Drinking water from the sea? | Knowledge & Environment | DW
Although 70 percent of the earth’s surface is covered with water, only 1 percent of it is potable. In addition, freshwater, a finite resource, is distributed very unevenly. In hot and arid regions of the world, where the population is growing along with the standard of living, there is not enough water for everyone. A situation that is being exacerbated by climate change. Exotic approaches already exist in the fight against drought, such as “iceberg harvesting,” which involves towing icebergs and turning them into drinking water, or generating rain at the touch of a button by injecting chemicals into clouds. But they have not yet been able to prove themselves on a large scale.
The desalination of seawater has therefore become one of the few real and viable options for regions suffering from water stress to combat the drought can arm. The idea itself is centuries old. Today, on the one hand, there is the approach of thermal desalination and reverse osmosis. In the former, the water is evaporated and distilled, in the latter, salt and water are separated from each other by a membrane. There are currently over 20,000 desalination plants in operation in more than 170 countries worldwide – the ten largest are in Saudi Arabia, the United States, Israel and the United Arab Emirates (UAE).
New water sources are essential
Almost half of the fresh water from seawater desalination is obtained in the Middle East and North Africa Manzoor Qadir, Vice Chair of the United Nations University for Water, Environment and Health. These arid areas have few other sources of water and rely on seawater desalination. According to Qadir, they have less than 500 cubic meters per capita available annually through rain or other runoff. That’s about three times less than in the US.
Water poverty will continue to worsen with population growth and rising temperatures, with sub-Saharan Africa likely to become “a water scarcity hotspot” by 2050, according to Qadir. Desalinating seawater is a good opportunity to use existing resources, also because the costs “have fallen dramatically,” says Qadir – from around five dollars per cubic meter in 2000 to the current average of 50 cents. “You don’t have to think long about it,” he says Frithjof C. Kuepper from the Department of Biodiversity at the University of Aberdeen and an expert on the subject of “environmental impacts from desalination plants” in Cyprus. “For countries like Cyprus, there is no other option if they want to maintain their standard of living.”
In the Republic of Cyprus, the warmest and driest country in the EU, 80 percent of drinking water comes from seawater desalination, says Kuepper. As early as the 1990s, fluctuating rainfall led to water shortages. At that time, the Cypriot government initially tried to balance the deficit by importing water from Greece. “But that cost ten times more than desalinating the water,” Kuepper continues. That’s why the government started building desalination plants in the early 2000s. Water scarcity should be avoided in this way.
Consequences for the seas and the climate
Both Kuepper and Qadir acknowledge that the supposed silver bullet against water scarcity in its current form poses serious environmental problems. One reason is that the process consumes a lot of energy. In Cyprus alone, desalination plants are responsible for around two percent of total greenhouse gas emissions and five percent of electricity consumption. This makes it one of the most power-intensive sectors in the country.
Another problem is the toxic brine, a highly concentrated salty seawater residue, that is produced during the process. The mixture has a significantly higher salt content than seawater, but is often returned to the sea. There it can cause considerable damage to coastal ecosystems. One co-authored by Manzoor Qadir report shows that high salinity, together with the climate-related rise in temperature in the water, can lead to lower oxygen levels. This results in what is known as hypoxia, a lack of oxygen. This highly saline water can sink to the seabed and kill microorganisms in the water that are vital to the entire food chain. Chemical compounds such as copper and chloride are also used in the desalination process, which the report says can be toxic to organisms in the water.
How can desalination become sustainable?
According to the authors of the study, the solution to the high CO2 emissions is to use wind and solar energy to power desalination plants. The Berlin company Boreal Light, for example, has developed desalination plants that are completely renewable energies feed and produce independently of the power grid and developments in electricity prices. “The water is free, the electricity is free from wind and sun. This allows us 1000 liters [frisches Wasser] produce for 50 cents,” Ali Al-Hakim, co-founder of Boreal Light, told DW. According to Al-Hakim, their supply and prices for a cubic meter of water can compete with the prices of fresh water from rivers or wells.
According to Kuepper, the excreted toxic brine could also be discharged into the sea with special pipes where it causes less damage. However, it is better to leave the waste on land. One Study from 2019 shows how sodium, magnesium, calcium, potassium, bromine, strontium, lithium, rubidium and uranium could be extracted from the filtered material and reused in industry and agriculture. However, the extraction of these resources is not economically competitive, says Qadir. This needs to change, as reuse is an important sustainable solution, he adds. Especially “in countries that produce large amounts of brine with relatively low efficiency, such as Saudi Arabia, UAE, Kuwait and Qatar“.
A villager fetches drinking water from a water desalination plant in Bonbibi Tala in Satkhira, Bangladesh
Recycling seawater brine?
Scientists at the US research institution Massachusetts Institute of Technology (MIT) have suggested ways to reuse brine by using the salt to make caustic soda or caustic soda. According to Qadir, the latest water treatment processes are still in their infancy, but the newest and most modern plants in the USA are already producing less brine.
About 12 percent of the world’s desalinated water comes from the United States, but only 4 percent of the world’s brine, Qadir explains. In contrast, half of all desalinated water comes from regions in the Middle East and North Africa. Since some of the systems there are not as efficient and modern, 70 percent of all brine worldwide comes from these regions. With improved technology, the impact on the climate and the environment will decrease, according to Qadir. For Kuepper there will be no way around desalination in the future. “Our job is to make sure it’s sustainable.”
Adapted from the English by Tim Schauenberg.
