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San Diego State University

Common Experience Water

Desalination

Problem:

California has limited water resources. Drinking water is no longer in such abundance that it can be carelessly diverted from precious resources such as the Colorado River or the Bay Delta (at the convergence of the Sacramento and San Joaquin rivers).

 

Solution:

Coastal provinces can divert water from the ocean and turn it into drinkable water through the filtration process of desalination.

 

What is desalination?

Desalination refers to the process by which salt and other minerals are removed from saline water by filtration. Saltwater is desalinated to produce freshwater that allows for human consumption or irrigation.

 

How does desalination work?

There are several processes by which water is desalinated including vacuum distillation—essentially the boiling of water at less than atmospheric pressure and thus a much lower temperature than normal. The most common method of desalination is by a process known as reverse osmosis – involving the use semipermeable membranes and pressure to separate salts from water. See Figure 1. 

 

Figure 1

desalination.png

 

Problems with desalination…

 

Intake

Ocean water intakes only work best if significantly reducing the marine life. Beach wells have been used to eliminate this concern, but they require more energy and higher costs, while limiting output.

 

Output

The process of desalination produces large amounts of concentrate, which may contain residues of pretreatment and cleaning chemicals, their reaction byproducts, and heavy metals due to corrosion. Disposal of this waste involves dilution of the concentrate through another stream of water entering the ocean.

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Desalination in San Diego County

 

Poseidon Water Resources

 

poseidon_water_resource.png 

 

Alternatives to desalination [Wikipedia]

 

Increased water conservation and efficiency remain the most cost-effective priorities in areas of the world where there is a large potential to improve the efficiency of water use practices. Wastewater reclamation for irrigation and industrial use provides multiple benefits over desalination. Urban runoff and storm water capture also provide benefits in treating, restoring and recharging groundwater.

 

A proposed alternative to desalination in the American Southwest is the commercial importation of bulk water from water-rich areas either by very large crude carriers converted to water carriers, or via pipelines. The idea is politically unpopular in Canada, where governments imposed trade barriers to bulk water exports as a result of a claim filed in 1999 under Chapter 11 of the North American Free Trade Agreement (NAFTA) by Sun Belt Water Inc., a company established in 1990 in Santa Barbara, California, to address pressing local needs due to a severe drought in that area.

 

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