Persulfate/Peroxide Oxidation Activated by Ferrous Ions Using Methylene Blue: Development of a Screening Technique for the Production of Radicals.

Oxidation by metal activated persulfate and peroxide produces sulfate radicals ( SO 4 • − ) and hydroxyl radicals ( ∙ O H), powerful oxidants that can be used for the destruction of a wide range of pollutants in water and wastewater. In this study, methylene blue dye was used as an indicator to determine the reaction kinetics and identify the radicals produced during oxidation by persulfate, which was added in the form of monopersulfate, and peroxide in the presence of ferrous ions. There was a positive correlation between the monopersulfate concentration and the degradation of methylene blue in the absence of ferrous ions at pH 3, 5, and 7. In the absence of ferrous ions, peroxide had little to no effect on the degradation of methylene blue. Fe2+/monopersulfate and Fe2+/peroxide systems at a ratio of 0.5:1 resulted in the rapid degradation (<20 min) of methylene blue. Humic acid, at a concentration as high as 20 mg/L, did not affect the degradation kinetics in both systems. Bicarbonate inhibited the Fe2+/peroxide reaction; however, in the Fe2+/monopersulfate system, the scavenging effect of bicarbonate was inhibited at higher concentrations, that is, <100mM. The dominant radical species in Fe2+/monopersulfate system was identified as the SO 4 • − using ethanol and tert-butyl alcohol as probes. This screening method was validated by using the same oxidation conditions for the degradation of microcystin-LR (MC-LR). Similar reaction kinetics were observed between MC-LR and monopersulfate. Fe2+/monopersulfate and Fe2+/peroxide reactions resulted in the rapid degradation of MC-LR. Humic acid and bicarbonate had a similar effect on the MC-LR degradation. SO 4 • − was again identified as the dominant radical species in degradation of MC-LR in the Fe2+/monopersulfate system. [ABSTRACT FROM AUTHOR]