Accelerated removal of organic pollutants by biochar-based iron carbon granule-activated periodate in chloride-containing water: The role of active chlorine

Ubiquitous in water environments, the chloride ion (Cl−) can impact the decontamination capacity of an oxidation system. However, minimal studies are available on its effects in periodate (PI)-based advanced oxidation processes. In this study, a novel biochar-based iron-carbon (FeBC) granule was synthesized to activate PI and remove organic pollutants from water containing Cl−. The FeBC/PI/Cl− system (FeBC: 0.5 g/L; PI: 0.5 mM; AO7: 20 mg/L; NaCl: 50 mM) exhibited excellent performance on various organic pollutants, with ˃ 85 % of Acid Orange (AO7) removal over a pH range of 3–10. Within 20 min after the tenth run, approximately 80 % of AO7 was removed. Inorganic ions and natural organic matter had a negligible effect on AO7 removal. Characterization results confirmed that the presence of Cl− enhanced Fe corrosion, thereby improving PI activation efficiency for removing AO7. Electron paramagnetic resonance spectroscopy and active species trapping experiments verified that radicals (•OH and O2•−) and nonradical (1O2, Fe(IV), and electron transfer) oxidation processes participated in the FeBC/PI system. Moreover, the presence of Cl− accelerated •OH, O2•−, 1O2, and Fe(IV) formation and generated active chlorine, such as HOCl. The main pathways involved in the generation of multiple reactive species were evaluated. AO7 degradation pathways were proposed, and numerous intermediates exhibited decreased toxicity. These findings provide new insights for the decontamination of organic contaminants in water containing Cl−.