Application of Geothermal Energy for Brackish Water Desalination in the South of Tunisia

Abstract

In arid areas of Tunisia potable water is very scarce and the establishment of a human habitat in these areas strongly depends on how such water can be made available. On the other hand, these regions have important resources of underground brackish (salinity more than 3g/l) and often geothermal (temperature between 40?C and 90?C) water. Hence, these resources and can not be used directly.
Brackish water desalination is one of the ways to provide water in these regions for drinking and irrigation purposes. On the other hand, the conventional desalination technologies are not adapted for this situation. In fact, the investment and operating costs are so high that the recourse to this solution is justified only for large scale utilization. Moreover, the conventional energy supply of remote areas presents technical and economical problems. In this case, production of fresh water using desalinations technologies driven by renewable energy sources (solar, wind, geothermal, etc.) can be promising.
Since the brackish water is often geothermal in the south of Tunisia, and the water demand is low, the use of geothermal energy for water desalination can be promising.
In this paper we present a state of the art on using renewable energy sources, notably geothermal, for brackish and seawater desalination in the world and in Tunisia. An example of coupling an innovant desalination unit including horizontal-tubes falling-film evaporator and condenser, made of polypropylene with a geothermal spring is presented. The advantage of this plant is that it is made from cheap materials (polypropylene) allowing the use of low temperature energy (60?C to 90?C), which corresponds to the geothermal water temperature in the south of Tunisia. Moreover, the plant can be used for geothermal water cooling before utilization for irrigation or drinking.