Mineralization of organic acids by the photo-electrochemical process in the presence of chloride ions

• We designed a photoelectro-active chlorine process for treatment of organic acids.
• Effects of pH and UV irradiation on chlorine dominant were elucidated.
• Above 90% of TOC was removed for all selected organic acids.

This investigation demonstrates an indirect chloride photo-electrochemical method for mineralizing the organic acids (5 mM), including acetic, maleic, malonic, citric, oxalic, and succinic acids. The electrolytic reactor (12 cm × 12 cm × 30 cm) held 2.5 L solution, in which both anode and cathode were the titanium-based dimensionally stable anode (Ti-DSA) that was coated with RuO2/IrO2. Different active chlorine species with various redox potentials, including OCl−, HOCl, and Cl2, produced in NaCl medium were the major oxidants depending on the pH of the electrolysis. The results revealed that a pH in the range 2.5–7 maximized the removal rate of total organic carbon (TOC) of citric acid solution. The UV-254 nm light was then utilized in the NaCl electrolysis to support a photo-electrochemical reaction. The substantial improvement in the mineralization efficiency for all organic acids was attributed to the hydroxyl radicals (OH) and chlorine radicals (Cl) from HOCl upon activation by the UV irradiation.