Judging from the current exploration results of human beings, the earth is the unique "blue star" in the universe. The reason why is blue is because the surface of the earth is covered by sea water and the area covered by sea water has reached more than 70%.
The earth has about 13.22 billion tons of seawater
Directly speaking, with such a large ocean area, we should not be short of water. has no device to "filter seawater" in the human body, so no matter how much seawater is, we are "hard to swallow" .
However, the emergence and development of "seawater desalination" technology has brought hope to mankind. Moreover, in years of research and exploration, new discoveries have been made in "sea water desalination", and is said to improve efficiency by 40%. So does this mean that humans no longer have to worry about freshwater being exhausted?
We will have 13.22 billion tons of fresh water?
The earth has a lot of water but cannot "drink"
We often say that the earth's water resources is very rich, but its implementation is far from what we think. Previously, the research team of United States Geological Survey and Woods Hall Marine Research Institute coordinated the earth's water resources, and pointed out that if these waters are "gathered" into a sphere, then their diameter is only about 1,385 kilometers, which is about the same straight line distance from Chongqing to Shanghai.
is just a drop of "small water droplets"
You should know that , the "water ball" contains all the water on the earth, and even the water in the living organism is included in . However, these waters are still not worth mentioning compared to the size of the earth, not to mention that most of the water in this water ball is that cannot be used for people to drink .
Researchers pointed out that if the "far water" in it cannot be relieved, such as the sea water and salt water lakes, which cannot relieve near thirst, leaving only fresh water (about 2.5% of the total water resources on the earth), then the water ball will become more "mini", and its diameter will be reduced to 160 kilometers, which is only equivalent to a straight-line distance from Shanghai to Hangzhou.
Distribution diagram of earth's water resources
From this we can see that there is indeed a lot of water on the earth, but there is very little water that can be used for drinking. Moreover, currently, more than 68% of the freshwater on the earth are glaciers and ice sheets, and the remaining 30% are groundwater. For example, lakes, surface runoff, etc. can only account for about 1.3% of the total freshwater resources on the earth.
With this understanding, we can see the melting conditions of glaciers in the north and south poles over the years. We can probably think of what kind of terrible crisis our freshwater resources are facing.
Schematic diagram of freshwater resources
It is no exaggeration to say that water shortage has long become a problem of global , and under the trend of increasing population on the earth, the supply and demand contradiction of freshwater resources will be more prominent.
According to United Nations estimates, about 4 billion people around the world are facing resource water shortages for at least one month a year. By 2050, the freshwater supply in 570 cities around the world will decrease by 10%, and 685 million people will be affected by water shortages.
Schematic diagram of changes in per capita freshwater supply in Gulf countries
Therefore, in order to solve the problem of shortage of freshwater resources, people have focused their attention on seawater, and have used seawater desalination as a means to increase water resources open source . Previously, the seawater desalination industry had developed very well with the help of all aspects, and now it has made new discoveries.
New discovery of "sea water desalination"
Let's first learn about sea water desalination technology has developed so far.
First of all, let’s talk about chemical methods. There are only two chemical methods. is hydrate ion exchange method . Next, let’s look at the physical methods. Physical methods can be divided into three categories, is thermal method, solvent extraction method, and membrane method .
Low temperature multi-effect seawater desalination process diagram
It is worth mentioning that some of the three major categories of physical methods can be further divided, such as the thermal method can be divided into multi-stage flash , multi-effect distillation, steam distillation, freezing method, and humidity-enhancing and dehumidification, while the membrane method can be specifically divided into reverse osmosis and electrodialysis.
Currently, the main large-scale references in the industry are multi-stage flash evaporation, multi-effect distillation and reverse osmosis . According to the data, as of 2011, there were more than 16,000 seawater desalination plants around the world, with a total installed capacity of 7.48×10^7m3/d. Among them, the installed capacity of reverse osmosis method accounted for 63% . It is not difficult to see that in the field of seawater desalination, the membrane method has a very high status.
reverse osmosis processing equipment
The so-called reverse osmosis method is also called overfiltering method. in short means using special materials to make semi-permeable membrane , allowing the substance to selectively pass through , so as to achieve the effect of desalination. This method originated in the 1950s and began to be commercially used in the 1970s.
