Towards Use of Persulfate Electrogenerated at Boron Doped Diamond Electrodes as Ex-Situ Oxidation Approach: Storage and Service-Life Solution Parameters

Abstract

To date, a wide range of synthetic and real effluents have been treated using in situ electrochemically driven BDD-SO4 2−/SO4 ·−/S2O8 2− systems to eliminate persistent organic pollutants and microorganisms. Although reactive sulfate-based species are electrochemically generated in situ with free heterogenous ·OH radicals, SO4 2−/SO4 ·−/S2O8 2− species have a half-life greater than that of the ·OH radicals. However, no information has been published regarding the properties of the oxidant solution after its electrochemical synthesis. Here, an electrochemical BDD-SO4 2−/SO4 ·−/S2O8 2− system was evaluated in terms of solution oxidation power as a function of storage temperature, storage time, and ex situ applicability. Results clearly show that storage temperature has an influence on the storage and service-life of the solutions called fresh-persulfate (25 °C) or cold-persulfate (10 °C). Greater stability in the cold-persulfate solution was observed, as a function of time, and it was effective in degrading organic pollutants as an ex situ oxidation approach, eliminating 80.73%, 79.25%, and 63.25% after 120 min for methyl orange dye, 1,4-benzoquinone (1,4-BQ), and caffeine, respectively. Cold-persulfate solution also proved to be a feasible off-grid technology after 14 days storage. These results contribute to understanding of the fundamentals of sulfate aqueous solutions as precursors of sulfate-based oxidizing solutions and their applications.