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Project in Sfax transforms the Mediterranean into a direct supply source, with giant underwater pipelines, reverse osmosis technology, and a structure prepared to expand the production of drinking water in a region pressured by water scarcity.
The city of Sfax, in Tunisia, now has a desalination plant prepared to convert Mediterranean seawater into drinking water on an industrial scale, with an initial capacity of 100 million liters per day and a structure sized to double that volume.
With two large-scale underwater pipelines, each 4.2 kilometers long, the system transports saltwater from the offshore intake area to the onshore treatment unit, according to technical data released by Tedagua, linked to the executing consortium.
Planned to reinforce the supply of one of the country’s main urban regions, the project expands the role of desalination in an area pressured by water scarcity and reduces the exclusive dependence on continental water sources.
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In Sfax, this type of infrastructure serves as a complementary source to provide more stability to the supply, especially during periods of lower freshwater availability and higher demand on conventional capture and distribution networks.
Water capture in the Mediterranean
Although the onshore part concentrates filters, membranes, chemical systems, reservoirs, and pumps, the operation begins before reaching the plant, at the seabed, where the underwater lines capture the raw water to be sent for treatment.
The ducts were manufactured in HDPE DN1800, an acronym associated with high-density polyethylene used in large-diameter pipelines, capable of continuously transporting large volumes of saltwater to the intake chamber.
Upon reaching the reception structure, the water undergoes an initial mechanical screening before pumping, a stage that retains larger materials and helps protect sensitive equipment against obstructions during pre-treatment and membrane operation.
This maritime infrastructure ensures a permanent connection between the Mediterranean and the onshore plant, creating the necessary flow to maintain the expected daily production and sustain the planned supply for the Sfax region.
Reverse Osmosis at the Sfax Plant
After collection, the water goes through a sequence of physical and chemical processes before reaching the standard for human consumption, starting with a two-phase filtration, with sand and anthracite, in addition to cartridge filters.
This stage prepares the water for the main salt removal phase, as it reduces impurities and protects the membranes, components that need to operate with stability to maintain the efficiency of the desalination system.
Desalination occurs through reverse osmosis, a technology that separates water from dissolved salts using membranes subjected to high pressure, a process adopted in large seawater treatment plants.
At the Sfax unit, according to Tedagua, the system includes four reverse osmosis racks, energy recovery equipment, and a CIP unit, used for membrane cleaning during the plant’s operational routine.
As reverse osmosis depends on high pressure, energy consumption becomes one of the central points of the project, which explains the presence of systems aimed at reusing part of the energy involved in the process.
After salt removal, the water undergoes post-treatment to adjust its characteristics before distribution, with remineralization by carbon dioxide and calcite beds, as well as chemical treatment with hypochlorite and caustic soda.
Reservoir and Distribution of Potable Water
The treated water goes to a reservoir with a capacity of 25,000 cubic meters, equivalent to 25 million liters, which functions as a link between the plant’s continuous production and regular delivery to the public system.
From this point on, pumps drive the stored volume to the distribution network, allowing the plant’s continuous operation to be compatible with domestic, commercial, and urban consumption variations throughout the day.
The initial capacity of 100,000 cubic meters per day corresponds to 100 million liters daily, while the civil and maritime works were prepared for an expansion capable of doubling the production.
If the second stage is executed, the unit may reach 200,000 cubic meters per day, reinforcing the role of desalination as a strategic supply source for Sfax and for the population served by the system.
According to Tedagua, the infrastructure was designed to ensure potable water for more than 600,000 inhabitants, a number that helps to gauge the plant’s relevance in a region with strong urban demand.
Brine Disposal at Sea
In addition to capturing water from the Mediterranean, the project has a specific system for brine disposal, a concentrated waste generated when salts and dissolved components are separated from the water during reverse osmosis.
This waste travels through a 3.2-kilometer submarine outfall, also constructed in HDPE DN1800, responsible for conducting the brine back to the marine environment as per the technical design planned for the operation.
The management of brine is an essential part of a desalination plant because the process does not eliminate the salts removed from the water but concentrates them in a flow that needs to be disposed of in a controlled manner.
With capture, treatment, and discharge organized in complementary structures, the project goes beyond the installation of equipment on land and depends on engineering distributed between the marine environment, industrial area, and urban network.
International Consortium and Energy Infrastructure
Tendered by SONEDE, the national company responsible for water supply in Tunisia, the plant was executed by a consortium formed by Cobra Instalaciones y Servicios, parent company of Tedagua, in partnership with Orascom Construction and Metito Overseas.
To support pumps, filters, reverse osmosis systems, and chemical treatment, the project includes an electrical substation with two lines, a necessary component to maintain daily production with a stable energy supply.
The location in Sfax reinforces the importance of the project for an area with strong urban and economic significance, where water security solutions need to reduce exposure to drought periods and limitations of traditional sources.
In practice, the scale of the installation is evident both in the volume produced and in the extent of the submerged infrastructure, which brings water from the Mediterranean to the plant before returning it treated to the supply system.
In coastal cities subject to water stress, desalination has gained ground as an alternative to diversify supply, transforming the sea into an active part of the public network, and not just a geographic boundary.
With two submarine pipelines of 4.2 kilometers, a 3.2-kilometer outfall, a 25,000 cubic meter reservoir, and a designed capacity to reach 200 million liters per day, the plant places coastal engineering at the center of Tunisia’s response to water scarcity.
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