a Fe (Ⅱ) activated calcium peroxide (CP) Fenton process.CT degradation increased from 56.6％ to 99.9％ with the addition of 0.78 mmol/L HA to the CP/Fe(Ⅱ)/FA/CT process in a molar ratio of 12/6/12/1.The results also showed that the presence of HA enhanced the regeneration of Fe(Ⅱ) from Fe(Ⅲ),and the production of HO· increased one-fold when employing benzoic acid as the HO· probe.Additionally,FA slightly improves the production of HO·.A study of the mechanism confirmed that the carbon dioxide radical (CO2·),a strong reductant generated by the reaction between FA and HO·,was the dominant radical responsible for CT degradation.Almost complete CT dechlorination was achieved in the process.The presence of humic acid and chloride ion slightly decreased CT removal,while high doses of bicarbonate and high pH inhibited CT degradation.This study helps us to better understand the synergistic roles of FA and HA for HO· and CO2·-generation and the removal of perchlorinated hydrocarbons in modified Fenton systems.