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

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.