Basic concepts of membrane filtration : Rejection and Fouling

Rejection: How much solutes are rejected by the membrane is defined as the solute rejection of a membrane.

Rejection coefficient of a specific salt (NaCl, MgCl, CaCO₃) can be calculated using below equation

Salt rejection coefficient R;

where, Cji0 and Cji respectively, are the salt concentrations on the feed and permeate sides of the membrane

Fouling: Fouling is the precipitation of unwanted materials on the membrane, during the membrane filtration. Fouling is categorized based on the material which is available in the feed waters; i.e.

Scaling (inorganic fouling)........compounds CaCO₃, MgCO₃

Organic fouling..........................humic substances

Colloidal fouling........................colloids such as silica substance

Bio fouling.................................the growth of bacteria on the membrane surface.

Effects of fouling;