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Water desalination could be key to combating freshwater scarcity, a vital and indispensable resource, whose lack is already resulting in a serious humanitarian, environmental and economic crisis in many corners of the planet.
However, Sometimes, desalination of seawater can be impractical in economic and energy terms.This requires seeking the most innovative and viable options for each case.
What is seawater desalination?
Seawater desalination (or desalination) consists of to remove salt and other dissolved minerals from seawater so that it is suitable for human consumptionagriculture, livestock farming, or industry.
The process is carried out in specific plants, through the separation of salts from a brackish solutionThat is, a mixture of water with a high salt concentration.
Although it is completely safe, seawater desalination is not always efficient.
In fact, it is estimated that, For every liter of water that is processed, barely half is ready for human consumption. while the remainder must be returned to the sea due to its high concentration of salts and minerals
In any case, if the current drought situation is not reversed, the different methods of seawater desalination They could become the only alternative to supply drinking water to thousands of people around the world.
This is the process for desalinating seawater and making it drinkable.
Conventional desalination processes They separate the water coming from the sea into two parts:
- Liquid with a low concentration of dissolved salts.
- Concentrated brine (process waste).
Regarding methods for desalinating seawater, They can be classified into two main categories:
Thermal or pressure evaporation methods
They use pressure and heat to evaporate the water and thus separate the liquid from the salt. The most common are:
- Multi-stage flash distillation
Multi-stage desalination consists of placing seawater in several successive chambers or stages, with decreasing pressures and temperatures, for evaporation and condensation.
Very similar is the "flash evaporation", which consists of introducing seawater, in droplets, into a low-pressure chamber.
In both cases, the droplets turn into water vapor which, upon condensation, loses salinity.
The process can be repeated as many times as necessary until the optimal water desalination level is achieved.
- Multi-effect distillation
In the process of seawater desalination by multi-effect distillation, andn Instead of using pressure to evaporate the water, heat is used.
That is to say, The water boils until it turns into steam, which then condenses.
The results are similar to multi-effect evaporation, although requires a greater quantity and intensity of energy.
- Vapor compression
The excess heat from power plants or refineries is used to evaporate and condense seawater, purifying it.
It is one of the methods for desalinating seawater more efficient.
Membrane-based separation methods
They use mechanical pressure, electrical potential, or other types of barriers to separate the salt from the water. The most common are:
- Inverse osmosis
Reverse osmosis is used both to desalinate seawater and to transform any other salty substance into a purified one.
It consists of separating water from salt by applying pressure to the liquid with semipermeable membranes. that allow the isolation of salts and other contaminants.
The pressure exerted will depend on the amount of solids and the degree of desalination desired.
- Electrodialysis
Applied to seawater purification, electrodialysis It uses electric current to move the salt ions present in the water and, thanks to some membranes, separate the fresh water.
This method is especially efficient for desalinating water with low salinity.
How does a seawater desalination plant work?
Many desalination plants use reverse osmosis.
They collect seawater directly from coastal towers or wells. to then move it to their facilities.
There begins the water desalination and purification process, which we could summarize in the following steps:
- Water enters a "Pre-treatment" zone where suspended solids, microorganisms or bacteria are removed.
- Then, go through sand filters and coagulantsand for a second stage of "microfiltration" with activated carbon (or other similar products).
- Already in the heart of the desalination plant, the following takes place: reverse osmosis process.
- Subsequently, a The pressure pump forces water through different semipermeable membranesso that it is completely free of saline residue.
- It starts on post-treatment of water for its adaptation to human consumption, Remineralization is necessary to ensure it has the optimal components and pH (according to the WHO, the ideal pH of drinking water should be between 6.5 and 8.5).
- The excess brine is removed and is returned to the sea diluted to prevent damage to the marine ecosystem where it is returned
Benefits of seawater purification and long-term challenges
Purifying seawater has many advantages and could become a viable solution to the growing demand for fresh water on the planet.
Some of them are:
- Seawater desalination plants have potential to convert large quantities of seawater into water suitable for human, agricultural and industrial consumption., something fundamental in coastal and arid areas.
- These facilities They facilitate water independence, since communities can reduce their use of unstable or insufficient freshwater sources.
- Advanced seawater desalination processes They are safe, and guarantee quality water. without contaminants or salts.
Despite these important benefits, seawater desalination also presents significant challenges, among them:
- El high energy consumption of the desalination plants.
- La brine management and its impact on marine fauna.
- El use of chemical productss in membrane pretreatment and cleaning.
- El equipment maintenance, exposed to high corrosion due to high salinity.
In SITRA We work in all stages of the complete water cycle in industry, which includes the design and construction of wastewater treatment and desalination plants, or the operation and maintenance of existing facilities.
We prioritize efficiency, recycling, waste valorization, and digitalization in every project.
