According to foreign media New Atlas, although more than 70% of the earth ’s surface is covered by water, it is frustrating that most of it is not drinkable. Seawater desalination is an important technology that can help to obtain more drinking water. Now two independent teams have developed a new type of solar water desalination system using very different mechanisms.
The first of these two new designs comes from researchers at MIT and Shanghai Jiaotong University. The team said that the overall efficiency of the multi-layer system is as high as 385%, and each square meter of solar energy collection area can produce up to 5.78 liters of purified water, which is more than double the output of similar systems.
Each layer arranged vertically plays an important role in this process. First, there is a transparent insulating layer that allows direct sunlight to the black heat-absorbing layer. The heat is transferred to several layers of wicking material in turn, and the wicking material sucks up the water from below. Water evaporates from this layer and hits another surface, condenses on this surface and drips down for collection.
The team said that most of the efficiency comes from ways to save heat. Heat is not lost to the environment, but is transferred to each evaporation layer in turn. The salt stays in the wicking material and can obviously be removed naturally at night. When the equipment cools, the salt will diffuse back into the seawater.
However, the second system designed by researchers from the University of Bath, the University of Johannesburg and the Bogor Agricultural University in Indonesia uses a very different mechanism. The device does not move water through the membrane and leaves salt, but instead separates the salt from the water. This feat can be achieved using the ion system. Separating the two chambers is a thin synthetic semipermeable membrane that only allows salt ions to flow in one direction. This is because the membrane is negatively charged and coupled with an anion resistor, so only when current is applied, the negative ions of the salt can pass through. This current need not be too strong, but can come from solar energy.
After opening, the salt is extracted from one chamber and deposited in the other chamber. The team said that unlike the first system that returned the remaining material to the sea, the salt could be collected for other uses.
The researchers of both projects stated that these two designs are very useful for small water desalination, possibly in portable devices. This means that they can be deployed in developing countries or disaster areas to provide drinking water without conventional infrastructure.
The design of MIT is described in a paper published in the journal Energy and Environmental Science. The second study was published in the journal Desalination.
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