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FEATURE STORYAugust 30, 2022

Tunisia: Recycled Wastewater Cleans Up the Sea, Provides Water for Farming


  • Piping wastewater under land and sea creates an environmentally safe disposal system north of Tunis and cleans up beaches.
  • Thus, samples of seawater show 96% met the levels of bacteria that health authorities view as safe and 97% complied with safe concentrations of detergents.
  • Expanding the availability of treated wastewater for farming as well as urban spaces helps water-poor countries like Tunisia adapt to the increase in water scarcity that has been brought on by climate change.

The above “before” and “after” photos say it all—a river of blackened sludge used to pour into the Mediterranean Sea, contrasting with, five years later, a clear turquoise sea and clean, sandy beach. For the first time in years, in 2020, Tunisia’s health authorities opened Raoued Beach just north of Tunis for swimming, giving the local economy a boost. Fishermen echoed their approval for the changes they saw in the marine environment.

What looks like a miracle was in fact the diligent work of engineers and scientists to clean up the water. 96% of a batch of samples of seawater collected at Raoued in 2020 complied with levels of bacteria considered safe for public health; 97% for the level of detergents. These improvements were the result of channeling treated wastewater underground through pipes to a submarine outfall—the technical term for a pipeline under the sea—stretching 6 kilometers offshore before discharging its effluent 20 meters down the surface. At this depth, farther out in the Gulf of Tunis, treated human sewage and other liquid waste disperses, diluting the pollution associated with daily modern domestic life and farming methods. 

Cleaning the wastewater for reuse on land also expands Tunisia’s capacity to adapt to the increasing water scarcity the country has been experiencing as a result of climate change. Investing in a new, environmentally safe system for disposing of treated wastewater preserves the country’s lovely Mediterranean coastline and benefits communities that reside, work, and play along it.

Tunisia is one of the most water scarce countries in the world. In 2017, 367 cubic meters (m3) of water were available per capita to its almost 12 million inhabitants, compared to a regional average of 526 m3 and a global average of 5,700 m3. Urban growth, rising demand, and the need to support employment in rural areas with irrigation, were adding pressure. 


Poorly treated wastewater being channeled to the sea before the project.


Channeling treated wastewater underground protects the environment and prevents its contamination.

Its coastal and marine ecosystems were being threatened by pollution from agricultural drainage and municipal discharge. When the Gulf of Tunis was identified as the biggest pollution “hot spot,” the government made it a priority. The National Sanitation Utility (ONAS) and government ministries developed a program aimed to address this challenge. 

A poorly maintained, 30-year-old sewage system that was in place could no longer cope with the volume of waste being generated. Open and above ground, its channels carried wastewater from the Chotrana treatment plant, just south of Raoued, to the El Khelij river, discharging it as the river hit the beach. People complained about the smell and dangers to health. Visible filth hindered the area’s potential for tourism and other development. Even though it was treated, the quality of the wastewater was too poor for agriculture. 

Wastewater is safe for reuse

The improvements are the result of a US$60.6 million project that was completed in 2021. The Northern Tunis Wastewater Project, funded by the World Bank and co-financed with a grant from the Global Environment Facility (GEF), supported the construction of the underground channels and outfall, and of a wastewater storage basin.   

It funded the two parallel, impermeable pipes that funnel wastewater from the Choutrana plant to a large split-storage sludge basin nearby at El Hissiene, where wastewater separates into liquids and solids. Submerging the pipes prevents wastewater from contaminating the surroundings before it is treated and stops it from being re-contaminated afterwards. 

From the basin, its flow can be regulated for irrigation, making millions of cubic meters of good quality, recycled water available to about 500 farmers in Borj Touil. And, with rapid urbanization and changing land use in the area, ONAS has reached an agreement for urban developers to use some of the wastewater to irrigate green areas of the newly developed Tunis Bay City.

El Hissiene basin regulates the flow of treated wastewater to the submarine outfall.

To show the public that recycled wastewater is safe for growing plants, plots belonging to three farmers in Borj Touil have been irrigated with treated wastewater, and more demonstration plots have been set up near a water treatment facility at Sidi Amor, on the coast north-west of Borj Touil. Sidi Amor has filtration systems, water tanks, a pumping station and irrigation system, a laboratory, and demonstration center. The Sidi Amor pilot project has helped improve coordination between various stakeholders, and its quality control laboratory is open to agricultural students. 

Construction of a greenhouse for the agricultural development group of Sidi Amor.

Purified water supplying the farmers' agricultural plots

Treated water quality at the entrance of the maturation pool.

Separately, the water utility firm and ONAS now have a modernized billing system, streamlining revenue collection. ONAS’s IT system has been upgraded to include computer-based analysis of real-time data, making it possible to manage wastewater flow remotely and more efficiently.


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