The following are commonly used modes of filtration.

1. Direct Flow Filtration (DFF): or “dead-end” filtration is where the feed stream is applied perpendicular to the membrane face, attempting to pass 100% of the fluid through the membrane.

2. Tangential Flow Filtration (TFF or crossflow filtration): also known as crossflow filtration is where the feed stream passes parallel to the membrane face as one portion passes through the membrane (permeate) while the other remainder (retentate) is recirculated back to the feed resrvoire. See outline

TFF: has been used in the separation of blood components (US 4,888,115), beer solutions (US 4,644,056), immunoglobulins from milk or colostrum (US 4,420,398) and bacterial enzymes from cell debris (Quirk, 1984, Enzyme Microb. Technol, 6(5): 201.

(a) High Performance tangential flow filtration (HPTFF): See outline