Factors influencing critical flux in membrane filtration of activated sludge

✍ Scribed by Sayed S Madaeni; Anthony G Fane; Dianne E Wiley

• Publisher: Wiley (John Wiley & Sons)
• Year: 1999
• Tongue: English
• Weight: 150 KB
• Volume: 74
• Category: Article
• ISSN: 0268-2575
• DOI: 10.1002/(sici)1097-4660(199906)74:6<539::aid-jctb70>3.0.co;2-x

✦ Synopsis

Membrane ®ltration of biomass is usually accompanied by signi®cant ¯ux decline due to cake-layer formation and fouling. Cross¯ow ®ltration with ¯ux controlled by pumping the permeate can produce stable ¯uxes if a `critical ¯ux' is not exceeded. Below critical ¯ux the transmembrane pressure is typically very low and increases linearly with imposed ¯ux. Above the critical ¯ux the transmembrane pressure rises rapidly signifying cake-layer formation which is usually accompanied by a continued rise in transmembrane pressure and/or a drop in delivered ¯ux. A range of micro-®ltration and ultra®ltration membranes with pore sizes from 0.22 to 0.65 mm and molecular weight cutoff of 100 kDa was used. The feed was an activated sludge mixed liquor with concentration in the range of 3±10 g dm À3 . The results show that the critical ¯ux depends on feed concentration and cross¯ow velocity, being higher for higher cross¯ow velocity or lower feed concentration. Critical ¯ux was also dependent on membrane type, being lower for hydrophobic membranes. Although the transmembrane pressure was higher for the larger pore size membrane, no signi®cant difference in critical ¯ux was observed among different pore size membranes.