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Is Desalination the Answer to California’s Looming Water Crisis?

Posted by: Aqua Blog Maven on May 30, 2007 at 9:44 pm

An Aquafornia Exclusive:

In Southern California, much of the water we use here is imported from the San Francisco Bay-Delta area, the Owens Valley, and the Colorado River. Southern California is experiencing its driest year on record, and water resources throughout California and across the Southwest are being impacted by a persistent drought, global warming, and continued population growth. With 20 desalination projects proposed for the California coast, desalination is being considered as an answer to California’s dwindling water supply. Desalination would provide a reliable, drought-proof water supply from a seemingly endless source and would give local control to municipalities who are located far from fresh water sources. But is desalination truly the answer to California’s water shortage?

There are two main processes for desalinating water: thermal evaporation or reverse osmosis. Thermal evaporation uses heat to produce water vapor, which is then condensed into fresh water. Thermal evaporation is the method used most widely in the Middle East, where energy is abundant and fresh water is not. On the other hand, reverse osmosis uses a membrane to separate the salts and other contaminants. Reverse osmosis is mostly used here in the United States. Both of these methods require an enormous amount of energy to treat the water, with energy costs accounting for at least half the cost. Desalinated water is especially vulnerable to escalating costs during times of drought; since a major portion of California’s energy comes from hydropower; in drier periods, power output of hydroelectric plants is reduced and power costs increase, thereby increasing the cost (Cooley, Gleick and Wolff). Recent advances in wind-powered and wave-powered desalination plants have shown promise in some parts of the world, but can only be implemented in areas where the weather conditions are appropriate.

The method of water intake is a major area of concern. Seawater is a habitat that contains an entire ecosystem. Larger fish and aquatic life are killed on the intake screen; the smaller organisms are killed during the processing of the water. These organisms are then disposed of in the ocean, and the decomposition of these organisms can reduce oxygen content and have an adverse impact on the environment near the discharge point. Subsurface intake wells can be an alternative, but limit intake volumes of water and cause salt water intrusion into freshwater aquifers and degradation of the beach environment.

The desalination process can introduce new contaminants at many stages. The intake water may contain biological contaminants, such as viruses, protozoa and bacteria, as well as chemical contaminants from urban and agricultural run-off, which may or may not be removed by the filter. During pre-treatment, the water is treated with chemicals to prevent membrane fouling. As the water goes through the membrane, minerals, such as magnesium and calcium, are removed; this is a health concern because ingestion of low-mineral water can leach vital nutrients from the body. The treated water also tends to be acidic, which leads to corrosion of the distribution system. To minimize these effects, calcium carbonate is added in the post-treatment process. Chlorination may also be required, and careful monitoring and management is necessary.

The by-product of desalination is brine, which contains a higher density and concentration of salt, manganese, lead, iodine, pollutants from urban and agricultural runoff, as well as the aquatic life that was killed in the process. Chemicals used in the process may be discharged with the brine, and corrosion of equipment may cause leaching of heavy metals into the waste stream. The brine is usually discharged into the ocean, and can impact the marine environment at the discharge point. Certain habitats and aquatic life are more at risk than others, and there is a need for more comprehensive analysis and studies.

Desalination may seem like the answer to our needs: a reliable, endless source of water, but the energy required to produce it and the impact on the marine environment present significant challenges to a state concerned with electrical shortages, global warming, and continued degradation of the environment. The energy-intensive desalination process does not produce abundant amounts of water; if all of the 20 desalination facilities proposed were built, their combined capacity would have provided only 6% of California’s water use in the year 2000 (California Coastal Commission, 2004). If the City of Santa Barbara’s desalination plant were operational, it would supply about 15,000 homes with water, and yet consume the same amount of energy as a small steel mill. Research and development has been focusing on improving reverse-osmosis membranes for increased efficiency and reliability; but despite these advances, the cost of desalinated water remains at least twice as expensive as conventional water supplies. Recent advances in renewable energy sources show some promise in areas where the proper weather conditions exist; however, these technologies are still unproven, and it is questionnable as to whether they can be implemented on a large-scale basis that would be able to supply a meaningful amount of water for California.

