Filtration allows for the exclusion of organisms based upon size. There are many types of filtration techniques, but when sterilizing a system membrane filtration is used. Membrane filtration traps contaminants larger than the pore size on the surface of the membrane. If contaminants are smaller than the desired particle, decrease the membrane pore size and trap the product while passing the contaminants through the membrane. For greater system flexibility, filters can be added in parallel or series. When adding a filter of same pore size, in parallel, throughput increases. If instead a filter of differing pore size was added in series, separation of multiple microorganisms are possible.

Here is a diagram of the separation of particles through the use of a membrane.

Absolute sterilization - separates particles based on size
Used for heat sensitive media
Removal of multiple particle sizes
Allows for fairly high throughput

Each filter has a specific nominal pore size
Unable to separate microorganisms that have the same size
May require a high differential pressure
Produced by Scott Ogoreuc and Greg DiLeo