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WaterWare On-line Reference Manual
DesalinationMore than 7,500 desalination plants are in operation worldwide. About 60% of them are located in the Middle East. The world's largest plant in Saudi Arabia produces 600,000,000 m³ per day of desalted water. About 12% of the world's capacity is produced in the Americas, with most of the plants located in the Caribbean and Florida.
Desalination TechnologiesDesalination removes dissolved minerals from seawater, brackish water, or treated wastewater. A number of technologies have been developed for desalination, including
A primary distinction is also the source of the water to be used: directly from the ocean or estuaries, brackish groundwater, or treated wastewater. Reverse OsmosisIn RO, feedwater is pumped at high pressure through permeable membranes, separating salts from the water. The feedwater is pretreated (filtered) to remove particles that would clog the membranes. The quality of the water produced depends on the concentration of salts in the feedwater, the pressure (and thus energy expended) and the salt permeation constant of the membranes. Product water quality can be improved by adding a second pass of membranes, whereby product water from the first pass is fed to the second pass.DistillationIn the distillation process, feedwater is heated and then evaporated, leaving the salts in the feedwater. The most common methods of distillation include
Water QualityDistillation plants produce a high-quality product water that ranges from 1.0 to 50 ppm TDS, while RO plants produce a product water that ranges from 10 to 500 ppm TDS. The WHO drinking water standard is at 500 ppm. For domestic, that is drinking water use, post-treatment processes like chlorination are often employed to ensure that product water meets the health standards for drinking water.Desalination product water may be used in its pure form (e.g., for make-up water in power plant boilers) or it may be mixed with less pure water and used for drinking water, irrigation, or other uses. The desalinated product water is usually more pure than drinking water standards, so when product water is intended for municipal use, it may be mixed with water that contains higher levels of total dissolved solids. Pure desalination water is highly acidic and is thus corrosive to pipes, so it has to be mixed with other sources of water that are piped onsite or else adjusted for pH, hardness, and alkalinity before being piped offsite. Energy use and costs
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