Sea water desalination methods
Reasons for resorting to methods of desalination of sea water
According to the World Health Organization, around 785 million people globally lack a clean source of drinking water close to where they live, needing to walk half an hour to reach it, and this problem is getting worse as the global climate crisis continues.
Given that saline water constitutes about 97 percent of the water on the planet, scientists view sea water as a large untapped resource for life-giving drinking water. world level.
Reverse Osmosis
Osmosis is the net movement of water molecules across a semipermeable membrane from an area of high water density (example: fresh water) to a region of low water density (example: salty sea water) without the need for energy consumption, because the semipermeable membrane allows the permeability of water (solvent). ) and does not allow the solutes to pass through, which leads to a pressure gradient across the membrane.
Reverse osmosis requires the use of energy and pressure to push the water solution through a permeable membrane that prevents large dissolved particles, such as salt, from passing through it.
The downsides of this process are:
The membranes in them during their use are exposed to the accumulation of a lot of bacteria on them, which may lead to clogging, although they have become more effective over time, and these membranes are damaged when chlorine is used in them to treat bacteria.
Poor water quality.
The need for a pretreatment of salt water.
Consuming a large amount of energy.
electrical separation
Through this technology, sea water is desalinated by using electric current to separate water from salt, so that the electric current isolates sodium and chloride ions from sea water through a selective permeable membrane. They can be thrown out. One of the downsides of this process is that it is considered a suitable process for desalinating water in which the salt concentration is primary, but it also consumes a lot of energy to desalinate sea water.
multistage flash
The multi-stage rapid distillation process is applied based on the scientific fact that determines that the boiling point of liquids is directly proportional to the pressure on them. The lower the pressure on the liquid, the lower its boiling point. This is how sea water passes after being heated to successive chambers of low pressure, and the water turns into fresh water vapor that is condensed on cold surfaces, collected and treated in potable quantities. This method is used in desalination plants with large production capacity (30,000 cubic meters, or about 8 million gallons of water per day). The remaining salt concentrate is known as “brine”, and no chemicals or softening agents are usually added to the water.
Multi-effect distillation
The multi-effect distillation process is similar to the previous process (multi-stage flash distillation), in which the multi-effect distillation takes advantage of the vapors rising from boiling sea water in the first evaporator to condense in the second evaporator. The same process is repeated in the third evaporator, by spraying the feed water on the group of tubes above each evaporator. Thus, each evaporator in that series is called the effect, whereby the water vapor condenses to turn into fresh water inside the tube, and then it is pumped into special channels.
Forward Osmosis
Forward osmosis uses the naturally occurring osmotic process, namely the movement of water molecules across a semipermeable membrane from an area of high water density (example: fresh water) to an area of low water density (example: seawater). This process requires about half the cost of the reverse osmosis process because it consumes less energy to complete the process. However, since it is still a new technology for large-scale desalination, this process needs funding and research to explore its implementation possibilities, aspects that need improvement, and improvements required to reduce energy costs.
PMFs
This new innovation developed by scientists in Australia is the most successful to date, with researchers using MOFs (or MOFs) combined with sunlight to purify water in just half an hour, using a more efficient process than existing technologies.
One of the advantages of these compounds is that they are cheap, stable, reusable and produce water that meets WHO standards for desalination. About 139.5 liters (approximately 37 gallons) of clean water can be produced per day from a kilogram of PFs based on early testing.
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