Patent ID: 7988859

Claim:
A module, comprising: a first input port for receiving an input solution; a first mixer for mixing the input solution with a recycled solution from a second input port to produce a first mixed output; a stage I filter for concentrating the first mixed output to produce stage I retentate, wherein stage I permeate exits the module from the stage I filter via a first output port; a second mixer for mixing the stage I retentate from the stage I filter and an optional buffer solution from a third input port to produce a second mixed output; and a stage II filter in series with the stage I filter for concentrating the second mixed output to produce stage II retentate which exits the module from the stage II filter via a second output port, wherein stage II permeate exits the module from the stage II filter via a third output port, wherein the input solution from input port flows through the stage I filter and the stage II filter in a single pass, and recycled solution from the third output port flows countercurrent to the input solution into the second input port.