Coupling photo and sono technologies to improve efficiencies in conductive diamond electrochemical oxidation

• Simultaneous UV-light and US irradiation improves the mineralization of the solution.
• There is an antagonic effect of the combination of UV-light and US on the CDEO.
• Single irradiation of light or sounds is able to improve the removal of DMP.
• There are formation of radicals in the reaction media by UV-light or US.

In this work, the improvements obtained in the conductive-diamond electrochemical oxidation (CDEO) by simultaneous coupling of ultrasounds (US) and UV-light irradiation are studied for the treatment of synthetic wastes containing dimethyl phthalate (DMP). Results show that both irradiation technologies improve significantly the rates of oxidation and mineralization of the electrolytic process, but their coupled effect on results is smaller to the effect observed when they operate separately. Results are explained in terms of the formation of radicals in the reaction media by UV-light or US decomposition of powerful oxidants formed electrochemically on the conductive-diamond surface. Oxidation of DMP proceeds through the removal of the methyl esters group, ring breakage and carboxylic acid mineralization. Concentration of intermediates is very small in electrolytes with sulfates. When chlorides are present in the electrolyte, chlorophenols are also observed and concentration of intermediates becomes greater. In terms of energy consumed, sonolysis processes are more expensive than photolysis processes to attain similar removal percentages.

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