Electrochemical denitrification of highly contaminated actual nitrate wastewater by Ti/RuO2 anode and iron cathode

[Display omitted] •Denitrification of actual industry wastewater with high nitrate concentration.•Optimization of different parameters like time, pH and current density.•Surface characteristics of electrode before and after experiments.•Kinetic study of denitrification.•Proposal of reduction mechanism on the basis of reaction intermediates identified, and operating cost analysis. The main objective of denitrification process is to obtain N2 as the final product by reduction of NO3− along with simultaneous oxidation of by-products like NH4+ and NO2−. In this study, Ti/RuO2 and Fe were used as anode and cathode, respectively, for the treatment of actual wastewater containing high concentration of nitrate ion. The current density (J = 142.86–428.57 A/m2), wastewater pH (4–12) and time (t = 15–180 min) were the main studied operating parameters for the electrochemical (EC) reduction and oxidation of real industrial wastewater containing nitrate (NO3−), ammonium ion (NH4+) and chloride. Faraday law was applied for the calculation of specific energy consumption (SEC) during the process. The maximum NO3− reduction efficiency of ≈46% was obtained at J = 214.29 A/m2 after 180 min with SEC = 149.7 kWh/kg NO3− reduced. Maximum total nitrogen (TN) removal efficiency of ≈51% was obtained at pH = 12 and J = 285.71 A/m2 with SEC = 220.7 kWh/kg NO3− reduced. The reaction mechanism and pathway was established for the EC reduction of NO3− and oxidation of NH4+ and NO2− simultaneously. Field emission scanning electron microscope (FE-SEM) coupled with energy dispersed X-ray (EDX), atomic force microscopy (AFM) and X-ray diffraction (XRD) were used for the characterization of electrodes before and after wastewater treatment. Reaction intermediates were identified by using gas chromatograph coupled with mass spectroscopy (GC/MS). Operational cost analysis for this wastewater has been done on the basis of lab scale reactor and compared with previously reported for other industrial wastewater. Interestingly no sludge and/or scum was produced during the treatment. This study provides better understanding of the reduction of NO3− as well as further oxidation of by-products.