Mechanistic kinetic modeling of simultaneous electrochemical nitrate reduction and ammonium ion oxidation in wastewater

Two kinetic models, i.e., schemes, surface adsorbed nitrogen as divergent (SND) and surface adsorbed NO as divergent (SNOD) towards NH4+ and N-2 production, were developed to model simultaneous electrochemical reduction of the nitrate ion (NO3) and oxidation of by-products. Experimental data for electrochemical reduction was collected in synthetic nitrate solution and actual wastewater using Al and Ti/RuO2 as cathode and anode, respectively. Sum of square errors (SSE) and Akaike's information criterion (AIC) analysis showed that the SND model well-represented all the concentration profiles of nitrogen species with the variation in all the operating parameters. Desorption of nitrite ion from the cathode surface was the rate-determining step for the SND kinetic model. Mechanistic and kinetic analysis suggested that N-2 gas was the main product. However, NO2 gets formed as the by-product in the alkaline environment, whereas, NO2 and NH4+ were the by-products in the acidic environment. (C) 2021 Elsevier Ltd. All rights reserved.