According to the data, the basic principle of reverse osmosis is to overcome the phenomenon of natural osmosis through pressure drive . After pretreatment, the seawater will be moved to the freshwater through the semi-permeable membrane, and the salt and other substances will remain on the seawater, and the filtration target will be completed under the extremely low energy consumption.
research shows that the mechanism of water passing through the semipermeable membrane is that the ability of water molecules to diffuse through the hydrophilic semipermeable membrane is much stronger than that of salt and other components in seawater, which is also the essence of semipermeable membrane semipermeability.
Typical membrane method seawater desalination process schematic diagram
It is not difficult to see that in the reverse osmosis method, the most important thing about is to have semi-permeable membrane . If the semi-permeable membrane is good, the efficiency of seawater desalination will definitely be improved. Therefore, scientists' new discoveries are also in this field.
During the research process, scientists found that the key to improving efficiency is not how thin the membrane is. is to make the density of the semi-permeable membrane reach the nano-level, and to make the entire density of the semi-permeable membrane "evenness and consistency" .
In this case, its filtering effect has been improved, and the overall efficiency of has been improved by about 40% .
Schematic diagram of semi-permeable membrane filtering small molecules
Therefore, they put forward suggestions for improvement. In order to improve the efficiency of seawater desalination, people should focus on promoting uniform density of semi-permeable membranes , rather than just thinking about how to thin it.
, a chemical engineer at Penn State University, said: "You can see with your own eyes that the density is high or low in certain places in the coffee filter. In the filter membrane, it looks uniform, but not nanometers, and how to control the mass distribution is really important for water filtration performance."
conceptual diagram of semi-permeable membrane
Gomez, a chemical engineer at Penn State University, said: "you can see with your own eyes that the density of some places in the coffee filter is high or low. In the filter membrane, it looks uniform, but not nanometers, and how to control the mass distribution is really important for water filtration performance."
Concept diagram of semi-permeable membrane
Give a similar example to facilitate everyone's understanding. The "efficiency" of fishing nets with large mesh and small mesh fishing nets must be different when fishing. And if you only pay attention to whether the fishing net is thin enough, and ignores whether there are inconsistent mesh areas in each part , then even if you catch the fish, the fish can slip away from the large mesh. In this way, we will still be in vain.
In addition, researchers who disclosed this research results said that if the semi-permeable membrane is improved in this way, can also save as much money as possible for large companies, making the cost of desalination of seawater lower . In this way, the crisis problem of freshwater resources can be better solved.
Large seawater desalination factory
Since it is expected to use nano-level methods to improve the semi-permeable membrane, increasing the probability of seawater desalination by 40%, does this mean that our problem of shortage of freshwater resources has been completely solved? In the future, we will no longer have to worry about the exhaustion of fresh water?
Purpose and prospects of seawater desalination
In fact, the advancement of seawater desalination can only replenish freshwater resources and play the effect of "icing on the cake" . If everyone thinks that seawater desalination can directly bear all freshwater consumption, it would be a bit "blindly optimistic".
At present, seawater still finds it difficult to fully "support" fresh water
. Because no matter how the efficiency of seawater desalination is improved, its cost is still very large. And generally speaking, the water after seawater desalination is still unavailable directly, and still needs further processing and .
According to the data, in 2018, the global seawater desalination capacity was 6.2×10^7m3/d. Except for municipal water use, the rest of is concentrated in the industrial field . Even so, still has a large population facing the crisis of water shortage .
Global water intake diagram
You should know that seawater desalination plants are not charitable organizations after all, and they also need to make profits. Not to mention, in the case of high cost reduction, we will go to "Generate Power for Love" to help areas with water shortages.
To sum up, it is still relatively naive to think that the current seawater desalination can help us solve all problems. And since traditional seawater desalination methods still produce pollution and waste , people are exploring a new path to try to further develop new seawater desalination technology.
Seawater desalination technology still needs to continue to improve
In short, seawater desalination technology can indeed bring us certain benefits, , but humans still need to protect and cherish freshwater resources , especially under the influence of global warming , freshwater resources may become less and less in the future.
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