Filtration with internal fouling control

A filtration process for the separation of a filterable fluid stream by a spiral wound filtration membrane module into a permeate stream and a retentate stream which process comprises:

• (a) flowing a feed stream to be separated at a feed stream flow rate into a feed stream inlet and axially across a retentate side of a spirally wound membrane under positive pressure in a first flow direction through a retentate channel of the membrane module;
• (b) withdrawing an axially flowing retentate stream at a retentate outlet of the membrane module;
• (c) collecting a permeate stream flowing radially within a permeate channel located on a permeate side of the membrane that is opposite to the retentate side thereof, in a permeate collection tube in fluid communication therewith, wherein the collection tube contains at least one flow resistance element;
• (d) flowing collected permeate stream through the central permeate collection tube to a permeate outlet for discharge from the module;
• (e) returning a portion of the permeate discharged from said permeate collection tube to a permeate inlet thereof at a permeate flow rate;
• (f) adjusting the flow rate of the permeate stream to provide baseline pressures at the inlet and the outlet on the permeate and retentate sides of the membrane such that the difference in baseline pressures between the permeate and retentate sides of the membrane is substantially the same at the inlet and the outlet, wherein the baseline pressure on the permeate side of the membrane is greater at the inlet than the baseline pressure at the outlet and the baseline pressure on the retentate side of the membrane is greater at the inlet than the baseline pressure at the outlet;
• and
• (g) periodically performing a rUTMP process on said permeate side of the membrane, by either increasing the permeate pressure or decreasing the retentate pressure, resulting in a controllable overpressurization on the permeate side of the membrane in comparison with the pressure on the retentate side of the membrane to provide backflow across the membrane while axial flow is maintained from the inlet to the outlet on both sides of the membrane, wherein difference in pressures between the permeate and retentate sides of the membrane is substantially the same at the inlet and the outlet during said rUTMP process.