The research of steady-state electrochemical kinetics of effective and selective conversion of total nitrogen to N2

The electrochemical conversion of inorganic nitrogen forms (i.e., NO3−-N, NO2−-N, and NH4+-N) to N2 was studied using Ti as cathode and Ti/PbO2 as anode in the simulated wastewater. According to linear sweep voltammetry, nitric nitrogen was effectively converted to N2 on Ti cathode at the working potential more negative than − 1.1 V (vs. SCE). Ti/PbO2 anode had the working potential of + 0.8 V (vs. SCE) for NH4+-N converted to N2. The apparent rate constants of NO3−-N to NO2−-N and NO2−-N to N2 were 2.46 × 10−2 min−1 and 4.03 × 10−2 min−1, respectively. The kinetic analyses revealed that the reduction of NO3−-N was a two-step process, and NO2−-N was an unstable intermediate, which could be easily oxidized to NO3−-N or reduced to NH4+-N. The majority of NH4+-N could be effectively converted to N2 on Ti/PbO2 anode with the apparent rate constants of 5.12 × 10−2 min−1. The dual-chamber (DC) reactor with circulation was used in the batch electrolysis of simulated and actual wastewater. The results verified the pathways of NH4+-N oxidation and NO3−-N reduction and achieved high conversion rate of total nitrogen (TN) to N2.