Brackish water desalination using renewable energy

Drinking water is scarce in southern Tunisia due to low rainfall, and high salinity in the available groundwater resources. The National Water Quality Improvement Program (PNAQ) is intended to remedy the situation. The National Water Utility SONEDE relies on desalination plants operated by renewable energy. GKW Consult, a company of Tractebel, evaluated the first phase of the project and provided a feasibility study for the second phase.

National Program to improve water quality

The first phase addressed regions with groundwater salinity of over 2 g/l. Ten desalination plants are meanwhile under construction. The second phase focussed on regions with allegedly lower salinities. During the study, GKW Consult experts detected, however, that the actual salinity in these regions is up to 10 mg/l. Due to these results, the construction of six brackish water desalination plants is now intended. Over 500,000 inhabitants in five governorates will benefit from this project.

Desalination process using renewable energy

To assess the available water resources, GKW Consult performed a hydrogeological study. The experts also identified new brackish water resources to cover the demand until 2035. In addition, GKW Consult analysed different technologies to identify the optimum combination of renewable energy and various desalination processes. Photovoltaic and wind turbines proved to be the best options. In this project, Lahmeyer International supports its subsidiary with a wind potential assessment based on modelled data from the existing wind map of Tunisia and a recommendation of a suitable location for a wind energy plant.

High-yield plants

The team also investigated which of the intended sites would be the best for using renewable energy based on climatic data and the levelized energy cost (LEC). The experts favour Ben Guerdene in the governorate of Medenine. To prove the theoretical assumptions of the feasibility study and to obtain more accurate data, Lahmeyer is currently perfoming wind measurements. After their finalization in May 2018, the company will recommend an appropriate wind power plant and create an energy yield assessment on the Ben Guerdene wind park.

Competitive desalination plants

In addition, the feasibility study examined whether the intended plants could be operated competitively. GKW Consult found out that desalinated drinking water could be produced at a competitive cost with the use of renewable energy. The results convinced SONEDE to continue on this path, even if the cost for energy from renewable sources is still equal to, or even slightly higher than that for energy from conventional sources.

GKW Consult also supports the project beyond the study phase. The follow-up project comprising final design, construction and technical support for the six desalination plants has already started. The plants are to be commissioned in 2022.