The main purpose of ultrafiltration is not for exchange of oxygen or nutrients or even the removal of waste products. These are of negligable importance. The primary purpose of ultrafiltration is really for the maintainance of the plasma and intersitial fluid volumes.

Ultrafiltration water treatment utilizes a semi-permeable membrane to ... Membrane cleaning may be achieved by allowing a very small portion of the flow to exit ... Filtration can also be carried out from the "outside-in" .

Philip George Newick has written:

'Ultrafiltration'

For insoluble impurities a method is ultrafiltration.

To purify whatever your filtering to absolute extent, to rid it of everything until its absolutely clean.