Efficient nitrate removal from water using selected cathodes and Ti/PbO₂ anode: Experimental study and mechanism verification

Selected cathodes, including carbon paper (C) and plates of titanium (Ti), iron (Fe), copper (Cu) and aluminum (Al), combined with a Ti/PbO₂ anode (a lead dioxide electrodeposited on titanium plate) were employed for studying quick nitrate removal from neutral water in this work. Cathode materials, current densities and the presence of chloride ions (Cl⁻) in water were investigated as to the effects on nitrate removal. Nitrate and two main reduction products, i.e. nitrite and ammonia, were measured using ion chromatography. The results showed that the nitrate removal efficiency decreased in the order of cathode materials: C > Ti ≈ Fe > Cu > Al. The optimum removal was achieved to be 47.7% for a 50 mg-N/L nitrate solution by using carbon paper cathode and Ti/PbO₂ anode after 120-min electrolysis with a current density of 40 mA/cm². The subsequent experimental results showed that the current density of 20 mA/cm² is also high enough for achieving a considerable nitrate removal. Moreover, the presence of Cl⁻ in water was proven to have no significant effect on nitrate removal but be able to promote the destruction of nitrite and ammonia ions, resulting in the virtual decrease in nitrate and total nitrogen. By a designed experiment, the nitrate removal pathway was confirmed to include a reciprocating reduction (of nitrate) and oxidation (of nitrite and ammonia), both of which can lead to the removal of nitrate as well as total nitrogen from nitrate-containing wastewater by generation of nitrogen. cathodes and anodes may play different roles.