The altered treatment efficiency of the bisulfite/permanganate process by chloride.

Bisulfite-activated permanganate (S(IV)/Mn(VII)) process has proven to be a promising method for rapidly degrading micropollutants. Previous studies have shown that the treatment efficiency of the S(IV)/Mn(VII) process suffer from significant water matrix effects while the mechanism still remains unclear. This study systematically investigates the influence of chloride, which is a common water constituent, on the S(IV)/Mn(VII) process. Addition of chloride decreased the removal of methyl phenyl sulfoxide, phenol, benzoic acid and carbamazepine by the S(IV)/Mn(VII) process but increased dimethoxybenzene removal. The distribution of reactive species in the S(IV)/Mn(VII) process in the absence and presence of chloride was determined with relative rate method. The S(IV)/Mn(VII) process primarily relies on SO4•- and reactive manganese species (RMnS) for pollutant abatement while dosing chloride decreased the concentration of these reactive species. Reactive chlorine species (RCS), such as Cl2•- and ClO•, are formed through the reaction of SO4•- with chloride, and become more important at high concentrations of chloride. RMnS includes Mn(VI), Mn(V) and Mn(III), but none of these species are capable of oxidizing chloride. However, chloride retarded the consumption of bisulfite which reduced RMnS and RCS in turn. DOM inhibited pollutant removal by the S(IV)/Mn(VII) process while the impact mechanism was significantly altered by chloride. Additionally, the study observed a synergistic inhibition of DOM and chloride on the degradation of pollutants that are highly reactive towards Cl2•- and ClO•.

Activation of Bisulfite with Pyrophosphate-Complexed Mn(III) for Fast Oxidation of Organic Pollutants.

Aqueous complexes of Mn(III) ion with ligands exist in various aquatic systems and many stages of water treatment works, while HSO3- is a common reductant in water treatment. This study discloses that their encounter results in a process that oxidizes organic contaminants rapidly. Pyrophosphate (PP, a nonredox active ligand) was used to prepare the Mn(III) solution. An approximate 71% removal of carbamazepine (CBZ) was achieved by the Mn(III)/HSO3- process at pH 7.0 within 20 s, while negligible CBZ was degraded by Mn(III) or HSO3- alone. The reactive species responsible for pollutant abatement in the Mn(III)/HSO3- process were SO4•- and HO•. The treatment efficiency of the Mn(III)/HSO3- process is highly related to the dosage of HSO3- because HSO3- acted as both the radical scavenger and precursor. The reaction of Mn(III) with HSO3- follows second-order reaction kinetics and the second-order rate constants ranged from 7.5 × 103 to 17 M-1 s-1 under the reaction conditions of this study, suggesting that the Mn(III)/HSO3- process is an effective process for producing SO4•-. The pH and PP:Mn(III) ratio affect the reactivity of Mn(III) towards HSO3-. The water background constituents, such as Cl- and dissolved organic matter, induce considerable loss of the treatment efficiency in different ways.