Flux enhancement for polypropylene microporous membrane in a SMBR by the immobilization of poly(N-vinyl-2-pyrrolidone) on the membrane surface

To improve its limiting flux and antifouling characteristics in a submerged membrane-bioreactor (SMBR) for wastewater treatment, polypropylene hollow fiber microporous membrane (PPHFMM) was surface-modified by the immobilization of poly(N-vinyl-2-pyrrolidone) (PVP) through air plasma treatment. Attenuated total reflection-Fourier transform infrared spectroscopy (ATR/FT-IR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) were used to characterize the structural and morphological changes on the membrane surface. Water contact angles were also measured by the sessile drop method. Results of ATR/FT-IR and XPS clearly indicated that PVP was successfully immobilized on the membrane surface. Water contact angle on the PVP-immobilized membrane showed a minimum value of 72.3°, approximately 57° lower than that on the unmodified one. The SMBR was operated at a fixed transmembrane pressure to determine the limiting fluxes of PPHFMMs with or without PVP immobilization. The maximum relative limiting flux appeared to be 159 L m−2 h−1 for the PVP-immobilized PPHFMM with an immobilization degree of 6.8 wt.%, 54.4% higher than that of the nascent PPHFMM. After continuous operation for about 50 h, flux recovery, reduction of flux, and relative flux ratio were 53% higher, 17.9% lower and 79% higher than those of the nascent PPHFMM respectively. It was found also that the Pearson correlation between total surface free energy and flux recovery was significant, which indicated that the PVP-immobilized membrane with higher total surface free energy would have excellent antifouling characteristics.