The use of Ebonex electrodes for the electrochemical removal of nitrate ion from water

This work addresses the remediation of nitrate-contaminated water using electrodes made of Ebonex (a titanium oxide ceramic with a wide range of potential stability). The objective was the complete denitrification of solutions containing nitrate ion. Denitrification was achieved in about 50% yield with unreactive supporting electrolytes when Ebonex was used as both cathode and anode, the remaining product being ammonia. Ammonia could be re-oxidized at the Ebonex anode, but this was much less efficient than the reduction step. A more efficient electrolytic denitrification was possible for solutions containing chloride; this is oxidized anodically to hypochlorite, which then oxidizes ammonia chemically to N-2. The overall rate of denitrification was highest at moderate concentrations of chloride ion, because hypochlorite also re-oxidizes reduction intermediates such as nitrite back to nitrate. Complete denitrification was achieved at all stages of the reaction using Ebonex cathode and a dimensionally stable anode based on Ti/IrO2 or Ti/RuO2, because the DSA oxidizes chloride ion more efficiently than Ebonex. Cathode fouling by water sources that are high in hardness cations can be prevented by using one DSA and a pair of Ebonex electrodes that undergo periodic polarity reversal.