**1. Introduction**

In recent decades, humanity has become more and more aware of the danger threatening the planet as a result of the great demographic growth and the enormous technological advances which generate unsanitary conditions of the environment. Water is a big problem today affecting the whole of the earth. To do this, it must then be preserved by all possible means: reduction of waste; reuse of wastewater and its introduction into special recycling techniques. The reuse of wastewater is a widely used practice in regions of the world affected by water resource shortages. The Mediterranean Basin is one of the regions of the world where the reuse of urban effluents is practiced at a low rate.

In Algeria, this area is not very developed, and the system put in place does not allow the desired prospects to be achieved to deal with the problems emanating from wastewater. Several regions of the Algerian Sahara where wastewater discharged into nature without prior treatment with large and increasing volumes which are sources of pollution. They generate many water-borne diseases and the spread of epidemics [1]. The Algerian authorities have agreed to plan several purification stations, with a view to eliminating pollution and the risks of contamination in urban areas. Protecting the receiving ecosystem and the water supplies of these regions of the Algerian Sahara, in particular the water table, the possibility of reusing filtered effluent for irrigation, becoming an important biodiversity area and a breeding ground [2].

This chapter, aiming to shed light on the wastewater treatment component in the Algerian Sahara, through a description of the different systems used and to discuss their reliability and constraints.
