1. Introduction to Filtration
Chapter 31

2. Principles of Filtration
Filtrate (permeate) – is the fluid and particles that pass through the filter
Retentate – is the material trapped by the filter
Basic set up:
Filter and filter support
Vessel for filtrate
Driving force for the filtration

3. Issues with filtration
Clogging
Extractables – impurities from the filter
Binding
Adsorption – component binds to the surface of a medium
Absorption – liquids are taken up into the entire depth of the material (sponge)

4. Types of filtrations and filters
Macrofilters (filters, depth filters) – used to separate particles of m10 m or larger
Microfilters are used to separate particles from 0.1 mm to m10 m. Bacteria and cells
Ultra filters are used to separate macromolecules on the basis of their molecular weight (proteins)

5. Macrofiltration
Known as depth filters because they trap material throughout their depth.
Filters
Quantitative grade leave little ash when burned
Qualitative grade leaves significant ash when burned
Hardened grade are stronger than other filters to aid in vacuum filtrations

6. Microfiltration
Microfilters are called membranes and are manufactured to have a particular pore size.
Pore size (absolute) means that 100% of particles above that size will be retained by filter
Pore size (nominal) 90-98% retention.

7. Factors in choosing microfilter
Pore size
Resistance to organic solvents
Surface smoothness (smooth for micro scope)
Extractables
Wetting properties (hydrophilic or phobic)
Rate of flow, resistance to heat and tear

8. Applications of microfiltration
Removal of bacteria, yeast, and fungi to aid in sterilizing of liquids and gases
May remove mycoplasma, E. coli, fungi, yeast
May be used to monitor coliform bacteria in drinking water

9. HEPA Filters
HEPA – High Efficiency Particulate Air filters are used to remove particulates including microorganisms from air
Are depth filters made of glass microfibers that form a flat sheets are pleated to increase overall surface area.
May be used to protect lab animals from infections

10. Ultrafiltration
Ultrafilters are membranes that separate samples on the basis of molecular weight
Size is 1 to 100 Angstroms
Weights of 1000 to 1,000,000
Molecular weight cutoff, MWCO- is the lowest molecular weight solute that is generally retained by the membrane

11. Applications of ultrafiltration
Fractionation is the separation of larger particles from smaller ones
Proteins of different sizes
DNA from nucleotides
Concentration – solvent is forced through a filter while solute is retained.
Initial volume is reduced and high molecular weight species are concentrated above the filter

12. Dialysis and Reverse Osmosis
Are separation processes that use membranes similar to ultrafiltrtion
Dialysis is based on differences in the concentration of solutes between one side of the membrane and the other.
Driving force is the difference in solute concentration
Desalting is an example of this technique

13. Continued
Reverse Osmosis, RO – is used to remove very low molecular weight materials, including salts, from a liquid, (usually water).
RO is important in water purification systems
In RO, water under pressure flows through a thin film. Water goes through impurities don’t

14. Filtration Systems Small Scale Large scale Syringe filter devise
Spin filtration
Large scale
Hollow-fiber ultrafilters
Tangential or cross-flow filtration