RESUMO
Polyvinylidene fluoride (PVDF) hollow fiber ultrafiltration membranes were modified with carbon nanotubes (CNT). Hybrid pre-ozonation and CNT modification were investigated by experimentally manipulating the ozonation process, threshold flux, and membrane fouling. The results showed that the threshold fluxes of the unmodified membrane and hybrid process were 45 L·(m2·h)-1 and 81 L·(m2·h)-1, respectively. Additionally, the fouling rate of the hybrid process was about 0.00137 kPa·min-1·L-1·m2·h, which was notably lower compared to other process. The results showed that the filtration volume under threshold flux was higher than that under critical flux with the same CNT loading mass and ozone dosage. This comparison indicated that membrane fouling was alleviated under threshold flux and that the corresponding operation period was extended. Through the carbon balance experiment, the fouling capacity and recoverability improved remarkably after CNT modification. Additionally, ozonation could enhance the recoverability of membranes. The hybrid process examined in this study could dramatically improve the permeability and extend the operation time of the ultrafiltration membrane.
RESUMO
Polyvinylidene fluoride (PVDF) hollow fiber ultrafiltration membranes were modified with carbon nanotube (CNT). Combined with the ozonation process, the effect of the hybrid pre-ozonation and CNT modification on fouling alleviation was investigated. The impacts of CNT loading mass and ozone dosage on the variation of flux and antifouling ability of the membrane modules were evaluated. Under a critical flux of 144 L·(m2·h)-1, CNT loading mass of 3 g·m-2, and ozone dosage(O3/DOC) of 0.22 mg·mg-1, the results revealed that the filtration volume of the hybrid process was promoted to 850 L·m-2, which was about 4.5 times higher than that of the original unmodified membrane. With a flux of 18 L·(m2·h)-1 and 15 day operation, the filtration volume was promoted to 3000 L·m-2, which was 10 times that of the unmodified membrane. The fouling membrane surface was observed using confocal laser scanning electron microscopy (CLSM). The results demonstrated that more living bacteria were present on the membrane surface of the unmodified membrane, which showed a rapid transmembrane pressure (TMP) increase. Both pre-ozonation and CNT modification decreased the total amount of microorganisms and the amount of the living bacteria as well, which mitigated the increase in TMP. After pre-ozonation, the presence of a CNT layer on the membrane surface further decreased the number of living bacteria. Although the CNT layer captured some dead bacteria, it had no obvious relationship with the increase in TMP.