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[en] Highlights: • Cathodic reduction becomes a feasible alternative to activate persulfate. • A synergistic effect of electro-PS with heat activation improve the DB3 mineralization. • Complete decolorization within 30 min was achieved at 70 °C in the synergic process. - Abstract: This work assesses the role of the operational conditions upon the electro-activation of persulfate (electro-PS) using Ti/IrO2Ta2O5 electrode for the decolorization of anthraquinone azo dye Disperse Blue 3 (DB3). The studied variables include current density (j) (5–80 mA cm−2), persulfate concentration based on the stoichiometric dose for complete DB3 mineralization (20–100%), temperature (30–90 °C) and pH (3–12) as well as the influence of dissolved oxygen. The persulfate activation from cathodic reduction was confirmed by linear sweep voltammetry (LSV). The increase in j enhanced the PS decomposition and, consequently, decolorization efficiency, because of the greater production of sulfate radicals (SO4• −). Besides, the combination of electro-PS with thermal activation resulted in a synergistic effect upon the DB3 mineralization. In the range 30–70 °C, electro-PS led to a significantly higher TOC conversion (above 60% at 40 mA cm−2) than sole heat-activated PS. This difference steeply decreased as temperature increases, achieving similar TOC conversion at 90 °C after 60 min.
[en] This work addresses the effect that plants (Typha latifolia and Carex lurida) have on the reduction of Cr(VI) in wetland sediments. Experiments were carried out using tubular microcosms, where chemical species were monitored along the longitudinal flow axis. Cr(VI) removal was enhanced by the presence of plants. This is explained by a decrease in the redox potential promoted by organic root exudates released by plants. Under these conditions sulfate reduction is enhanced, increasing the concentration of sulfide species in the sediment pore water, which reduce Cr(VI). Evapotranspiration induced by plants also contributed to enhance the reduction of Cr(VI) by concentrating all chemical species in the sediment pore water. Both exudates release and evapotranspiration have a diurnal component that affects Cr(VI) reduction. Concentration profiles were fitted to a kinetic model linking sulfide and Cr(VI) concentrations corrected for evapotranspiration. This expression captures both the longitudinal as well as the diurnal Cr(VI) concentration profiles. - The presence of plants enhances the reduction of Cr(VI) in wetland sediments by modifying the governing biogeochemical cycle