Degradation of emerging contaminants by sono-Fenton process with in situ generated H2O2 and the improvement by P25-mediated visible light irradiation

Developing advanced treatment methods to minimize the release of emerging contaminants to natural water has become a matter of considerable interest. Sono-Fenton process was investigated to degrade bisphenol A (BPA) and sulfadiazine (SDZ). The H2O2 generated in situ was used as the exclusive source. Results showed that, the 400 kHz ultrasound is more efficient in creating homogeneous sono-Fenton than the 20 kHz apparatus due to the higher production of 'OH. Influence of Fe2+ was more remarkable on the degradation of hydrophilic SDZ, and its degradation kinetics was well fitted by two-stage kinetic model. However, the Fe2+ and H2O2 were unproductively wasted, which could not be improved by changing the dosing modes of Fe2+. The presence of P25 under visible light irradiation could significantly accelerate SDZ degradation at small amount of iron precursors, mainly via promoting the Fe2+/Fe3+ cycling by the photoelectrons. Moreover, SDZ degradation in sono-Fenton process was significantly inhibited at pH > 7, but the inhibition was very weak in P25-assisted sono-Fenton process. The presence of P25 also improved the mineralization. Three primary degradation pathways of SDZ degradation were proposed, including the attacking of the benzene ring, the oxidation of the amino group and the extrusion of SO2.