Water covers 70% of our planet, but fresh water for human consumption is scarce, comprising only 3%. And two-thirds of that fresh water is not available, as it’s either ice or is inaccessible. That poses a substantial problem because clean, fresh water is critical for sustaining human life. In July 2021, findings from the Joint Monitoring Programme (JMP) report stated that by 2030, only 81% of the world’s population will have access to safe drinking water at home; 1.6 billion will be without. Moreover, approximately 2.7 billion suffer scarcity at least one month per year. Those statistics have raised alarm bells and have driven the search for solutions, one of which is not entirely new: desalination.
What is Desalination?
Desalination is the process of removing minerals (mostly salt) from seawater through physical and chemical processes to make it drinkable. Desalinated water is used on many seagoing ships and submarines, and water-scarce regions are particularly reliant on the technology. In fact, desalination provides the United Arab Emirates with 42% of its water needs.
Most of the modern interest in desalination is focused on cost-effective provision of fresh water for human use. Along with recycled wastewater, it is one of the few rainfall-independent water resources.
Due to the minimal cost of pumping, desalination is most economical in large coastal locations. However, our changing climate, which has brought about widespread drought, is contributing to increasing water shortages in typically mild regions, necessitating the expansion of desalination plants further inland and from brackish water. China, the U.S., and South America are all expanding their desalination capacity.
In the summer of 2022, drought was declared in many parts of the US and the UK following low rainfall and high temperatures. This resulted in restrictions from water companies, including bans on watering lawns and washing cars.
Drought in other parts of the world have led to more fatal consequences. East Africa, in particular, is facing its worst drought in years. By August 2022, over one million people had become displaced due to extreme drought in Somalia alone. In fact, drought has affected more people in the last 40 years than any other natural disaster. So, the need for clean, fresh water is critically high.
Types of Desalination
Desalination is accomplished in five main ways. In thermal desalination, heat is used to produce water vapor that condenses on pipes into fresh water. This process remains dominant across the Middle East, where nearly half of the world’s desalinated water is produced.
Membrane desalination, used in 60% of plants worldwide, is more commonly referred to as “reverse osmosis.” Saline water is forced under high pressure through a semi-permeable membrane whose pores are too small for the salt molecules to pass through.
Imitating the water cycle, solar distillation consists of evaporating seawater in large facilities with roofs where it is condensed and collected as fresh water. Although the energy used is the sun’s heat, large areas of land are required.
Electrodialysis consists of moving the salt water through electrically-charged membranes that trap the salt ions dissolved in the water, allowing fresh water to be extracted. There are diverse variants of electrodialysis, such as conventional and reverse.
Nanofiltration is a process that uses nanotube membranes that are more permeable than reverse osmosis membranes, which means that more water can be processed in less space and using less energy. These membranes are manufactured with sulfonated compounds which, in addition to salt, eliminate traces of pollutants.
Global Desalination Statistics
According to a study conducted by researchers from the Institute for Water, Environment and Health at the United Nations University (UNU-INWE) in 2019, there are approximately 16,000 desalination plants in operation, spread throughout 177 countries. Altogether, they generate around 95 million cubic meters per day of fresh water — equal to almost half the average flow over Niagara Falls. The first country to adopt this process en masse was Australia, a very arid country where the so-called Millennium Drought, between 1997 and 2009, wreaked havoc. Plants in Australia’s main cities operate through reverse osmosis.
Several countries, such as Bahamas, Maldives and Malta, meet all their water needs through the desalination process. Saudi Arabia gets 50% of its drinking water from desalination. The United Arab Emirates is another desert country that is highly dependent on desalination. Other countries in the Middle East, such as Kuwait and Qatar, have also opted for it.
In the United States, third in this particular ranking, there are desalination micro-plants close to almost all the natural gas facilities to exploit the residual heat.
Spain is fourth, thanks to the contribution of the Canary Islands and the Alicante and Murcia coast, where the old thermal power plants are being replaced by desalination plants.
Desalination Challenges and Environmental Impact
While desalination technology may be capable of countering global water shortages, there are issues regarding its cost and efficiency. Desalination is expensive because large amounts of energy are required to drive the process. This is particularly true for thermal desalination, where energy costs represent up to half of a plant’s entire production cost.
Another desalination challenge is its impact on the environment, particularly marine life. For every liter of freshwater output, desalination plants produce on average 1.5 liters of brine (though values vary dramatically, depending on the feedwater salinity and desalination technology used, and local conditions). Globally, desalination plants now discharge 142 million cubic meters of hypersaline brine (industrial waste-water with salt levels that exceed even that of seawater) every day — a 50% increase over previous assessments. That’s enough in one year (51.8 billion cubic meters) to cover Florida with 30.5cm (1 foot) of brine.
Desalination plants near the ocean (almost 80% of brine is produced within 10 km of a coastline) most often discharge untreated waste brine directly back into the marine environment. The brine greatly raises the salinity of the receiving seawater, which poses major risks to ocean life and marine ecosystems. Toxic chemicals used as anti-scalants and anti-foulants in the desalination process (copper and chlorine are of major concern) are also polluting the oceans.
Further, brine underflows deplete dissolved oxygen in the receiving waters. High salinity and reduced dissolved oxygen levels can have profound impacts on benthic organisms, which can translate into ecological effects observable throughout the food chain, according to the UNU-INWE’s 2019 report.
Excellent article.
The United States has immense amounts of fresh water. Overall, we have no shortage. The issue that the water isn’t always near where we would like it to be.
It still seems that the best sources of fresh water are from major rivers, such as the Columbia, Mississippi and St. Lawrence Rivers. Capture a portion of the fresh water headed out to sea and you can pipe that to wherever it’s needed, such as California or Arizona. With large enough pipes and slow enough velocities, the operating cost can be very reasonable. Not free, but possibly far less than desalinization.
We have a nationwide network of oil and natural gas pipelines which show it can be done.
Have any of these installations been operating long enough to see the salinity of the intake water rise enough, due to discharges of brine into the source water, to adversely impact the performance of the desalination plant? Or is the changeover of the intake water from tides and ocean currents enough to prevent this adverse effect from impacting performance?
Well written and researched.