Do you ever think about things and forget about them because of how much time and effort it would take to explore, validate, understand, or dispel them? I do. It happens a lot actually.
One of these recent intellectual pangs included desalination. This time though, I committed myself to understanding it rather then letting it go because of how inconvenient it would be to independently learn something new.
What follows is a piece I put together based on my research. Disclaimer: I am not a scientist, environmentalist, journalist, or academic. This is simply an educational exercise from the perspective of a layman.
Interestingly, writing this made me realize two things. First, how easy it is to write about what we enjoy. This highlights the larger and more conventional theme of safety and comfort. We rarely push ourselves to learn, study, and contribute to topics that are outside our scope of knowledge because they are difficult and challenging (aka not comfortable or safe). Secondly, we don’t question things or people as much as we should. It takes a healthy amount of time and effort to study and learn something we’re not familiar with. Many people simply don’t bother (myself included). This is intellectually dangerous as it keeps us in a familiar and tiny bubble, without the ammunition to question and validate what we hear from friends, family, religious affiliations, politicians, and the media.
So apologies in advance if this piece comes off as sloppy, uninformed, slanted, or boring. What I’m not apologetic about is in publishing it, since I hope it will lead to future discourse or inspiration for others to learn something new. Enjoy!
Desalination in California?
Living in California it is commonplace to hear about water conservation efforts to combat a historic and longstanding drought. California’s coastline hugs the Pacific Ocean, which happens to be the world’s largest ocean. This equates to 68 million square miles or 187 quintillion gallons of water, enough to fit all of the world’s continents in its basin or fill 283 trillion Olympic size pools.
Couldn’t this large mass of water be utilized to aid or alleviate modern droughts, especially among coastline states? Before tackling this seemingly obvious question/solution it is necessary to understand what saltwater is and what are the methods and byproducts of salt extraction.
Saltwater & Salinity
A fundamental property of saltwater is salinity. This refers to a percentage of distilled salt found in a given liter of water and is commonly referred to as PPM (parts per million). PPM is a metric unit and is expressed in increments of thousands. For example, the Pacific Ocean ranges from 32,000 to 37,000 PPM. This means that its salinity is between 3.2% – 3.7%.
U.S. health specialists and government bodies state that ideal drinking water (also known as fresh water) should be below 50 PPM or less than 0.005%. Water for agriculture and irrigation should not exceed 500 PPM or 0.05%.
A major side effect of saltwater consumption is dehydration, which can ultimately lead to organ failure and death. Use of saltwater in agriculture is discouraged as most crops do not grow well on soils that contain salts. Water absorption by plant roots is severely impaired by the presence of concentrated salts.
A Tale of Two Processes
Two of the most common methods of desalination are Multi-stage Flash Distillation and Reverse Osmosis. Multi-staged Flash Distillation is a process of heating water through various pressurized chambers to create steam. The end result of this “flashing” or steaming is a multi-tiered water evaporation process that leaves salt behind. Reverse Osmosis involves using high pressure pumps to pass saltwater through various filtration membranes. The pressurized water moving through these various “filters” results in a separation of salt and water.
While these are simple explanations of the two most common forms of desalinization, the actual process is much more complicated. These complex processes are also costly and resource burden.
Desalination plants are very expensive to build and operate. The Carlsbad desalination plant which opened in December 2015 cost $1billion. As the nation’s largest desalination plant, a series of setbacks and plan upgrades contributed to the hefty price tag. A plant designated to serve the Bay Area is currently being planned and includes a cost of $150 million. Operating costs for such large scale plants vary by output capacity, but can easily exceed amounts of $5 million annually. These costs are associated with the large amounts of energy required from fossil fuels and electricity to produce fresh water. Byproducts of this high energy output include greenhouse gas emissions, although modern plants are increasingly turning to wind, solar, and wave technologies as alternative power sources.
Impacts on Environment
Desalination plants extract water directly from the ocean via open water intakes. Fish and other marine wildlife are killed by these intake screens. Smaller organisms, such as plankton and fish eggs, which are able to pass through the intake screens are killed during the desalination process. The net impact on the larger ecosystem is still unknown, and further research is needed to understand immediate and long-term side effects.
Once seawater has been treated, it produces brine as a byproduct. Brine is an especially saline substance. It is twice as saline as seawater, since it contains concentrated amounts of salt left behind from the desalination process.
Brine is disposed of in the ocean and because it is much denser than seawater it tends to sink and spread across the ocean floor. With little to no wave movement at those depths it sits and remains there. This highly saline byproduct can be toxic to marine life if not treated. Many plants employ diffusion methods when discharging of brine into the ocean. These include mixing it with effluent from a wastewater treatment plant or cooling water from a power plant. Another method involves the use of multi-port diffusers placed on the pipes which carry brine out into the ocean. This is meant to disperse brine and promote even mixing as opposed to releasing large concentrated amounts all at once. More research is needed on these efforts as well as alternative disposal methods to gain a better understanding of net impacts on marine wildlife.
Conclusion
The vast size of the Pacific Ocean posits the simple question of using it as a resource to combat droughts throughout California. However, the rationale for why this is or isn’t a viable option is more complicated than that. Large financial and energy resources are required to build and operate these plants. Environmental impacts must also be taken into consideration, as current methods of desalination present threats to marine wildlife and the ozone layer.
Future considerations in evaluating the feasibility and benefit of proposing, building, and maintaining a desalination plant should include return on investment, geo/environmental sustainability, and freshwater sourcing alternatives.
Currently, there are only 3 desalination plants in California. Two small scale plants in Sand City and Catalina Island and the large scale facility in Carlsbad. The scarcity of these plants alludes to the difficulty in simply taking water from the ocean and converting it to clean drinking or irrigating water.
Resources and Links:
Introduction to Desalination Technologies
Desalination Plants Aren’t a Good Solution for California Drought
The Impacts of Relying on Desalination for Water
Key Issues in Seawater Desalination in California: Marine Impacts
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