SELEMION type of ion-exchange membrane and its related technology, developed originally by Asahi Glass after years of research and development. There are two types of ion--exchange membranes: anion--exchange and cation--exchange membranes. These membranes are films which are 100-200 micron meter in thickness, having ion passing pores of a few Angstrom in diameter, in which fixed ion of anion or cation are introduced.