The membrane performance is monitored by measuring several parameters to react on membrane blockage, evaluate element aging and identify early failures. As even slight changes in one parameter can have a significant influence on other parameters, they need to be normalized – compared to the initial membrane performance. In the example the not normalized permeate flow seems to be steady and that no further action needs to be taken. But the temperature is increasing which has an influence on the permeate flow. Considering the permeate under the same conditions – same temperature - the normalized permeate flow is decreasing over time.

In the spiral-wound membrane configuration, a flat sheet membrane and a feed channel spacer are wound around the permeate collection tube – the perforated central tube – to produce flow channels for permeate and feedwater.

The feed solution travels through the flow channels tangentially across the length of the element. Filtrate smaller than the molecular weight cut-off will then pass across the membrane surface into the permeate spacer, where it is carried down the permeate spacer towards the permeate tube. The remaining feed then becomes concentrated at the end of the element.

This design maximizes flow while minimizing the membrane module size.