Ultrafiltration fouling control

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Ultrafiltration fouling control

• Demineralized water backwashing

Sheng Li Sanitary Engineering, Delft University
of Technology The Netherlands
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Content

• Introduction
• Hypotheses
• Results
• Conclusion

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

• Divalent ions
• Monovalent ions
• Organic matter

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Hypotheses of NOM fouling

• Ca-bridging effect and/or Ca complexation
• Charge screening effect (DLVO theory)
• NOM molecule adsorption

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Ca-bridging effect(filtration)
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Ca-bridging effect(Backwash with permeate)
Ca
Ca
Ca
Ca
Ca
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Ca-bridging effect(Backwash with demi water)
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Charge screening effect(filtration)
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Charge screening effect(Backwash with permeate)
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Charge screening effect(Backwash with demi water)
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Results(Impact of calcium, flux 85 lmh)
No pre-treatment! No in-line coagulation!
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Results(Impact of sodium, flux 85 lmh)
No pre-treatment! No in-line coagulation!
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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

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Backwash solutions

• Demineralized water
• UF permeate
• UF permeate after dialysis (organic matter is
  isolated)

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Permeate after dialysis
MWCO of Dialysis bags3.5K Da
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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
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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
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Impact of organic matter(flux120 lmh)
No pre-treatment! No in-line coagulation!
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Effect of backwash solution on membrane surface
charge

• Two types of backwash solution were used in this
  study
• Milli Q water
• UF permeate

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

• 1 mM KCl solution was used in this study as
  background electrolyte solution

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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
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Streaming potential of membrane

• Backwash with Milli Q water

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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