Friday, August 22, 2014

Desalination

Desalination, also called desalinization, is the removal of salt from seawater to make available more freshwater for human consumption.  Since only a tiny percentage of water on Earth is freshwater, and most of this is locked in glaciers, some arid areas bordering oceans or salt lakes view desalination as a necessity.  Israel gets over a third of its drinking water from desalination, and the amount of drinking water obtained from desalination worldwide is expected to almost double by 2020.

Desalination is possible through three main mechanisms.  First, simple solar distillation of seawater uses the different boiling points of pure water and salt to separate the two.  Water boils (evaporates) at 212 degrees Fahrenheit, while NaCl (sodium chloride, or the main salt in the ocean) doesn't boil or evaporate until 2,575 degrees Fahrenheit.  Since the sun warming seawater can get some water molecules to evaporate at a temperature lower than 212 degrees, water is collected on a clear plastic or glass pane.  This pane is sloped, and the pure water drains downward into a trough, awaiting drinking.

Solar distillation or desalination clearly does not produce a great deal of fresh water quickly, so other more expensive but more productive methods were developed.

Vacuum distillation decreases the pressure in a container of seawater to near that of atmospheric pressure.  This causes the pure water to boil at a lower temperature, allowing it to be separated from the salt (which is very difficult to boil as noted above).  This pure water is again separated and collected.

The most recently developed method is reverse osmosis, where seawater is pumped at very high pressures through a semi-permeable membrane (which only allows water through).  The salt remains.  This method is generally cheaper than vacuum distillation.  The biggest desalination plant in the Western Hemisphere is now being built outside San Diego.

Both vacuum distillation and reverse osmosis use electricity, making them both expensive and polluting.  They also leave an unwanted byproduct of very salty water which must be discarded.  If this brine water is just mixed in with ocean water again, many animals in the area of the brine will die.  Also, the costs of desalination preclude it from being used for any purpose beside drinking and cooking water.  Irrigation would clearly be far too low value a purpose for this water.

So, if desert countries do increasingly come to rely on desalination for drinking water, how can they grow trees and other plants for food production - especially since desalination is expensive?  The answer is - they can use the Groasis Waterboxx.

The Groasis Waterboxx doesn't use salt water at all, but rare rainwater and condensation to grow plants.  Unlike most types of desalination, it doesn't use electricity and doesn't have any moving parts.  A tree or other plant is planted with the Waterboxx, water is poured around the tree, the Waterboxx is filled with water, and the grower's job is done.  The Waterboxx will maintain its water supply from condensation and refill completely with 4 inches of rain.  See a video of how the Waterboxx works below (from Groasis):



The Groasis Waterboxx allows trees and other plants to be planted in deserts and other very dry areas with high survival rates.  88-99% of trees planted in a Sahara planting trial survived using the Waterboxx, versus only 10% that survived without the Waterboxx but with weekly irrigation.

The Waterboxx has been used throughout the world, and Dew Harvest® is now distributing the Waterboxx within the United States.  The Waterboxx allows land owners and gardeners to plant all types of trees and many different garden plants.  We document our success with pear, cherry, oak, and sequoia trees as well as cantaloupe and pumpkins elsewhere on this site (click the respective plant for links).  Be the first to in your area to start growing with the Groasis Waterboxx.  Buy the Waterboxx here.

You can see all our blog posts about planting trees with the Waterboxx here.We would love to hear your comments below - to leave one, please click on "Comments".

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