Removal of Persistent Organic Contaminants by Electrochemically Activated Sulfate

Abstract

Solutions of sulfate have often been used as background electrolytes in the electrochemical degradation of contaminants and have been generally considered inert even when high-oxidation-power anodes such as boron-doped diamond (BDD) were employed. This study examines the role of sulfate by comparing electro-oxidation rates for seven persistent organic contaminants at BDD anodes in sulfate and inert nitrate anolytes. Sulfate yielded electro-oxidation rates 10-15 times higher for all target contaminants compared to the rates of nitrate anolyte. This electrochemical activation of sulfate was also observed at concentrations as low as 1.6 mM, which is relevant for many wastewaters. Electrolysis of diatrizoate in the presence of specific radical quenchers (tert-butanol and methanol) had a similar effect on electro-oxidation rates, illustrating a possible role of the hydroxyl radical ((•)OH) in the anodic formation of sulfate radical (SO4(•-)) species. The addition of 0.55 mM persulfate increased the electro-oxidation rate of diatrizoate in nitrate from 0.94 to 9.97 h(-1), suggesting a nonradical activation of persulfate. Overall findings indicate the formation of strong sulfate-derived oxidant species at BDD anodes when polarized at high potentials. This may have positive implications in the electro-oxidation of wastewaters containing sulfate. For example, the energy required for the 10-fold removal of diatrizoate was decreased from 45.6 to 2.44 kWh m(-3) by switching from nitrate to sulfate anolyte.

Degradation of Atenolol with Electrochemical Oxidation at Mixed Metal Oxide Electrodes Assisted by UV Photolysis

“…Sulfate, chloride, and nitrate solutions are often used as supporting electrolytes in the electrochemical oxidation processes . Figure b shows the results obtained in the photo‐electrolysis process with different electrolytes.…”

Environmental Applications of Boron‐Doped Diamond Electrodes: 1. Applications in Water and Wastewater Treatment

“…Compared to nitrate anolyte, yield of sulfate anolyte is seven‐fold higher for diatrizoate and iopromide degradation, two‐fold for toc removal and six‐fold for sulfamethoxazole degradation . This process is found effective for the degradation of diatrizoate,, sulfamethoxazole, iopromide,, ciprofloxacin, nitrobenzene, carbamazepine, tribromophenol, triclopyr and triclosan …”

“…It has been demonstrated that sulfate radicals can be generated at the BDD anode surface using sulfate ions apart from conventional persulfate and peroxymonosulfate as precursors . Compared to nitrate anolyte, yield of sulfate anolyte is seven‐fold higher for diatrizoate and iopromide degradation, two‐fold for toc removal and six‐fold for sulfamethoxazole degradation .…”

Nature, Mechanisms and Reactivity of Electrogenerated Reactive Species at Thin‐Film Boron‐Doped Diamond (BDD) Electrodes During Electrochemical Wastewater Treatment

“…[128,129] As such, there is formation of reactive sulfate species as secondary oxidants that can enhance the efficiency of the process. Most electrochemical wastewater/water treatments on laboratory scale are conducted in sulfate medium owing to its conductivity, non-halogenated properties and relative abundance.…”