The work and the technique: desalination plan Shoiaba 3 expansion II, Saudi Arabia

The Shoaiba 3 Expansion II project was contracted to Fisia Italimpianti, part of the Webuild Group. The main challenge was dictated by the time required by the client; in fact, the work was completed in 21 months. 

The plant is located in an area with numerous older thermal desalination plants and produces 250,000 m³/day of drinking water. It uses reverse osmosis technology, which is clearly preferable both for the environment, as it avoids raising sea temperatures, and in terms of energy consumption.

Reverse osmosis is a process of removing the salt component from seawater that is accomplished in several steps. Water is initially taken from the sea and sent to the first module where it undergoes algae, oil and grease removal and pressure filtration treatment. It is then fed into the reverse osmosis system and conducted by high-pressure pumps (up to 80 bar) through membranes to remove salts. The now desalinated water is finally enriched with minerals and disinfected to be potable.

For the execution of the project, after an initial preliminary phase supporting the environmental impact study, intervention works were carried out in the marine area, with particular attention to the environment and the coral reef, which was already stressed due to the activity of the thermal plants.

Two suction pipes over 550 metres long and a 470-metre outlet were later built to return the resulting brine to the sea. The pipes were installed by excavating on the seabed so that water could be drawn from deeper layers, where it contains fewer impurities and is not contaminated by oils that could damage the filtration membranes.

At the same time, the pumping station was built, which, given the depth of the location, required preventive protection with drying piles and a concrete plug at the bottom to prevent groundwater from re-entering the excavation.

Finally, the plant was constructed where pretreatment, reverse osmosis and re-mineralization treatment activities take place.