Selective reduction of highly concentrated nitrate by electrochemical method using a combination of Zn and Ti/Ir-Ru electrodes

Treatment of wastewater contaminated by highly concentrated nitrate was studied by electrochemical method using a combination of Zn cathode and Ti/Ir-Ru anode in an undivided cell. We observed that almost 76% of initial nitrate (1,000 NO3--N mg/L) was removed in 8 h by electrodenitrification without significant production of undesirable by-products (i.e., nitrite and ammonia). Variations of pH and temperature were also monitored during the electrochemical nitrate reduction, which showed an increase in both pH (up to 12.5) and temperature (up to 41.5 degrees C), resulting in the enhanced nitrate reduction in this study. The nitrate removal efficiency increased (30% -> 76% -> 84%) as the current density increased (20 -> 40 -> 60 mA/cm(2)), but it was not a linear increase due to the increase of hydrogen evolution at high current density. The increase in paired electrode number from one to four led to the enhanced nitrate removal from 72% to 100% in 8 h reaction time. Moreover, we observed a remarkable increase in nitrate removal by using a combination of one anode and two cathodes (86% in 8 h) without productions of nitrite and ammonia due to the acceleration of nitrate reduction by increasing number of cathode.