What Is Desalination?
As the City of Corpus Christi pushes forward with its dangerous proposal to build a major seawater desalination facility on the Inner Harbor of the Corpus Christi Bay, it’s important to understand exactly what desalination is, how it works, and why the Inner Harbor facility poses such a threat to our Bay.
Desalination is the process of removing salts and other impurities from seawater or brackish water to produce fresh, potable water.
The two primary methods of desalination are thermal distillation and reverse osmosis.
Thermal distillation, utilized less frequently than reverse osmosis, involves heating saline water to produce water vapor, which is then condensed into freshwater, leaving salts and impurities behind. There are several types of thermal distillation.
Reverse osmosis, used in nearly 70% of desalination facilities, is membrane-based process that involves forcing pressurized saline water through semi-permeable membranes that allow water molecules to pass while blocking salts and impurities. Key steps in the process include:
Intake: Seawater is drawn into the desalination plant through intake structures.
Pre-Treatment: The incoming seawater undergoes pre-treatment to remove suspended solids, organic matter, and other impurities that could damage or clog the reverse osmosis membranes.
Pumping: After pre-treatment, the filtered seawater is pressurized using high-pressure pumps to overcome the natural osmotic pressure.
Separation: Under high pressure, the seawater is pushed through semi-permeable membranes that allow only water molecules to pass, effectively separating them from dissolved salts, minerals, and other impurities. The result is two streams – desalinated water suitable for consumption or industrial use, and brine, a concentrated solution containing the removed salts and impurities.
Post-Treatment: The desalinated water is treated to ensure it meets drinking water standards and to improve taste and stability. This may include adding minerals like calcium and magnesium, or applying chlorination or other disinfection methods.
Effluent Discharge: At this point the pre-treatment sludge and the remaining brine, which is approximately 58% of the intake water and contains a higher concentration of salts, is mixed and returned to the ocean. The brine is typically discharged through diffusers to promote mixing and dilution.
Many desalination plants around the world have encountered major challenges. These include:
Huntington Beach Plant, in California: Proposed over two decades ago, this $1.4 billion project aimed to provide 50 MGD. However, in 2022, the California Coastal Commission unanimously denied the necessary permit, citing concerns over environmental impacts, marine life disruption, and cost-effectiveness. The decision led to the project’s abandonment.
Tampa Bay Plant, in Florida: Designed to produce 25 million gallons per day, this facility faced numerous issues, including technical malfunctions, contractor bankruptcies, and significant cost overruns. Initially budgeted at $110 million, the final costs exceeded $158 million and the plant struggled to meet its production goals.
Perth Plant, in Australia: This $400 million plant was designed to supply 17% of Perth’s drinking water. While operationally successful, it has faced criticism due to its high energy consumption and environmental concerns related to brine discharge affecting marine ecosystems.
The City of Corpus Christi is currently advancing plans to construct a $757 million reverse osmosis seawater desalination facility in the Inner Harbor of Corpus Christi Bay to support regional industrial growth, with a proposed output of 30 MGD.
A broad coalition of Coastal Bend community groups have strongly opposed the City’s Inner Harbor plan based on the huge risk of discharging millions of gallons per day of salty brine water into our shallow, partially-enclosed Bay.
To learn more about the risks associated with this proposed facility, please read the Current’s “Inner Harbor Desalination 101” regular series.