**Classification according to the geometry of the membranes**

According to the geometry under which the membranes are manufactured, they are classified as:


#### **Classification according to chemical nature**

The membranes are synthesized from inorganic materials and organic polymers. There are also mixed membranes made from inorganic materials and polymers [38].

**Figure 4.** *Flat module [36].*

**Figure 5.** *Spiral module [37].*

**Figure 6.** *Tubular module [36].*

**Figure 7.** *Hollow fiber module [36].*

The majority of usable membranes are manufactured either from inorganic materials or from polymers.

The main polymers used for the manufacture of membranes are:


Inorganic membranes are made of ceramic (zirconium, titanium, aluminum oxides). These membranes are expensive, have a mechanical, chemical and thermal stability superior to polymeric membranes, they are brittle [38].
