PVDF membranes modified with diblock copolymer PEO-b-PMMA as additive: Effects of copolymer and barrier pore size on filtration performance and fouling in a membrane bioreactor

In the present work, filtration performance and fouling behavior of four poly(vinylidene difluoride) (PVDF) membranes with different composition and molecular weight cut-off (MWCO) were investigated in a lab-scale submerged membrane bioreactor (MBR) system, treating real pharmaceutical wastewater. Poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-b-PMMA) diblock copolymer or FeCl2 or the combination of PEO-b-PMMA and FeCl2 were used as special additives during membrane formation. A 30-day filtration experiment was performed using four membranes in the same aeration tank simultaneously, and filtration performance of the membranes was investigated over the entire filtration period. Fouling parameters were calculated for all membranes and the TMP-step method was used to determine the critical flux of the membranes. Formed cake layers onto the surface of the membranes at the end of each filtration run were collected and extracellular polymeric substances (EPSs), excitation and emission matrix (EEM) fluorescence spectroscopy, and Fourier transform infrared (FTIR) spectroscopy analyses were performed for the cake layers. Collected cake layers after EPSs extraction were dried and their masses were measured to estimate anti-biofilm formation potential of the membranes. Obtained results revealed that incorporation of the PEO-b-PMMA diblock copolymer into the PVDF membrane accompany with FeCl2 salt which tailors the MWCO and prevents the increment of the pore size improves membrane performance and reduces its fouling propensity, in a way that membrane with smaller MWCO containing copolymer revealed lower flux decline, higher critical flux, higher flux recovery ratio (FRR) and lower biofilm mass per area. Moreover, EPS and EEM analyses revealed that membrane surface chemistry has considerable effect on the composition of the cake layers. Finally, chemical oxygen demand (COD) removal efficiency proved that MWCO does not have obvious effect on effluents' quality. The present study confirms the importance of the surface chemistry and MWCO on fouling behavior of the membranes in the MBR system and reveals that the addition of the PEO-b-PMMA diblock copolymer to the PVDF membrane improves anti- fouling property of the membrane considerably. (C) 2022 Published by Elsevier Ltd on behalf of Institution of Chemical Engineers.