Professor, State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, China

Speech Title: Sustainable activation of persulfate by magnetite nanoparticles for degradation of refractory organic compounds

Abstract: Zero valent iron (ZVI) in form of iron filings have been tested for activation of persulfate to degrade 1,4-dioxane and the activation was not sustainable due to side reactions to significantly consume persulfate and ZVI. Granular magnetite solids has shown good ability to activate persulfate to degrade chlorinated solvent compounds and 1,4-dioxane. This was demonstrated by the observations that degradation of a variety of contaminants was all preferential to production of soluble iron and minimal soluble iron was released before depletion of the contaminants. The surface chemical structures of the magnetite solids did not change after degradation of the contaminants were completed. These results also indicated that the magnetite behaved like catalyst for persulfate activation. However, the rate of degradation reaction is not high enough, and use of nano-size of magnetite may enhance the rate due to significantly larger surface area of the nanoparticles. In this study, magnetite nanoparticles (MNPs) emplaced in silica sands were examined to in situ activate persulfate to degrade 1,2-DCA using 1-D column reactive transport experiments. Long-term experiments were implemented to test the sustainability of the magnetite nanoparticles to degrade the contaminants, and to examine the catalytic behaviour for activation. The MNPs were emplaced into the column through a facilitated transport method using carbxymethyl cellulose as the facilitative reagent. Four columns were prepared for the reactive transport experiments, which were a clean sand column, a sand column containing 1.9% of MNPs, a sand column containing 5.4% of MNPs, and a sand column containing 9.4% of MNPs. Solutions of DCA, or a mixture of persulfate and DCA with a molar ratio of 2:1, 5:1 or 20:1, were injected into the columns. The results showed that the MNPs in the sand porous media can successfully activate persulfate to degrade DCA under dynamic flow conditions and DCA removal efficiency increased with the increasing persulfate concentration, with a fully liberation of chloride caused by persulfate at the molar ratio of 20:1 between persulfate and DCA. Increasing MNPs content in the column did not have significant effect on DCA removal efficiency. In the long-term experiments, the degradation efficiency of pollutants was still up to 21%, after injection of 880 PVs of mixture of persulfate and DCA with a molar ratio of 20:1. The total iron in effluent was less than 0.61 mg/L in the process. The results showed that MNPs is sustainable to active persulfate for the degradation of DCA. These findings show great potential of MNPs in enhancing persulfate-based in situ chemical oxidation for remediation of chlorinated solvent contaminated sites.