Water is essential for the maintenance of life across the planet. In an adult individual, for example, water makes up about 60% of the organism . Therefore, this resource is essential for the hydration of humans and also animals and plants. In addition, water acts directly in the transport of substances, regulates body temperature and is essential for the body’s chemical reactions.
Among several other functions of water, we can mention the maintenance of the Earth’s atmosphere, which provides the ideal climate for the survival of life on the planet, as well as for agriculture and the economy.
However, despite the fact that 71% of the Earth’s surface is covered by water, only 2.5% of this available amount is fresh . Furthermore, the mechanisms for the renewal of this resource are few, slow and limited, which makes drinking water a finite resource. Thus, to avoid depletion, it is necessary to implement measures to avoid waste.
In this sense, with the concern of scarcity in mind, techniques began to be developed to make salt water potable, such as the desalination of sea water. In this article, we’ll cover what this process is, what the steps are, how it works in practice, and what the costs are involved. Check out!
What is the seawater desalination process?
Salt water, or sea water, represents about 97% of the entire planet’s water . However, it is unfit for consumption. First, it contains high levels of sodium chloride, the same salt used in food preparation.
When there is an excess of this substance in the body, cells begin to lose water in a process called osmosis, causing dehydration. This condition is quite dangerous for health, since water is essential in various chemical reactions and body functions. In addition, seawater is rich in some salts that can irritate the lining of the gastrointestinal tract.
However, experts believe that this highly available resource is being wasted. That’s because there are ways to remove excess sodium chloride and other salts from sea water, as well as microorganisms and other components that are harmful to health, making it ideal for consumption.
What are the steps in this process?
There are basically three sensitive parts in the desalination process: the capture, the treatment itself and the disposal of the tailings. Better understand each step below.
fundraising
The first phase of the desalination process is the capture of sea water. Therefore, it is possible to build Pumping Stations close to the beaches, as well as capture it through channels, wells or infiltration galleries.
Treatment
Within the treatment stage, it is possible to use various processes, such as filtration, flotation, ultrafiltration, evaporation/distillation, reverse osmosis and remineralization, as well as combining the techniques to achieve more efficiency.
The best known processes are the use of ultrafiltration membranes in reverse osmosis, as well as evaporation/distillation.
Ultrafiltration and Reverse Osmosis
In this case, the passage of sea water occurs through membranes with selective permeability. During desalination using the reverse osmosis technique, the passage of water through the membrane water purification companies occurs because the external pressure is greater than the existing osmotic pressure, which makes the liquid move from the side with the highest concentration of salts to the side with the least concentration of salts . The goal is to reverse the natural process of osmosis.
The membrane used promotes ultrafiltration, as it is made of semi-permeable and synthetic material, with a thickness of less than 1 micron. When water moves through it, impurities are retained and, thus, the separation of salts, minerals and other contaminants that made the water unsuitable for consumption occurs.
Evaporation
Thermal distillation, or evaporation, mimics the natural cycle of rain to promote desalination. By means of energy, which can be fossil or solar, sea water is heated and thus changes from a liquid to a gaseous state.
The solid particles will be retained in the reservoir, while the evaporated water, already without mineral salts, will be captured by a system that will cool it and make it return to a liquid state.
tailings disposal
Wastewater from desalination has a high concentration of salts, minerals and other compounds, including waste toxic to marine life. Furthermore, in some cases, such as in the evaporation process, the water resulting from the treatment is at a different temperature from that found in the sea, which can cause negative impacts.
Therefore, it is necessary to distribute the tailings without impacting marine life and the soil, as the tailings are often returned to them and to water courses. For that, there are several techniques, such as evaporation basins or ponds, brine concentration and crystallization, reduction of the waste volume by aquatic plants in ponds and percolation basins and irrigation of halophyte plants, that is, plants that accumulate large amounts of salts inside.
Is there feasibility to apply desalination of sea water?
Desalination of sea water is very common in desert regions, such as the Middle East, or with limited availability of drinking water , such as in Africa. However, the use of this technique is not restricted to just these places, being widely used around the globe, mainly in Spain and the United States.
In Brazil, this idea has been applied since 2004 with national technology. The result is 575 desalination systems in operation: 234 in Ceará; 44 in Paraíba; 29 in Sergipe; 10 in Piauí; 68 in Rio Grande do Norte; 45 in Alagoas; and 145 in Bahia. In addition, we have 147 stations under construction. Other states, such as Pernambuco, Minas Gerais and Maranhão, are already in the initial stage of diagnosis. In total, we have 924 systems contracted in the country, in the most diverse phases of the process.
A negative point is that seawater desalination plants, especially large ones, demand a high consumption of electricity. However, as Brazil has a high incidence of sunlight, it is possible to use this energy to move the plants. Another topic that deserves attention is the need to have an adequate management plan for the waste involved in the process.
As seen, seawater desalination is a process that is here to stay, and should be understood as one of the necessary alternatives for the management of water resources, continuity of industrial development and population growth.
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