But perhaps the greatest risk of all would be to the ocean environment. Few studies have performed or any comprehensive analysis done on the effects of brine discharge on the marine environment. Historically, coastal development has been restricted by many factors, one of them being a limited fresh water supply. Desalination would provide a new, abundant water source for coastal communities, thereby encouraging development in fragile areas. The California Coastal Commission noted in its 2004 report that “a desalination facility’s most significant effect could be its potential for inducing growth” (California Coastal Commission, 2004).

For more information on desalination:

“Seawater Desalination and the California Coastal Act”, California Coastal Commission, March, 2004. Visit: http://www.coastal.ca.gov/energy/14a-3-2004-desalination.pdf

“Desalination: With a Grain of Salt – A California Perspective”, The Pacific Insitute, June 2006. Visit: http://www.pacinst.org/reports/desalination/desalination_report.pdf

For more information on wave-powered desalination barges, click here.

For more information on wind-powered desalination, click here.

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May 30, 2007 · Filed Under Articles, Desalination

Comments

One Response to “Is Desalination the Answer to California’s Looming Water Crisis?”

  1. Linda Walsh on February 20th, 2008 6:19 pm

    I hate to sound simplistic, but I think CA just doesn’t have the ‘will’
    to do desalination.

    You claim that we would have to use reverse-osmosis to desalinate here.
    I’m not so sure if that makes sense. Where is water most needed right
    now? So. California. What does SoCal have “alot of”? A: sunshine.
    Why not use sunshine to power the desalination plant. It should be
    feasible for 100% of the energy to be provided from solar — and
    not the low efficiency solar-cell kind.

    Given enough area (would be sparse near the coast, but a large “canal”
    inland far enough to where the land less expensive and it’s generally
    sunny and dry. Yeah — they would be huge aqueducts — but the idea
    would be to also make them *deep* aqueducts — lower than sealevel (we
    don’t want to waste electricity pumping if we don’t need to, but we
    might
    need to use some to pump the extra salt water back out — maybe a mile
    or so off the coast…Possibly could use temperature variations in the
    water to suck the salt water out, minimizing or eliminating need for
    pumps in either direction.

    So how would it work — the water comes in via giant (the romans did
    this ages ago…can’t we?) aqueducts…reaches spot near sea level
    (managing levels for tides might be tricking, but not impossible to
    solve; also need to account for 200-year storm surges (want this to
    last a while). But bring the water into black-painted heating lakes,
    ponds, tubes — not sure what would be best…. The water evaporates.

    A 2nd level of water (ok some pumping via solar-cell) might be needed,
    would be covered by a white roof, but not sealed…so water is shaded,
    but would evaporate. The evaporating water on top would result in
    a cool surface that the warmer water from the black heated bottom
    could condense on and be collected. The concept is simple — just needs
    enough land area to be feasible — and the land that would be best is
    that which is too hot & dry to use for anything else (too bad death
    valley isn’t closer to the coast!).

    For water from the black pipes that doesn’t evap — it will be the
    higher-salt density water. It needs to be run in a pipe out far
    enough till we can get to *deep* water. Deep water is at 4C and is
    the most compact state of water. Put a long enough upward siphon from
    the deep water that can draw in the high saline (but considerably warmer
    and less dense) return flow and it might be possible to create a
    sustained syphoning flow to pull water from the return-canal…. Thus
    neither direction, ideally, would require pumping, and the condensed
    water would build up in a reservoir until it was at a high enough level
    to “flow” downhill to the needed areas in the south.

    Given enough land and sun, this should take little energy to operate.

    It might be best to build it as far south as possible — if big enough,
    might supply water for areas in Mexico as well — where land might be ‘
    cheaper. I.e. Us & Mexico could co-build (mostly US) the facility, and
    Mexico’s payment would be some % of the water produced.

    All *primitive* technology, but could be designed to last for ages (or
    until a bad earthquake takes it apart — perhaps another good reason to
    build it near or in Mexico — don’t know if the fault lines extend there
    far enough.

    I’ve no clue what the size would have to be, but there are already
    solar-powered water distillers for use on a small scale (see
    http://www.epsea.org/stills.html or
    http://www.thefarm.org/charities/i4at/surv/sstill.htm or just search
    google….

    Linda Walsh

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