New plant desalts well water using the reverse osmosis process, powered by solar thermal energy

Work on the solar thermal water desalination plant in Zarzis is finally coming to an end, a year after it began. The plant was inaugurated at a ceremony attended by Riadh Ben Khalifa, Managing Director of Solartech-sud, which is leading a regional project entitled “Creation of a manufacturing activity for thermal water desalination mini-centres using renewable energies to promote sustainable industrial and agricultural development in the region”. The plant, commissioned as part of this project, is located in the Miladi organic oil mill, which produces and sells organic olive oil certified by internationally recognised control bodies.

The new plant is called “Desaltec-z1”. It desalts water from a well. “The oil mill will use 73% of the water to be treated, while the remainder, which represents a very small proportion, will be recycled and treated”. The desalination plant has a capacity of 3.1 m3 of water per hour, for 4.2 m3 of water per hour taken from the well, giving an efficiency rate of over 73%. The water desalination process used at the Zarzis plant is reverse osmosis.

This process is based on the principle of salt-water separation using a semi-permeable membrane that needs to be changed periodically. “The water desalination plant, powered by solar thermal energy, consumes just 2 kWh of electricity per 1 m3 of water, reduces the salinity level by 90% (from 8.9 grams per litre to 0.7 grams per litre), can be controlled and started up remotely, and effectively manages brine discharges”, says the Regional Support Initiative for Sustainable Development (Irada) in Tunisia.

For the record, the Zarzis desalination plant project was the brainchild of Ahmed Friaa, the former director of the National School of Engineers in Tunis, and implemented by seven Tunisian engineers under the supervision of Samir Hamza, professor of mechanical engineering and director of the National Institute of Applied Sciences and Technology (Insat) at the University of Carthage, and Riadh Ben Khalifa, lecturer in contemporary history (HDR) at the University of Tunis. In 2017, the invention was patented by the Institut national de la normalisation et de la propriété industrielle (Innorpi), a public body under the authority of the Tunisian Ministry of Industry.

Also in 2017, an initial experimental plant using solar thermal energy was developed, but it did not go into production because the actual yields were not yet satisfactory”, reveals Walid Keskes, one of the stakeholders in the desalination project.