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Ultrafiltration fouling control

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Ultrafiltration fouling control Demineralized water backwashing Sheng Li Sanitary Engineering, Delft University of Technology The Netherlands * * Backwash solutions ... – PowerPoint PPT presentation

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Title: Ultrafiltration fouling control


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 bags3.5K Da
17
Feed water Schie canal water (Delft, NL)
Water quality parameter Feed
Ca2 (mg/l) 101
Na (mg/l) 58.57
Conductivity (µs/cm) 836
Turbidity (NTU) 4.5
DOC (mg/l) 20
18
Composition of backwash solutions
Ca2 (mg/l) Na (mg/l) DOC (mg/l)
UF permeate 100 58.56 18.65
UF permeate after dialysis 20 8.7 17
Demineralized water lt1 lt1 0.5
19
Impact of organic matter(flux120 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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