Evaluation of the Performance of Different Anodes in the Electrochemical Oxidation of Ammonia

Three commercial electrodes, Ta-Ir/TiO2, Rh-Ir/TiO2, and PbO2/TiO2, were used as electrochemical anodes, and their performance was evaluated by the electrochemical oxidation of ammonia at neutral pH in a continuous electrochemical quadrangular reactor. Based on the cyclic voltammetry scans and volt-ampere relation analysis, in direct oxidation, the oxygen evolution from H2O2 decomposition was completely inhibited, and more •OH radicals could be then generated over PbO2/TiO2 and in the presence of powder activated carbon (PAC). PbO2/TiO2 can be indicated as an appropriate for the direct electrooxidation of ammonia in an unpacked bed reactor. While the efficiency for direct oxidation of ammonia was similar for the three anodes in a PAC packed reactor due to the presence of PAC could avoid short circuit and enhance electric efficiency. In indirect oxidation mediated by active free chlorine, Rh-Ir/TiO2 was the most effective in ammonia removal when chloride was present in the reaction system, and the disappeared ammonia was mainly transferred to N2, and only a small part was converted into nitrate (there was no nitrite detected during the reaction). The results indicated that Rh-Ir/TiO2 had the highest oxidation capability for ammonia compared with Ta-Ir/TiO2 and PbO2/TiO2. Hence, Rh-Ir/TiO2 based on a PAC packed bed reactor provides an alternative for the treatment of ammonia wastewater with high chloride concentration.