Enhancement effects of reducing agents on the degradation of tetrachloroethene in the Fe(II)/Fe(III) catalyzed percarbonate system

In this study, the effects of reducing agents on the degradation of tetrachloroethene (PCE) were investigated in the Fe(II)/Fe(III) catalyzed sodium percarbonate (SPC) system. The addition of reducing agents, including hydroxylamine hydrochloride, sodium sulfite, ascorbic acid and sodium ascorbate, accelerated the Fe(III)/Fe(II) redox cycle, leading to a relatively steady Fe(II) concentration and higher production of free radicals. This, in turn, resulted in enhanced PCE oxidation by SPC, with almost complete PCE removal obtained for appropriate Fe and SPC concentrations. The chemical probe tests, using nitrobenzene and carbon tetrachloride, demonstrated that HO was the predominant radical in the system and that O₂^- played a minor role, which was further confirmed by the results of electron spin resonance measurements. PCE degradation decreased significantly with the addition of isopropanol, a HO scavenger, supporting the hypothesis that HO was primarily responsible for PCE degradation. It is noteworthy that Cl^- release was slightly delayed in the first 20min, indicating that intermediate products were produced. However, these intermediates were further degraded, resulting in the complete conversion of PCE to CO₂. In conclusion, the use of reducing agents to enhance Fe(II)/Fe(III) catalyzed SPC oxidation appears to be a promising approach for the rapid degradation of organic contaminants in groundwater.