Electrochemical nitrate reduction by using a novel CoO/Ti cathode.

CoO film coated on Ti substrate is prepared using sol-gel method and applied as cathode material for electrochemical denitrification in this research. Preparation conditions including precursor coating times and calcination temperature are optimized based on NO-N removal, NO-N generation, NH-N generation and total nitrogen (TN) removal efficiencies. The influences of electrolysis parameters such as current density and NO-N initial concentration are also investigated. In comparison with other common researched cathodes (Ti, Cu and FeO/Ti), CoO/Ti exhibits better NO-N removal and NH-N generation efficiencies. In order to remove NO-N completely from water, Cl is added to help further oxidize NH-N to N. TN removal after 3 h treatment increases from 65% to 80%, 90% and 96% with the increase of Cl from 0 mg L to 500, 1000 and 1500 mg L, respectively. The mechanisms of NO-N reduction on cathode and NH-N oxidation on anode in the absence and presence of Cl are investigated in a double-cell reactor. Actual textile wastewater containing both NO and Cl is also treated and the CoO/Ti cathode exhibits excellent stability and reliability. It is interesting to find out that FeCl-HO Fenton pretreatment is needed to remove extra COD and provide more Cl to help oxidize NH-N to N at the same time.