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Advanced Water Treatment Research--->Environmental Issues

Seawater

The ocean is full of life, and desalination plants that use seawater need to consider interactions with sealife--particularly microscopic phytoplankton.Large numbers of phytoplankton attract large numbers of other hungry creatures, which may also interact with desalination plants.

Higher levels of chlorophyll indicate a high concentration of phytoplankton.Coastal areas (where most seawater desalination plants are) tend to have higher concentrations, and thus higher levels of sea life. NASA monitors chlorophyll levels in the oceans through the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua Satellite. The figure shows chlorophyll levels for May 2011. Light yellow shows the highest concentrations and dark blue the lowest (light grey areas have no data due to cloud cover).See the Earth Observatory web site for more images.


Chlorophylll

Small sealife can enter the desalination plant intake screen (entrainment) and pass through to the treatment facilities. Or sufficiently large organisms are trapped against the intake screen by water suction (impingement). Both fates result in death of the organism. To help prevent entrainment, buried subfloor intakes act as media filtration systems and separate sea life from the intake pumping system. Flow is spread over a larger surface area allowing a much smaller flow velocity. To help avoid impingement, the intake flow velocity must be less than usual currents to allow fish and pelagic marine life to swim or drift away.

WateReuse Research Foundation Desalination Committee White Papers has two excellent reports on intakes:

The Desalting and Water Purification Research Program has funded subfloor intake system research to eliminate the problems of impingement and entrainment (DWPR #66)

Title

Performing Agency

Year

Report #

Initial Evaluation of the Subfloor Water Intake System Structure (SWISS) vs. Conventional Multimedia Pretreatment Techniques

Pacific Research Group

2001

66

Research and Development for Horizontal/Angle Well Technology Municipal Water District of Orange County>(abstract)

Orange County Water District

2008

151

Results of Drilling, Construction, Development, and Testing of Dana Point Ocean Desalination Project Test Slant Well

Orange County Water District

2008

152

Subsurface System Intake Feasibility Assessment

Orange County Water District

2008

153