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potable water. The water to be treated passes through a set of evaporators in series. The steam from one cell is used to evaporate the water in the following, while the primary energy input is to the first stage. Typically, MED systems have multiple chambers and hot steam from a nuclear power plant is carried into the chamber through pipes, repelling seawater on the pipes. Another method would be electrodialysis (ED) in which an electric field is used to separate any dissolved salts from water. The process involves the use of ion- selective membranes that allow either positive or negative ions to pass through while retaining the opposite ions. Electrodialysis has many applications, including desalination, table salt production, wine stabilisation, whey demineralisation, and pickling bath recovery. What does a desalination plant for a city look like? Spain is the world’s fifth largest producer of desalinated water, with 770 large-scale desalination plants, 99% of which are high capacity installations. A good example would be the Valdelentisco Desalination Plant in Murcia, Spain, which uses pumps to move water from the raw water tank to sand filters. The water is then passed through cartridge filters made of rubber-coated carbon steel, which filter the water through polypropylene ore size 5µm. In Sydney, Australia, seawater is drawn from the Tasman Sea through four intake pipes on the seabed, about 25 m below the water level. At full capacity, the intake pipes
deliver about six hundred million litres of seawater daily to the plant via a 2.5 m diameter concrete tunnel. Drum screens are used to remove any large materials that may enter through the intake tunnel. The plant’s pre- treatment filter system removes any solid material, such as algae and small dirt particles to get the seawater as clean as possible before the reverse osmosis process. The seawater is filtered through layers of filter coal and sand to prepare it for the reverse osmosis process. The clean filtered seawater passes through 36 000 reverse osmosis membranes so any
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Issue 1– 2024
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