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How a Desal Plant Works
about desalination > how a desal plant works

There are three streams of water associated with a desalination plant:

• Feed water – water from the ocean or saltwater aquifer that is used to make drinking water
• Product water – the high-quality drinking water resulting from the desalination process
• Concentrate water – nearly twice-as-salty seawater leftover from the desalination process that is returned to the environment

Feed water can be obtained through a number of intake options. For the Coquina Coast Project, the top-ranked intake options for a land-based facility include a screened intake with a pipeline, an off-shore infiltration gallery and radial collector wells.  

Feed water goes through a pretreatment process, which cleans the water prior to the desalting process. RO membranes have a microscopic pore size and can clog easily, so seawater must be treated before the RO process to remove larger particles and suspended solids to ensure a water quality suitable for optimum membrane treatment. A properly designed pretreatment process will reduce membrane fouling, reduce damage risk and protect membrane life expectancy.

The recommended desalting process for the Coquina Coast Project is reverse osmosis, or RO. The pretreated feed water will be pumped at very high pressures, up to 1,000 pounds per square inch, through spiral wound RO membranes, which will filter out salts and other minerals.

The product water will then move on to post-treatment for pH stabilization and disinfection.

The concentrate water will be returned to the environment. Concentrate return must be done with care to protect the environment.  For the Coquina Coast project, the project team will examine each discharge concentrate option and conduct computer models to help design the best method for mixing and dispersing the concentrated seawater. The preferred concentrate discharge options to be evaluated include a subsurface dispersion field, a pipeline with dispersion field and deep well injection.