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Desalination in California
A recent Californian report (1) suggested that “the question is not whether, but rather how, where, when and by whom… will desalination projects be designed, built and operated”. In 2004 the state had 12 desalination plants in operation and a further 24 at different stages in the planning process. The current plants are small-scale with a total production of 11.4 million litres per day, but if all the proposed desalination plants became operational, production would rise to 908 million litres/day.
Poseidon Resources have been operating Carlsbad Desalination Project in San Diego County as a pilot plant since 2003, producing c.150 000 litres/day of freshwater. The plant, which sits on the same site as Encina Power Station, takes used cooling water from the power station, filtering it and passing it under pressure through reverse osmosis membranes. Currently San Diego County imports up to 95% of its water so the decision of the Water Authority to support the desalination plant is in an attempt to diversify the water supply and thereby provide greater security of supply.
Proposals have been submitted to turn the site into a full-scale 300 million litres/day plant. With a draft environmental impact report complete, construction is due to start in 2006 should the final go-ahead be given from the necessary authorities. 300 million litres/day would deliver enough drinking water for around 500 000 residents which equates to 15% of the County’s supply (2).
Highly saline wastewater from the desalination process is mixed with used cooling water from the power station prior to discharge to the sea in order to reduce salinity. Concerns have still been raised however, because the salinity of seawater in the vicinity of the outfall pipe is reported to be between 1 and 8% greater than in surrounding seawater. Poseidon Resources point out that blended water from the pilot plant has been tested and declared 'environmentally safe' even under worst-case discharge conditions (3).
Marine biologists have taken species recorded in the area and placed them in an aquarium tank containing water of a salinity approximate to the range expected with the full-scale desalination plant. Preliminary results show that the organisms are able to cope well with the change in water conditions. Poseidon Resources also point out that salinity concentrations soon defuse to background levels when the outflow water mixes with surrounding seawater (3).
References
(1) California Coastal Commission (2004) Seawater Desalination and the Californian Coastal Act. Pg5
(2) San Diego County Water Authority. Press release: Water Authority and city of Carlsbad release agreement on seawater desalination project (2005) http://www.sdcwa.org/news/041905carlsbaddesalagree.phtml
(3) Poseidon Resources – The Carlsbad Desalination Project. Environmetal Responsibility (2005) http://www.carlsbaddesal.com/respons.htm
(4) San Diego County Water Authority. Seawater desalination (2005) http://www.sdcwa.org/manage/sources-desalination.phtml
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