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Ultrafiltration fouling control

Ultrafiltration fouling control. Demineralized water backwashing. Sheng Li Sanitary Engineering, Delft University of Technology The Netherlands. Content. Introduction Hypotheses Results Conclusion. Demi water is better than UF permeate for backwashing.

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Ultrafiltration fouling control

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  1. Ultrafiltration fouling control Demineralized water backwashing Sheng Li Sanitary Engineering, Delft University of Technology The Netherlands

  2. Content • Introduction • Hypotheses • Results • Conclusion

  3. Demi water is better than UF permeate for backwashing Why is demineralized water better? No pre-treatment! No in-line coagulation!

  4. Difference between UF permeate and demineralized water for backwashing • Divalent ions • Monovalent ions • Organic matter

  5. Hypotheses of NOM fouling • Ca-bridging effect and/or Ca complexation • Charge screening effect (DLVO theory) • NOM molecule adsorption

  6. Ca-bridging effect(filtration)

  7. Ca-bridging effect(Backwash with permeate) Ca Ca Ca Ca Ca

  8. Ca-bridging effect(Backwash with demi water)

  9. Charge screening effect(filtration)

  10. Charge screening effect(Backwash with permeate)

  11. Charge screening effect(Backwash with demi water)

  12. Results(Impact of calcium, flux: 85 lmh) No pre-treatment! No in-line coagulation!

  13. Results(Impact of sodium, flux: 85 lmh) No pre-treatment! No in-line coagulation!

  14. Experiment set-up and Material • UF set-up: “MFI-UF” (Kiwa Water Research, NL) • Membrane: Capillary membrane, 0.8 UFC M5 (X-Flow), with a surface area of 0.07 m2

  15. Backwash solutions • Demineralized water • UF permeate • UF permeate after dialysis (organic matter is isolated)

  16. Permeate after dialysis MWCO of Dialysis bags:3.5K Da

  17. Feed water: Schie canal water (Delft, NL)

  18. Composition of backwash solutions

  19. Impact of organic matter(flux:120 lmh) No pre-treatment! No in-line coagulation!

  20. Effect of backwash solution on membrane surface charge • Two types of backwash solution were used in this study • Milli Q water • UF permeate

  21. Measurement set-up Along fiber Through pore Wilbert van der Ven et al. 2008

  22. Measurement method 1 mM KCl solution was used in this study as background electrolyte solution

  23. Streaming potential of membrane • Backwash with permeate Streaming potential were measured before and after 14 filtration cycles. One cycle consists of 15-minute filtration at a flux of 120 lmh and 1-minute backwash at a flux of 240 lmh

  24. Streaming potential of membrane • Backwash with Milli Q water

  25. Conclusions • Backwashing with demineralized water is more efficient than UF permeate on fouling control • Both Ca and Na in backwash water contribute to the fouling of UF, probably by maintaining the bridge effect or decreasing the zeta potential of the membrane and the foulant • Organic matter in backwash water does not influence the fouling control of the UF membranes • Backwashing with pure water can maintain the negative charge of membrane

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