Bisulfite triggers fast oxidation of organic pollutants by colloidal MnO.

Colloidal MnO is the most reactive phase of Mn(IV) while HSO is a common reductant in water treatment. This study shows that the presence of HSO resulted in significant increase in the decomposition rate of organic contaminants by colloidal MnO. The degradation rate of contaminants in the MnO/HSO process dropped with elevating pH and a proper MnO/HSO- molar ratio was critical for efficient decomposition of contaminants. The time-resolved spectroscopy of manganese species, the influence of pyrophosphate on UV absorbance spectra, and the relative rate constants of contaminants oxidation in MnO/HSO process suggested that the synergetic effect of HSO and colloidal MnO arose from the generation of Mn(III), which could oxidize contaminants rapidly. The presence of pyrophosphate, ethylenediaminetetraacetic acid, and humic acid depressed the degradation of contaminants in MnO/HSO process by complexing with Mn(III), buffering the solution or competing with contaminants for Mn(III), and/or inhibiting the consumption of bisulfite. However, Ca and Mg accelerated the oxidation of contaminants in MnO/HSO- process by enhancing the reduction of MnO by HSO-. The good negative correlation of the O/N or H Mulliken charges of organic contaminants with their removal in MnO/HSO process suggested that organic contaminants were oxidized by Mn(III) via electrophilic attack.