Here you find some terms explained, which you hear from time to time in the membrane environment.

Flux is the permeate flow rate Q_P per membrane area A:

The concentrate containing compounds, which are rejected by the membrane.

Transmembrane pressure is the average driving pressure through the membrane. For pure water there is a linear relationship between transmembrane pressure and system flux. For feed material the flux increases with increasing driving pressure until the flux becomes limited by a gel layer on the surface of the membrane.

The dp is created by the crossflow over the module. It is defined as the difference between inlet pressure (P1) and outlet pressure (P2):


Crossflow is the liquid flow tangential to the membrane surface. It creates a shear force to reduce concentration polarization and fouling on the membrane.

The VCR in a batch process is defined as the ratio of feed and retentate volume:


The rejection coefficient is defined as the separation effect on the membrane for a solute i:


Diafiltration is the process of diluting the retentate to lower the concentration of molecules which can pass through the membrane. It allows further purification of the retentate or to increase the permeate yield.

Cleaning in place is a procedure for removal of foulants from the system without dismantling it.

CWF is the water flow through the membrane at defined operating parameters (pressure, temperature, water quality). It is used to evaluate the cleaning efficiency after the CIP.