Electrochemical Degradation of Nitrobenzene Wastewater: from Laboratory Experiments to Pilot-Scale Industrial Application

In this study, the electrochemical degradation of nitrobenzene (NB) was conducted on the Ti/SnO2-Sb/Ce-PbO2 anode with excellent functional performance. The effect of applied current density, electrode distance, pH value and initial concentration on the reaction kinetics of NB was systematically studied. The total organic carbon (TOC) removal rate reached 91.5% after 60 min of electrolysis under optimal conditions. Eight aromatic intermediate products of NB were identified by using a gas chromatography coupled with a mass spectrometer, and two aliphatic carboxylic acids were qualitatively analyzed using a high-performance liquid chromatograph. The electrochemical mineralization mechanism of NB was proposed based on the detected intermediates and the identified key active oxygen specie. It was supposed that the hydroxyl radical produced on an anode attacked NB to form hydroxylated NB derivatives, followed by the benzene ring opening reactions with the formation of aliphatic carboxylic acids, which mineralized to CO2 and H2O. In addition, NB was reduced to less stable aniline on the cathode surface, which resulted in actualized mineralization. The successful pilot-scale industrial application in combination with wastewater containing NB with the influent concentration of 80–120 mg L−1 indicated that electrochemical oxidation has great potential to abate NB in practical wastewater treatment.