Mineralization of citric acid wastewater by photo-electrochemical chlorine oxidation

This work demonstrates a novel chloride photo-electrochemical method for mineralizing citric acid. The electrolytic reactor with a length of 12 cm, a width of 12 cm and a height of 30 cm held 2.5 L of solution, which was involved in the batch reaction. Both anode and cathode were made of titanium coated with RuO2/IrO2. The results revealed that the solution pH dominated the production of hypochlorous acid (HOCl) oxidant in the presence of NaCl as direct current electricity was used. The chloride electrochemical process at pH 5.5 removed 59% of total organic carbon (TOC) in 4 h (NaCl = 200 mM, current = 5 A). UV irradiation (254 nm) in the reactor induced the photo-electrochemical reaction, increasing the TOC removal from 59% to 99.4%. Finally, the reaction pathway for citric acid mineralization was discussed with reference to the detection of intermediates using a liquid chromatography-mass spectrometry (LC-MS). (C) 2013 Elsevier Ltd. All rights reserved.