Potential use of green TiO2 and recycled membrane in a photocatalytic membrane reactor for oil refinery wastewater polishing

Abstract

Membrane bioreactors (MBRs) have been successfully used in oil refinery wastewater treatments. However, a polishing treatment of the MBR permeate is required to remove the recalcitrant organic compounds. In this study, the coupling of a photocatalytic membrane reactor (PMR) and MBR was investigated for the treatment of oil refinery wastewater. Titanium dioxide (TiO2) nanoparticles, synthesised by a cleaner route assisted by microwave radiation, and recycled membrane, an end-of-life reverse osmosis membrane converted to an ultrafiltration membrane by oxidation, were prepared for use as a PMR. The recycled membrane could completely retain the catalyst particles. The PMR exhibited higher efficiency and stability in the removal of organic matter than those of the individual photocatalysis and membrane processes. Adsorption of organic compounds was observed on the catalyst surface. These compounds were degraded releasing active sites for reaction/adsorption. A chemical oxygen demand analysis revealed that up to 60% of the organic matter in the MBR permeate was decomposed in the PMR, which also contributed to membrane fouling mitigation. The membrane fouling resistance in the PMR was 7.3 times lower than that in the system operated without the catalyst. In addition, membrane degradation was not observed upon the use of the catalyst. The results indicate that the PMR with the green TiO2 and recycled membrane is a highly active, stable, and promising system for the polishing of oil refinery wastewater previously treated by the MBR.