Electrochemical nitrate reduction by using a novel Co3O4/Ti cathode.

Co3O4 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 NO3--N removal, NO2--N generation, NH4+-N generation and total nitrogen (TN) removal efficiencies. The influences of electrolysis parameters such as current density and NO3--N initial concentration are also investigated. In comparison with other common researched cathodes (Ti, Cu and Fe2O3/Ti), Co3O4/Ti exhibits better NO3--N removal and NH4+-N generation efficiencies. In order to remove NO3--N completely from water, Cl- is added to help further oxidize NH4+-N to N2. TN removal after 3 h treatment increases from 65% to 80%, 90% and 96% with the increase of Cl- from 0 mg L-1 to 500, 1000 and 1500 mg L-1, respectively. The mechanisms of NO3--N reduction on cathode and NH4+-N oxidation on anode in the absence and presence of Cl- are investigated in a double-cell reactor. Actual textile wastewater containing both NO3- and Cl- is also treated and the Co3O4/Ti cathode exhibits excellent stability and reliability. It is interesting to find out that FeCl2-H2O2 Fenton pretreatment is needed to remove extra COD and provide more Cl- to help oxidize NH4+-N to N2 at the same time.