Electrochemical tests of nitrate reduction on Boron-Doped Diamond cathode are investigated through a Design of Experiments (DOE) method. The results show good reduction of nitrate into almost exclusively N2. In the studied domain, the best experimental conditions are high initial nitrate content, low acidic pH values and low working current densities. The application of DOE conclusions on an agro-industrial wastewater gives really satisfying results: final nitrate contents lower than 50 mg/L without nitrite or ammonium formation, and with low energy consumption (under 25 kWh/kgNO3).