Saturday, May 30, 2015

The Quest to Quench the World’s Thirst for Water

The desalination plant in Carlsbad will use the reverse osmosis process to produce fresh water. (Credit: Dima/flickr) Click to Enlarge.
As climate change makes rainfall less predictable and droughts more common, a growing number of countries are turning to desalination.  The term is used to refer to removing salt from both seawater and subterranean “brackish” water, as well as the treatment of waste water (aka sewerage) to make it drinkable.

Some environmentalists have long opposed desalination because of the energy the process demands, as well as other considerations such as the impact of sucking in large quantities of seawater from the ocean.

But technological advances in recent years have altered the equation.  The most common form of desalination is reverse osmosis; it involves forcing water through cartridges that contain thin-film composite polyamide membranes, which trap salt and other impurities but allow the fresh water through.

Randy Truby, comptroller of the International Desalination Association, says that advances in manufacturing processes have allowed 450 square feet of membrane to be crammed into each cartridge, compared with 300 square feet when they first came on the market.  But treating seawater still requires pressure of about 1,160 psi, 40 times more than car tires.  That is why treating seawater is more energy-intensive than brackish or waste water, which require less force.

The location of a seawater desalination plant also makes a difference, Truby adds:  while the salt content of water off the coast of California is about 34,000 parts per million, the figure in the Middle East is more like 40,000.

Read more at The Quest to Quench the World’s Thirst for Water

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