Desalination: what it is and types

Desalination is understood to be the process of obtaining fresh drinking water from sea water or brackish water , which is that which 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 is a process that produces numerous mineral residues and polluting substances, as well as being quite demanding in its consumption of electricity. For this reason, work continues every day to find ways to optimize salinization processes and make them more efficient and sustainable.

To better understand this topic, we recommend you read these other articles and watch this AgroCorrn video about:

• What is the water cycle .
• Why the sea is salty .
• Why the water of the rivers is sweet .

There are 5 systems to achieve large-scale water desalination . They are as follows:

Inverse osmosis

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 it requires, and that it is necessary to obtain a volume of salt water of 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.

Distillation

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.

Freezing

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.

The most efficient method currently consists of using a refrigerant that, when expanding, freezes the seawater and allows us to collect the clean ice crystals.

Flash evaporation

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.

By electrodialysis

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 electric current, they alternately trap the NA + or Cl- ions, the components of the salt, thus obtaining fresh water.

If you’re wondering how a desalination plant works , take note that reverse osmosis desalination plants follow this process.

1. They begin their process by collecting seawater from underwater towers or coastal wells.
2. This water is taken to the pre-treatment zone, where suspended solids, bacteria and microorganisms are separated from it.
3. It is then filtered using sand filters and coagulants, to pass to a microfiltration stage with cartridge filters with activated carbon or other similar products.
4. From here it goes to the heart of the desalination plant, where the reverse osmosis process takes place.
5. The pressure pump forces the water to pass through 7 semi-permeable membranes, which let out only the water, already free of salts.
6. A post-treatment process is necessary, in which the water is remineralized so that it has the necessary components and pH for human consumption.
7. The excess brine is removed from the reverse osmosis racks to be returned to the sea.

If you want to read more articles similar to Desalination: what it is and types , we recommend that you enter our category of Other environment .