Influence of operating conditions on electrochemical reduction of nitrate in groundwater

The influences of current density, initial pH, cation and anion concentrations, and the coexistence of Ca2+ and HCO3- on the efficiency of electrochemical nitrate reduction by a copper cathode and Ti/IrO2 anode in an undivided cell were studied. In the presence of 5 mM of sodium chloride (NaCl), the nitrate-nitrogen concentration decreased from 3.57 to 0.69 mM in 120 minutes, and no ammonia or nitrite byproducts were detected. The nitrate reduction rate increased as the current density increased. The electrochemical method performed well at an initial pH range of 3.0 to 11.0. The rate of nitrate reduction increased as concentrations of Na+, K+, and Ca2+ increased. The anion of the supporting electrolyte decreased the rate of reduction in the order Cl- > HCO3(2-) = CO3(2-) > SO4(2-) at both 5 mM and 10 mM of anion. The coexistence of Ca2+ and HCO3- ions could inhibit nitrate reduction. The concentration of nitrate-nitrogen in polluted groundwater decreased from 2.80 to 0.31 mM after electrolysis for 120 minutes.