Desalination of water, a solution to climate change
One of the largest desalination plants in the world is located in California and transforms every day, by filtration, more than 380,000 m3 of sea water to produce about 190,000 m3 of drinking water, which represents about 10% of the drinking water consumed by 3.1 million inhabitants.
Although the cost of the water produced in this way is twice as high as with a traditional supply, this plant is essential to ensure, in years of drought, a continuous local supply, without having to import water. It is thus planned to develop 10 plants of this type in California, in addition to the 10 existing plants.
Desalination to obtain drinking water is developing more and more because of the increase in population in areas where freshwater is becoming scarce, such as California, certain regions of China or India, for example, and the number of areas concerned is increasing regularly because this phenomenon is accentuated by climate change and periods of drought, as in the case of California, which can rely less and less on the flows of the Colorado River.
At the same time, the costs related to the exploitation of drinking water in a traditional way are tending to increase and those of desalination to decrease due to technological developments, in particular, desalination is becoming more and more attractive.
This reverse osmosis process requires constant pressure to dissociate the salt from the water and therefore uses a lot of energy, the cost of which is included in the cost price of the water. Fossil fuels are the main source of energy to implement this process, and desalination generates a significant amount of carbon dioxide. Solar energy remains little used because it requires large storage capacities in batteries to ensure the continuity of the process in all types of weather.
In 2014, a new and more ecological process was discovered by the Frenchman Marc Vergnet and allows both to desalinate water without releasing carbon dioxide and to produce brines with half the salt concentration of the traditional process. The principle of this discovery is to be able to adapt the pressure exerted on the water.
By using photovoltaic energy, it is no longer necessary to exert a constant pressure but to vary this pressure according to the sunshine thanks to sensors. The membranes will decide when they need pressure and how much power is required. The cost of producing fresh water is 1.5€/m3, which is half the price of using fossil fuels.
This invention is primarily dedicated to small cities in less developed countries or to islands suffering from a chronic lack of water.
The challenge of desalination is to be able to propose processes that are more ecological, less energy consuming and can be adapted on a large scale. Taking the environment into account means reducing carbon dioxide emissions into the atmosphere and reducing brine discharges, which are a major source of pollution for the seas and oceans into which they are discharged.
A new, more economical technology, developed by Korean researchers, consists of separating two pockets by a hydrophobic membrane that allows only water vapor to pass through. The process no longer needs to use reverse osmosis because the seawater in one of the pockets is heated and the water vapor released is collected in the second pocket, which is made up solely of fresh water.
The use of a new type of membrane, made of two materials sprayed one against the other and no longer woven together, according to the coaxial electrospinning technique, increases the life span compared to traditional membranes and therefore requires less frequent replacements.
Another technology, developed by French researchers, can desalinate three times more water and consume 12% less energy than traditional methods. The system consists of a hybrid membrane composed of a polyamide membrane and artificial water channels.
The development of this new system is based on the way in which proteins, the aquaporins, in polyamide membranes, which form channels permeable to water and which reject ions, have been operating since the 2010s. The innovation consisted in reproducing these channels synthetically, less expensive than the production of natural aquaporins.
The artificial water channels are then inserted between layers of fat, which facilitates transport and requires less energy input. In this way, artificial water channels of nanometric dimensions can be used to produce square meters of membranes and millions of cubic meters of desalinated water per day.
All of the technological innovations that affect water desalination, whether they are new membranes with a longer life span, less energy consumption, limiting brine discharge or better productivity, with a greatly reduced size, are encouraging solutions to the shortage of drinking water, which should only increase in the coming years with climate change.