Types of Desalination

Multi-stage Flash
Multi-effect Distillation
Vapor Compression Distillation

Reverse Osmosis
Electrodialysis Reversal

Middle East Desalination

Huntington Beach Proposal

Sources Cited

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• A voltage is used to move salts through a membrane, leaving fresh water behind.

History of use
• Commercially introduced in the early 1960’s about ten years before reverse osmosis.
• Although originally was conceived as a seawater desalination process, it has been generally used as a cost-effective way to desalt brackish water.

• Electro dialysis depends on some general principles:

• Most salts dissolved in water are ionic, meaning they contain a positive (cation) or negative (anion) charge.
• These ions are attracted to electrodes with an opposite electric charge
• Semi-permeable membranes allow selective passage of either an anion or a cation but not both.

• Electrodes connected to battery are placed in container of saline water.
• As electrical current is applied through the solution, the ions (Na+, Cl¯, Ca²+, Carbonate ²¯ ) migrate to the electrode of opposite charge.
• Anions (Cl¯, Carbonate ²¯) travel opposite of current and pass through an anion semi-permeable membrane.
• Once through this their path is blocked by a cation semi-permeable membrane and is trapped.
• The same event happens to the cations, (Na+, Ca²+) which pass through a cation semi-permeable membrane and are trapped by an anion semi-permeable membrane.
• The result is two flows of fresh water and three flows of concentrated brine are formed.

• Automatic operation of the plant, requiring very little maintenance and supervision, except for membrane replacement.
• Very effective process to remove and purify salt concentrate as a valuable product.
• Applications in many commercial industries
o Cheese whey demineralization
o Tartaric wine stabilization
o De-acidification of fruit juices

• Pretreatment is required to prevent materials which could harm or clog membranes.
• Works most efficient in low-salinity applications
o Brackish water desalination
o Surface water desalination (streams)