The cells of the body carry out the process of osmosis or what is called the osmosis process when water passes through its outer membrane, so the cell tries to equalize the high salt concentration inside it with the low salt concentration outside it, and therefore this process has been used in the process of reverse osmosis (in English: Reverse osmosis), which They occur when salt water is placed on one side of a semi-permeable membrane, and the water molecules are moved by pressure through the filter membrane, so that large molecules, including salt particles, that are behind the membrane do not pass through it, as for salty water in the seas or oceans, there is a need for a large amount of pressure that is required to transfer water through the filtering membrane, as each pore in it is the size of a small part of the size of a human hair, and this means that a series of pumps must be operated, so that they all pressurize the water.
The process of forward osmosis (in English: Forward Osmosis) uses the natural osmosis process; In which the material moves from an area of low concentration to an area of high concentration, where the process consumes less energy than that used for the reverse osmosis process, which leads to reducing the cost in half compared to the cost of reverse osmosis, instead of exerting force on the solution through a pressure gradient This process allows the solution to move naturally, so when desalinating water, the sea solution moves through a semi-permeable membrane to a highly concentrated solution of ammonia salts, and the sea salts remain on the other side of the membrane, then the solution is heated to evaporate the ammonia salts from it, and the resulting salt is usable, but this technology is fairly new for its application to desalination on a large scale, and therefore it needs funding and research to identify points that can be improved, and that reduce energy costs.
Electrodialysis uses a membrane in its operations, as in reverse osmosis, to send electric charges through the solution to pull metal ions toward a positive plate on one side, and to pull other ions, such as salt, to a negative plate on the other. others, then the charges are reversed periodically; To avoid contamination of the membrane significantly, and then the ions on each of the plates can be removed, which results in pure water, and new chlorine-resistant membranes have been made that remove harmful ions, and despite their effectiveness in water desalination, they are expensive, in addition to the presence of costs energy.
The solar humidification process can be used in places where salty water is available and intense sunlight, where the sun's heat evaporates the salty water that is under a transparent cover, then the steam condenses at the bottom of the cover, and flows into a basin to collect pure water, but this process requires large areas of land and energy in order to pump water, and it should be noted that there is another thermal process that takes advantage of the fact that if salt water is frozen, the ice crystals do not contain salt, but in practice the quantities of water remain Unwanted saline is confined between the crystals, in addition to the amount of fresh water needed to get rid of the salty water is similar to the amount of fresh water resulting from the dissolution of the crystals.
Multistage rapid distillation
The distillation process removes salt and other types of pollutants from the water, and the multistage flash distillation process takes place by reheating the water resulting from the heating several times, and the pressure is reduced each time it is reheated. The stages are built alongside the power plants in order to take advantage of the heat dissipated from these stations, so these distillation plants require a much lower amount of energy compared to the reverse osmosis plants for distillation, but the main problem of multi-stage rapid distillation is that it requires a larger amount of salt water from reverse osmosis, and maintenance costs are high.
The Multiple-Effect Distillation process is a simple process similar to the rapid multi-stage distillation process, in which the salt water solution is heated, which results in pure water flowing to the next chamber, and the thermal energy carried by the resulting water is used to boil again , which leads to the production of more steam, but it is better to use this method for desalination of water on a smaller scale, because its costs are very high for large facilities.