Unveiling the Key Roles of Various Reactive Species for Ammonia Oxidation in an Efficient Three-Dimensional Electrocatalytic System and Enlarged Scale Study for the Treatment of Practical Wastewater

Indirect electrocatalytic (EC) oxidation of ammonia into harmless N2 based on in situ generated reactive chlorine species from chlorinated aqueous streams has been considered as an effective technique for ammonia abatement from water/wastewater. However, the precise oxidation mechanism and contribution of reactive species to the ammonia oxidation are still under debate and deserved to be specifically investigated. In order to enhance mass transfer efficiency, this work systematically investigated and optimized a three-dimensional EC (3D-EC) system, which exhibits about two times higher ammonia oxidation rate compared to a two-dimensional EC system. The polarization characters of particle electrodes have been analyzed to correlate with the enhanced generation of ·OH and ClO· radicals under biased conditions, and the role of each oxidative species was specifically quantified. In the enlarged scale study, water flow-by mode was tested with varying experimental parameters including flow rate, hydraulic residence time, and secondary oxidation. Furthermore, the performance of the 3D-EC system for the treatment of six types of practical wastewater with different levels of ammonia and organics was evaluated. This study provides mechanistic insight on the indirect 3D-EC oxidation of ammonia and its potential application on ammonia wastewater treatment.