Chloride-enhanced degradation of micropollutants in natural water by the iron/biochar/peroxymonosulfate system: Role of iron(IV) and radicals

The increased occurrence and concentration of micropollutants in water supplies raise public health concerns. Advanced oxidation of micropollutants in real water sources remains challenging due to scavenging reactions involving background anions and natural organic matter. For the first time, this paper demonstrates that chloride (Cl^-) accelerates the activation of peroxymonosulfate (PMS) by iron-biochar (Fe/BC) composites. Under the tested conditions, this novel system completely degraded bisphenol A (BPA), a representative micropollutant, within 1.0 min. Micropollutant degradation was investigated at different Cl^- contents, PMS levels, Fe/BC doses, and solution pH. The primary reactive species involved with BPA degradation were iron(IV) (Fe(IV)), sulfate radical (SO₄^•-), hydroxyl radical (^•OH), and reactive chlorine species (Cl^•, ClO^•, Cl₂^•-). The steady-state concentrations of these reactive species were evaluated to determine their relationships to the Cl^- and PMS contents. Fe(IV) was confirmed as the dominant reactive species, with Fe(IV) concentrations increasing with Cl^- content and salinity to enhance the overall BPA degradation. Importantly, BPA degradation by the Fe/BC/PMS/Cl^- system was not greatly affected by background anions or natural organic matter (NOM) present in real water sources, and the system was successfully applied for five sequential cycles of BPA treatment.