Ultrafiltration: Mode of operation

1
Ultrafiltration Mode of operation

• Batch concentration
• Single-stage continuous concentration
• Multi-stage continuous concentration
• Batch diafiltration
• Continuous diafiltration

2
Batch concentration

• Most common mode of operation for concentration
• Ultrafiltration is usually operated at constant
  transmembrane pressure
• TMP generated by using a pressurising valve on
  the retentate line
• Filtrate (or permeate) is usually discarded while
  the retentate is sent back to the feed tank
• Feed concentration increases with time

3
Continuous concentration

• Not widely used in the bioprocess industry
• Main limitation is the low degree of
  concentration
• Continuous mode is used only when a solution is
  to be slightly concentrated
• Continuous concentration can be carried out using
  multi-stage process

4
Diafiltration

• Removal of low molecular weight solutes from
  macromolecule solutions
• Also used for buffer exchange
• Carried out by keeping the macromolecule
  concentration constant
• Most common and simple mode of operation is batch
  diafiltration
• Continuous diafiltration is possible using
  multi-stage operation

5
Microfiltration

• Microfiltration separates micron-sized particles
  from fluids
• MF modules are similar to those used in
  ultrafiltration
• MF membranes are microporous
• Retain particles by a purely sieving mechanism
• Typical permeate flux values are higher than in
  UF
• TMP is lower
• The various applications of microfiltration
  include
• Cell harvesting from bioreactors
• Virus removal for solutions
• Clarification of fruit juice and beverages
• Removal of cells from fermentation media
• Water purification
• Air filtration
• Sterilization

6
Microfiltration equations
7
MF Mode of operation

• Most frequently carried out in the dead end mode
• Dead ended mode gives low hold-up volume on the
  feed side
• Major problems include blocking of pores by
  particles
• Problems associated with the dead-ended mode of
  operation can be overcome using the cross-flow
  mode

8
Dialysis

• Mode of solute transport is diffusion
• Separation occurs because small molecules diffuse
  more rapidly than larger ones
• Degree to which the membrane restricts transport
  of molecules usually increases with solute size
• Applications of dialysis include
• Removal of salts and low molecular weight
  compounds from solutions of macromolecules
• Concentration of macromolecules
• Dialysis provides a tool for controlling the
  chemical species within a reactor
• Purification of biotechnological products
• Haemodialysis

9
Dialysis equation