desalination
desalination
process of removing soluble salts from water to render it suitable for drinking,
irrigation, or industrial uses. In distillation, salt water is heated in one
container to make the water evaporate, leaving the salt behind.
The desalinated vapor is then condensed to form water in a separate container. The high fuel costs involved in vaporizing salt water can be reduced by using a vacuum to lower the boiling point or by exposing a water spray or film to high heat, a process known as flash distillation.
In Hawaii the vacuum method also produces electricity in a process that vaporizes warmer, near-surface water, uses the steam to run a turbine, and condenses the steam with cold water from the ocean depths.
Other desalination techniques includ¨:
 | electrodialysis,the use of porous membranes to filter out negatively and positively charged salt ions; |
| freezing, based on the principle that water excludes salt when it crystallizes to ice; |
| and reverse osmosis, in which pressure, generated by the
presence of salt in the water, forces water through a membrane permeable
only by pure water. |