Accelerated degradation of pesticide by permanganate oxidation: A comparison of organic and inorganic activations

Permanganate (PM) is a widely-used oxidant in water treatment. However, the oxidation rate of micro-pollutants by PM is highly variable, dependent on the electron density of certain moieties of micro-pollutants. Using a pesticide (carbendazim, CBZ) as a target micro-pollutant, this study compared the organic and inorganic activations of PM by benzoquinone (PM/BQ) and bisulfite (PM/BS), respectively. It was found that both the PM/BQ and PM/BS systems could accelerate the degradation of CBZ with different degradation rates. The PM/BS system completed the degradation of CBZ (96.6%) within 15 s, while the PM/BQ system took 2 h to achieve a 95.7% removal. The optimal molar ratios of [P M](o): [BS](o) and [PM](o): [BQ](o) were determined to be 1:5 and 1:0.1, respectively. Interestingly, both the degradation of CBZ in the PM/BQ and PM/BS systems were dependent on dissolved oxygen (DO) concentration. When DO was around 0.5 mg L-1, the removals of CBZ by the PM/BQ and PM/BS systems were just 3.6% and 36.8%, respectively after 2 h, significantly lower than those under 9.1-mg L-1 DO (95.7% and 96.6%, respectively). Based on the quenching experiments, the enhanced degradation in the PM/BQ system was mainly ascribed to the formations of Mn(III) and O-1(2), while the formations of SO5 center dot- and SO4 center dot- mainly contributed to the accelerated degradation in the PM/BS system. The transformation products of CBZ in both the PM/BQ and PM/BS systems were identified and the degradation pathways including dehydrogenation, alkylation, carboxylation and hydroxylation were proposed. The inorganic activation of PM by BS exhibits a higher degradation rate and stability under different water matrices, indicating its potential engineering application in water treatment.