Degradation of Nitrobenzene Wastewater via Iron/Carbon Micro-electrolysis Enhanced by Ultrasound Coupled with Hydrogen Peroxide

The zero valent iron/granular active carbon (ZVI/GAC) micro-electrolysis enhanced by ultrasound (US) coupled with hydrogen peroxide (H2O2) was investigated for the deep degradation of nitrobenzene-containing wastewater. The results of scanning electron microscopy-energy dispersive X-rays analysis (SEM-EDS) demonstrated that continuously accelerated regeneration of ZVI and GAC in situ by US could improve the process for converting nitrobenzene (NB) to aniline (AN). H2O2 was decomposed catalytically by the byproduct Fe2+ ions generated in the micro-electrolysis process to hydroxyl radicals and the organic pollutants in the wastewater were finally mineralized to CO2 and H2O. Effects of the ZVI dosage, the ZVI/GAC mass ratio, the initial pH value and the H2O2 dosage on the efficiency for degradation of NB were studied in these experiments. The optimal operating conditions covered a ZVI dosage of 15 g/L, a ZVI/GAC mass ratio of 1:2, an initial pH value of 3 and a H2O2 dosage of 4 mL. In this case, the NB removal efficiency reached 97.72% and the total organic carbon (TOC) removal efficiency reached 73.42% at a NB concentration of 300 mg/L. The reduction of NB by USZVI/ GAC followed the pseudo-first-order kinetics model, and the pseudo-first-order rate constants were given at different initial pH values. The reaction intermediates such as AN, benzoquinonimine, p-benzoquinone, p-nitrophenol and other organic acids were detected and a probable pathway for NB degradation has been proposed.