Dual Oxidant System for In Situ Treatment of Organic Contaminants

Abstract

Recently, the potential catalytic properties of manganese dioxide have attracted attention as a means to activate persulfate. This focus of this research was on the potential ability of MnO2(s) solids synthesized through permanganate oxidation of organics to activate persulfate. A combined permanganate + persulfate (PM/PS) system is proposed for the treatment of organic compounds. In this system, a limited mass of permanganate is first introduced into a contaminated zone to generate MnO2(s) and then, after an appropriate reaction period, persulfate is delivered and activated by MnO2(s) for enhanced treatment. MnO2(s) generated from non-aqueous phase trichloroethylene (TCE) and potassium permanganate were employed to activate persulfate for the treatment of 1-methylnaphthalene in a series of batch experiments at various MnO2(s) to persulfate mass ratios. The results from these batch experiments showed that MnO2(s) is capable of activating persulfate. The highest 1-methylnaphthalene degradation rate was achieved at a mass ratio 20 g MnO2(s) /g persulfate with synthetic groundwater. The mass of 1-methylnaphthalene removed increased with an increase in MnO2(s) dosage. The degradation of 1-methylnaphthalene using a mass ratio 5:1 (g MnO2(s): g PS) with Milli-Q water was slightly higher than for unactivated persulfate. The degradation kinetics of 1-methylnaphthalene by persulfate activated by MnO2(s) solids was one order of magnitude higher than that achieved by unactivated persulfate. The surface of MnO2(s) solids remained unaltered during the experiment period. The performance of the PM/PS system for the degradation of aqueous phase benzene and TCE was investigated in a series of batch reactors. The PM/PS system produced higher benzene degradation than unactivated persulfate for the same mass of PS consumed. Bench-scale stop-flow column systems that closely mimic in situ conditions were executed to evaluate the performance of the proposed PM/PS system for the treatment of a residual TCE and 1-methylnaphthalene mixture. The TCE and 1-methylnaphthalene mass removed in the PM/PS system was 11% and 25% higher than by only permanganate or persulfate, respectively. Based on the findings from batch and column experiments, the minimum permanganate to persulfate molar ratio for effective treatment is 13:1. The results of this research confirm that MnO2(s) solids are able to enhance persulfate reactivity, and that the proposed PM/PS system is a promising remedy for the treatment of soil and groundwater contaminated with organic compounds. The research efforts provide key insights into the design of a PM/PS system for ISCO.