Obtaining drinking water is an increasingly serious and key problem in the future of human development. We need a large amount of water both for our consumption and for irrigation. The surface of our planet is covered by 70% of water, but less than 1% of this is suitable for human consumption. That is why it is so important to be able to convert salt water from the oceans into drinking water, a process that desalination plants take care of. If you want to learn more about seawater desalination methods, join us in this Green Ecologist article in which we talk about what is desalination and its types.
Desalination is understood as the process of obtain fresh drinking water from sea water or brackish water, which is the one that has a salt content of between 0.5 and 30 grams per liter.
This process is carried out in desalination plants of different types. It is not a novel concept, since this type of plant has existed for a long time, but desalination It is a process that produces numerous mineral residues and polluting substances, in addition to being quite demanding in its electricity consumption. For this reason, work continues every day to find ways to optimize salinization processes and make them more efficient and sustainable.
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exist 5 systems to achieve water desalination on a large scale. They are as follows:
This is the most widespread of all current desalination systems, and also the most advanced. 60% of today's desalination is done by reverse osmosis.
Natural osmosis consists in that, if we have two masses of solution with the same solvent and separated by a semi-permeable membrane, the solvent will go through osmotic pressure from the part with the lowest concentration to the part with the highest, until the concentration of both is equal .
In reverse osmosis what we do is apply pressure to force the water to pass through this semi-permeable membrane, which allows the passage of the solvent, but not the solute, thus obtaining water free from the mineral salts dissolved in seawater.
The drawbacks of this system are the amount of energy that it requires, and that it is necessary to obtain a volume of salty water up to three times that which we are going to obtain desalinated. The use of graphene sheets to replace the current membranes is currently being investigated, and which theoretically would give much better performance.
It consists of applying heat to the water to evaporate it and re-condense it throughout different phases, which will give rise to desalinated water. Furthermore, in this system it is possible to use the heat obtained in the condensation to heat new quantities of water to be distilled.
This process seeks to freeze the water to create pure ice crystals, which we can later convert into fresh water. It is a more effective method than distillation, but currently at a disadvantage compared to reverse osmosis.
Currently the most efficient method is to use a refrigerant that, when expanding, freezes the seawater and allows us to collect the clean ice crystals.
This process, also called Flash Evaporation or MVF, consists of introducing the water in the form of drops of small thickness into a chamber at low pressure, below saturation. This change causes part of the droplets to evaporate immediately, and when they are condensed they give rise to desalinated water.
The excess water passes to a next chamber, at an even lower pressure, so that the process occurs again. Some plants can have up to 24+ flash desalination stages.
Permeable membranes are placed a few millimeters apart, with electrodes at the ends. As the membranes allow the selective passage of ions when there is a continuous electrical current, they alternately trap the NA + or Cl- ions, the components of the salt, thus obtaining fresh water.
If you wonder how a desalination plant works, take note that the reverse osmosis desalination plants they follow this process.
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