*3.1.1.3 Ion exchange membranes*

Membranes are classified as anion exchange membrane (AEM) if the polymer matrix is embedded with fixed positive charge groups, and vice versa, for cation exchange membranes (CEM) [51], which involves the permeation of anions/cations, and rejection of cations/anions in the effluent. Electrodialysis (ED), reverse electrodialysis (RED), diffusion dialysis (DD) and the Donnan membrane process (DMP) are examples of such, which usually involves the exchange of ions between solutions across the membrane as shown in **Figure 3**. The application of these processes is usually based on the type of effluent which is usually reported as an energy resourceful mechanism of separation by potential gradient.
