Enhancement of cottonseed oil refining wastewater treatment by zero valent iron under sunlight irradiation and O2 bubbling

This study is the first to apply a zero-valent iron (ZVI) system in the treatment of cottonseed oil (CTO) refining wastewater. The results indicated that the ZVI system can effectively degrade and mineralize CTO in the wastewater, whereas sunlight irradiation and O 2 bubbling can considerably enhance CTO degradation, removing 93.5% of CTO and 69.0% of chemical oxygen demand within 180 min. In addition, a low concentration (0.1 mM) of S O 4 2 - and Cl − in the wastewater improved CTO degradation, whereas a high concentration (>1 mM) of these anions considerably inhibited the degradation process. However, N O 3 - at all concentrations hindered CTO degradation. Furthermore, OH and O 2 - were the main active species for CTO degradation in the ZVI system under dark conditions. However, in addition to these two species, photogenerated hole (h + ) played a key role in CTO degradation under sunlight irradiation. This observation might be derived from the photocatalytic effect due to photoexcitation of the iron corrosion product, γ-FeOOH. Our findings show that the ZVI system assisted by sunlight irradiation and O 2 bubbling is feasible for CTO-refining wastewater treatment and can guide the real wastewater treatment project.