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The sixth lecture in the module Particle Technology, delivered to second year students who have already studied basic fluid mechanics. …

The sixth lecture in the module Particle Technology, delivered to second year students who have already studied basic fluid mechanics.

Membranes and Colloids covers the different types of particle related pressure driven membrane separations and models of flux decay and fouling. Colloidal behaviour using the DLVO theory is also covered, including colloid stability.

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  • 1. Membranes & Colloids
    Chapters 4 & 13 in Fundamentals
    Watch this lecture at http://www.vimeo.com/10202852
    Visit; http://www.midlandit.co.uk/particletechnology.htm for further resources.
    Course details:
    Particle Technology, module code: CGB019 and CGB919, 2nd year of study.
    Professor Richard Holdich
    R.G.Holdich@Lboro.ac.uk
  • 2. Membranes & Colloids
    • Types, configurations and permeate flux
    • 3. Surface and internal fouling
    • 4. Polarisation flux models & enhancement
    • 5. Colloidal interaction – DLVO theory
  • Introduction
  • 6. Particle size - colloids
    • Bacteria 0.2 to 8 microns
    • 7. viruses 0.05 to 0.5 microns
    • 8. colloidal silica 0.02 to 1 micron
    • 9. macromolecules 0.01 to 0.5 microns
    • 10. ions <0.01 microns
    • 11. no concentration limit in MF & UF processes
  • Membrane types
    • Microfiltration
    • 12. 0.05 to 10 microns generally
    • 13. Ultrafiltration
    • 14. 1 to 50 nano-metres
    • 15. Nanofiltration & Reverse Osmosis
  • Membrane cartridges
  • 16. Cells - unstirred and stirred
  • 17. Filter Media - Pressure
    Medium
    Medium
    P
    P
    Rm
    Rm
    Po
    Po
    v1
    v2

  • Crossflow filtration
  • 19. Crossflow filtration
  • 20. Flux variation and resistance
    • Resistances to membrane filtration:
  • Flux variation and resistance
    • Darcy’s law:
    • 21. Darcy’s law modified:
  • Flux variation and resistance
    • Darcy’s law:
    Jis permeate flux, in conventional units of litres per metre squared of membrane area per hour. It is the same as superficial velocity.
  • 22. Crossflow filtration
  • 23. Permeate flux decay
  • 24. Filtration fundamentals
    Why can’t we simply measure Rm for each medium?
  • 25. Membranes & Colloids
    • Types, configurations and permeate flux
    • 26. Surface and internal fouling
    • 27. Polarisation flux models & enhancement
    • 28. Colloidal interaction – DLVO theory
  • Filter Media - Pore Size?
    • What do we mean by pore size?
  • Filter Media - Pore Size?
    Metal fibre microfiltration medium - rated at 3 microns
  • 29. Filter Media - Pore Size!
    • Equivalent pore size
  • Membrane media - PTFE
    0.2 micron rated membrane filter
  • 30. Membrane internal fouling?
  • 31. Membrane secondary membrane
  • 32. Membranes & Colloids
    • Types, configurations and permeate flux
    • 33. Surface and internal fouling
    • 34. Polarisation flux models & enhancement
    • 35. Colloidal interaction – DLVO theory
  • Membrane models
  • 36. Rejection
    R = 1 - Np/Nb
  • 37. Equilibrium flux response
  • 38. Membrane film theory
  • 39. Membrane simple circuit
  • 40. Membrane feed & bleed
  • 41. Diafiltration
  • 42. Diafiltration
    Stirred tank displacement washing only:
    e.g. washing times given a flux rate of 50 l m-2 h-1 and tank volume of 1000 litres
    Area (m2): 1 10 20
    t(hrs) C(ppm) C(ppm) C(ppm)
    0 500 500 500
    1 476 304 184
    2 452 184 68
    4 409 68 9
    6 370 25 1
  • 43. Membrane cleaning
  • 44. Membrane & other SLS
  • 45. Membrane surface filter
  • 46. Membrane surface filter - slots
  • 47. Membranes & Colloids
    • Types, configurations and permeate flux
    • 48. Surface and internal fouling
    • 49. Polarisation flux models & enhancement
    • 50. Colloidal interaction – DLVO theory
  • Colloidal interaction
    • Stokes’ law tells us about settling?
    • 51. Increase diameter but decrease density – net enhanced rate
    • 52. COAGULATION
    • 53. v
    • 54. FLOCCULATION
  • Colloidal interaction
    • Floc bed clarifier
  • Electrical interaction
    • Surface –ve charge
    • 55. Fixed layer +ve ions
    • 56. Diffuse layer after…
    • 57. Shear layer
    • 58. Zeta potential – measured by moving particle in field,
    • 59. Typically -50 to 0 mV
  • Van der Waal’s attraction
    where AH is the Hamaker* constant for a given system and
    Hs is the ratio of the separation distance (z) between the particles and
    the particle radius.
    So, in terms of particle diameter
    *5x10-20 J for water
  • 60. Electrical repulsion
    where the Zeta potential is used extensively above, together with the particle
    diameter, dielectric constant of the system and the Debye-Hückel function –which is a function of ionic conditions.
  • 61. Net forces - DLVO
    • Total
    • 62. Dimensionless interaction energy
    • 63. Force
  • Net forces - DLVO
    Which colloid is the most stable?
  • 72. Net forces - DLVO
    • Silting of estuaries
    • 73. Click image for XLS
  • Stokes’ settling equation
    • Colloid stability important in filtration and sedimentation.
    • 74. Often assessed by the Zeta potential
    • 75. Surface forces can predominate at iso-electric point.
  • Membranes & Colloids
    • Types, configurations and permeate flux
    • 76. Surface and internal fouling
    • 77. Polarisation flux models & enhancement
    • 78. Colloidal interaction – DLVO theory
  • This resource was created by Loughborough University and released as an open educational resource through the Open Engineering Resources project of the HE Academy Engineering Subject Centre. The Open Engineering Resources project was funded by HEFCE and part of the JISC/HE Academy UKOER programme.
    © 2009 Loughborough University
    This work is licensed under a Creative Commons Attribution 2.0 License.
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    The HEA logo is owned by the Higher Education Academy Limited may be freely distributed and copied for educational purposes only, provided that appropriate acknowledgement is given to the Higher Education Academy as the copyright holder and original publisher.