Chlorine mediated indirect electro-oxidation of ammonia using non-active PbO2 anode: Influencing parameters and mechanism identification

Removal of ammonia-nitrogen from wastewater has gained considerable attention in recent years to reduce the critical problems arising in the water bodies receiving ammonia containing wastewater. Eutrophication and formation of odors due to wastewater discharging, the formation of undesirable by-products during the disinfection process can be significantly reduced using various treatment technologies. Although biological processes are mainly implemented to reduce ammonia-nitrogen concentration, several studies demonstrated electro-oxidation process as a potential alternative for ammonia-nitrogen removal. Among the non-active anodes, the majorly studied anode for chlorine mediated ammonia oxidation is boron-doped diamond anode. In this study, a non-active but comparatively low-cost graphite/PbO2 anode has been proposed for removing ammonia-nitrogen from wastewater. The study describes the effects of three influencing factors; current intensity, initial Cl− and NH3-N concentration on the oxidation efficiency of ammonia using graphite/PbO2 anode. The ammonia removal efficiency was found to be dependent on all the three parameters selected. The NH3-N removal efficiency of 96.5 ± 0.4% was achieved after 120 min of electro-oxidation of 100 mg L−1 NH3-N and 900 mg L−1Cl− containing solution at a current intensity of 0.3 A. Nitrate ion, and nitrogen gas were found as the stable end-products of the ammonia removal process. The formation of desirable end-product, N2, increased from 11.6% to 28.9% with increase in Cl− concentration from 300 to 1500 mg L−1. The steady-state concentrations of chloramine indicate formation of chloramine as an intermediate step of ammonia-nitrogen removal. The total chloramine concentration was <2.5% of the initial nitrogen content throughout the reaction.