TiO2 Nanoparticles Effect on PVDF Membrane Filterability in Membrane Bioreactors: Fouling Reduction and Critical Flux Enhancement

One of the important operational factors affecting the fouling of membrane bioreactors (MBR) is the critical flux which is defined as the flux above which the cake layer formation on the membrane surface is seen. So, to prevent severe fouling in MBR, it is important to determine the critical flux and operate at a flux below it. The evaluation of critical flux and pollutant removal in a lab-scale submerged membrane bioreactor was performed for a real oil refinery wastewater. Transmembrane pressure (TMP) and flux behavior in a period of time via a so-called flux step method were studied to determine the critical flux of the membrane and to investigate of the effect of TiO2 nanoparticles (NPs) incorporation into Polyvinylidene fluoride (PVDF) matrix, on the membrane filterability. The effectiveness of MBR for treating effluent stream of Dissolved Air Floatation (DAF) unit of Tehran oil refinery wastewater plant has been studied and the results showed that TiO2 NPs improved the phenol removal efficiency in such wastewater. About 70% enhancement in critical flux of PVDF/TiO2 membrane was observed as a result of TiO2 NPs tendency to reduce fouling of PVDF membranes. It was concluded that the effect of TiO2 incorporation in the membrane matrix is more significant in fouling reduction than permeability improvement and that the surface charge of the membrane plays much more important role than other surface modification strategies such as hydrophilicity enhancement, in fouling mitigation of MBRs. The results also demonstrated that TiO2 has no significant effect on the microorganism destruction or growth, since the amount of total soluble microbial products (SMP) and extracellular polymeric substance (EPS) remained almost stable during MBR operation for both membranes.