Activation of persulfate for tetracycline degradation using the catalyst regenerated from Fenton sludge containing heavy metal: Synergistic effect of Cu for catalysis

Abstract

Fenton reaction has been widely applied as a unique oxidative method in the treatment of industrial wastewater. However, it generates a massive amount of Fe sludge, which mostly contains other hazardous heavy metal waste that can harm the environment and humans. In this study, we proposed a sustainable method to eliminate the side effect of the Fenton reaction and turn the Fenton sludge containing Cu into an efficient catalyst in the activation of peroxymonosulfate (PMS) to degrade tetracycline (TC). The existence of Cu, which can increase the oxygen vacancies of the sludge, is attributed to the activation efficiency compared with Fe sludge devoid of Cu. X-ray diffraction and X-ray photoelectron spectroscopy results show that Fe is present in the form of α- Fe2O3 and γ- Fe2O3, whereas Cu mostly exists in the valence state of Cu(II). The influence of catalyst and PMS dosage, pH, and recycling times on the PMS reaction is illustrated. OH, SO4− O2– and 1O2 are the critical reactive oxygen species. TC can be decomposed into CO2 and H2O through six possible pathway processes with these free radicals. Given its sustainable treatment and high catalytic efficiency, dealing with Fe sludge that contains heavy metals serves as a modal practice for harmful waste treatment and can be popularized for a broader application.