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Ultrafiltration membrane: Porous membrane with the pores as a rule in the range 20 - 100 nm used in baromembrane process of ultrafiltration.

Ultrafiltration: Pressure-driven membrane-based separation process in which particles and dissolved macromolecules smaller than 0.1 µm and larger than about 2 nm are rejected.

Uphill transport: Process in which diffusion of a component occurs from a less concentrated feed stream to a more concentrated permeate stream

Upstream or Feed stream: The stream of the mixture to be separated directed into upstream part of the membrane.

Upstream: Side of a membrane into which penetrants enter from the feed stream.