Microfiltration of Activated Sludge Using Modified PVC Membranes: Effect of Pulsing on Flux Recovery

Abstract

A combined effect of backpulsing, crosspulsing, and membrane-surface modification was investigated for the reduction of membrane fouling and the recovery of flux for crossflow filtration. The hydrophobic poly(vinyl chloride) (PVC) membranes were subjected to the surface modification with N-vinyl-2-pyrrolidinone (NVP) monomer by the ultraviolet-assisted graft polymerization to increase the surface wettability and to decrease the adsorptive fouling. The flux was dependent on the membrane-surface properties. The flux of the modified membrane was higher than that of the unmodified membrane due to the increase of hydrophilicity on the membrane surface and the more or less dilution of protein concentration in the sludge solution at NVP layer. The recovered fluxes of modified and unmodified membranes, after the removal of the foulants from the membrane surface, were about 61% and 34% of the initial flux, respectively. These results suggest that the adhesive interactions of the mixed liquor-suspended solid (MLSS) with the hydrophilic membrane surfaces are weaker than those with a hydrophobic surface. To clean foulants, backpulsing and crosspulsing were carried out. 3.6-fold and 5.6-fold enhancements of modified membranes in the average permeate flux, in comparison with unmodified membranes, were obtained for filtering MLSS using backpulsing alone and a combination of backpulsing and surface modification, respectively. The average permeate flux of surface modified membrane with backpulsing (5.6-fold) was higher than with crosspulsing (2.8-fold), indicating that the deposition of MLSS in the interior of the membrane pore was the dominant fouling mechanism. The transmembrane pressure (TMP) of modified membranes was lower than that of unmodified membrane.

Keywords:

• Microporous membrane
• Poly(vinylchloride)
• N-vinyl-2-pyrrolidinone (NVP)
• Sludge
• Crossflow filtration
• Backpulsing

Acknowledgments

Dae Sik Kim and Jong Seok Kang are grateful to the Brain Korea 21 Program sponsored by the Korea Ministry of Education for a scholarship. This work is supported by the Korea Ministry of Science and Technology under the National Research Laboratory Program in the year 2001.