Desalination plants generate as much brine as to cover Spain

A report from the United Nations University (UNU) has encrypted the number of desalination plants on the planet. The work shows the amount of drinking water they generate and alleviates the thirst of millions of people. But it also reveals the millions of cubic meters (M3) of hypersaline water (brine) generated in the process. Although most plants are found in the west, only four countries in the Persian Gulf produce more than half of the brine, which they throw directly into the sea.

The study is part of a reality: 40% of the population suffers from water shortages. The problem will worsen in the future by two growing trends. On the one hand, there is the expected increase in population and, on the other, anthropogenic factors such as pollution and climate change will further reduce the availability of water from conventional sources. That is why we will have to look for it where there is more: in the sea.

The UNU Scientists review estimates that there are 15,906 operational desalination plants (the figure includes those under construction). This number implies almost three-fold the existing ones at the beginning of the century. In addition, they have a theoretical capacity to generate potable water (the real one is impossible to calculate) of about 95 million of cubic meters per day (M3/day), about 34 billion a year. 70% of the plants are in rich countries and 0.1% in the 100 poorest. Among the first are the USA with 10% or Spain with 5.7% (more than half of the desalination plants in Europe). But the largest concentration is in the Persian Gulf: Saudi Arabia, Kuwait, and Qatar are hogging a third of the facilities.

The work, published in Science of the Total Environment, also determines the uses that are given to desalinated water, sources of origin or technologies used for POTABILIZARLA. Most of the water (62.3%) is destined for direct human consumption and another third for industrial use, since many processes need water with low concentration of salts. Almost two-thirds of the water is obtained from the sea and another quarter of brackish water inland. The dominant technology today is reverse osmosis, where the water is separated from the salts by the use of membranes. Almost 70% of the water is obtained in this way. The other main technologies, with a quarter of the water produced, are thermals, which use evaporation and condensation processes.

Saudi Arabia, Kuwait, UAE and Qatar produce 55% of brine but only one-third of desalinated water

The biggest problem of desalination plants is, according to this new work, brine. So far it was accepted that, in global terms, the conversion ratio was close to 0.50. In other words, to produce a liter of drinking water, another brine was generated. The logic is simple: if the average concentration of salts in sea water is 30/35 grams per liter and one you take away all the salt, you have another with 60/70 grams of salts.

However, the reality that reveals this study is very different. Every day, in the world, desalination plants generate 141.5 million of M3 Brine. It's 50% more than we thought. A year is about 51.7 billion m3, enough to cover the extension of Spain with a thin layer of hypersaline water. So to produce a liter of drinking water, you have to generate 1.5 liters of brine.

The geographical distribution of responsibility is very unequal: 55% of all this brine is produced in Saudi Arabia, UAE, Kuwait and Qatar. However, the plants of these ancient desert countries only produce one third of the water. It is true that oil states need desalinated water to cover up to 100% of their needs, but this work also reveals its enormous inefficiency to achieve it.

Distribución de las 16.000 desaladoras. El color indica la fuente del agua y las figuras geométricas, la tecnología usada.Extend photo distribution of the 16,000 desalination plants. The color indicates the water source and the geometric figures, the technology used. UNU-INWEH

"These countries need to review the strategies for managing brine," says the assistant director of the Institute for Water, Environment and health at UNU and co-author of the study, Manzoor Qadir, in a post. In particular, it is urgent to devote greater research efforts to achieve, on the one hand, "to reduce the volume of brine generated, for example, by increasing the efficiency of the desalination process" and, on the other, "to treat and/or use brine so that it is Economically viable and respectful of environment fear, "he adds.

It should be noted that the article mentions two studies in which a thorough revision of the techniques, technologies and recent innovations in the management of the brine, one of them of Professor José Morillo of the University of Seville, is carried out. For Morillo, the key is to turn brine into an opportunity. "In the 60 grams of salts per liter, there is sodium chloride, but also lithium or magnesium," he recalls. Both magnesium and lithium are highly valued metals, especially in the technological sector. The team of this teacher, in collaboration with Professor Alfonso Caballero (Seville Institute of Materials Science) and companies such as Abengoa, has carried out several tests to recover mineral ores. They are jobs that are in the beginning, but, to be fruitful, would turn a problem into a great opportunity.

The margin of improvement is enormous. The Gulf countries were the first to install desalination plants more than half a century ago. Supported by cheap oil, they bet on thermal technologies, which use energy to evaporate and condense water. But today they have been surpassed by other systems. According to industry experts, to achieve a cubic metre of desalinated water need 10 times more energy than a desalination plant by reverse osmosis of Spain. Although in the conversion ratio the origin of the water also intervenes (the marinas have higher concentration of salts than the brackish or of river) and not only the technology, the plants of the Middle East have conversion ratios that rarely exceed the 0.25, half that their equiv In Europe and up to a tenth of that of some of the plants for industrial use.

A liter of brine has about 60 grams of mineral salts, some with great commercial interest, such as lithium or magnesium.

Although the study does not go into the environmental impact of such brine, Qadir recalls how different studies have pointed out that "the increase in salinity and temperature due to brine discharge can cause a decrease in dissolved oxygen content, which is Known as hypoxia. " The big problem is that while the desalination plants have to comply with a very demanding regulation to reduce this brine, which are nourished by sea water, the only viable option for now is to return the water to the sea with the extra salts with the risk posed by PA RA the middle.

"In Spain the most affected species are Posidonia oceanica, Cymodea nodosa or zostera noltii, which are aquatic grasslands, some of them endemic to the Mediterranean and protected," says the researcher at the Institute of Environmental hydraulics of the University of Cantabria, Íñigo Losada, not related to the study. "There are also algae or molluscs that may be affected. In general, although it can also affect fish, they usually leave the landfill area when conditions are not adequate, he adds. It remains to be known whether, although these effects are local, the large number of desalination and brine that they produce will eventually become a global problem.

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