BACKGROUND: In this work, the electrolysis and photo-electrolysis of dimethyl phthalate (DMP, a widely-use plasticizer) using conductive-diamond anodes are studied. RESULTS: Electrolysis and photo-electrolysis are suitable technologies for the removal of DMP from aqueous wastes. Within the range of current densities studied (20-120 mA cm(-2)), complete mineralization is achieved. UV light irradiation appears to improve mineralization and chemical oxygen demand removal rates, but not DMP removal rates, which worsened with light. The supporting electrolyte (sulfate or chloride salt) plays an important role in the electrochemical oxidation mechanisms but not in single photolysis treatment. Electrochemical mineralization is more efficient in sulfate media due to the formation of chlorates and perchlorates with diamond electrodes in chloride media. Oxidation by photolysis, electrolysis and coupled photo-electrolysis begins with attacks on the methyl ester groups, continues with the breakage of the aromatic ring, and forms carboxylic acids. The process conditions are very harsh, and only small concentrations of intermediates were found. CONCLUSIONS: Electrolysis and photo-electrolysis with conductive-diamond anodes led to the complete mineralization of DMP with an almost negligible formation of intermediates. Light irradiation significantly improved mineralization and COD removal, but not DMP degradation. Chloride anions led to less efficient electrolysis than sulfate anions. (C) 2014 Society of Chemical Industry