Kinetic study of the simultaneous electrochemical removal of aqueous nitrogen compounds using BDD electrodes

This work investigates the kinetic behavior of aqueous nitrogen compounds in an electrochemical cell provided with boron doped diamond (BDD) anode and cathode electrodes. Starting with initial solutions of sodium nitrate or sodium nitrite and using NaCl as electrolyte in a concentration range from 0 to 28.2 mol/m(3) the experiments were carried out working at constant current density of 400 A/m(2) and the change in the concentration of nitrite, nitrate, ammonia, chloramines and chlorinated ions was experimentally analyzed. In the absence of chloride in the bulk solution oxidation reactions took place much faster than reduction reactions and the oxidation rate was further increased in the presence of chloride. Chloride exerted the strongest influence on the oxidation rate of nitrite and ammonia. With respect to the influence of chloride on the reduction rate of nitrate at first it appeared an apparent negative influence that afterwards was explained through the coupled influence of the presence of nitrite ions in the aqueous medium that were oxidized to nitrate almost instantaneously thus increasing the concentration of the former ions. Previous works have reported either a positive or a negative influence of chloride on the reduction of nitrate: we advance the former explanation by pointing out the coupled influence of the dissolved nitrogen compounds on the individual removal kinetics. Finally a kinetic analysis of the reaction pathway has been proposed and the rates of the elementary reactions have been fitted to pseudo-first order equations obtaining the values of the kinetic constants. (C) 2012 Elsevier B.V. All rights reserved.