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Scientific American
a day ago
- Science
- Scientific American
Deep-Sea Desalination Pulls Drinking Water from the Depths
From Cape Town to Tehran to Lima to Phoenix, dozens of cities across the globe have experienced water shortages recently. And in the next five years the world's demand for fresh water could significantly outpace supply, according to a United Nations forecast. Now several companies are turning to an unexpected source for a solution: the bottom of the ocean. Called subsea desalination, the idea is to remove the salt from water in the deep sea. If it worked at scale, the technology could greatly alleviate the world's water access problems. Costs and energy requirements have kept desalination from going mainstream in most of the world. Early desalination involved boiling seawater and condensing the steam, a purely thermal method that used loads of energy. This approach was later replaced by multistage flash distillation, in which temperature and pressure 'flash' salt water to steam. In the past 25 years reverse osmosis has become more common—it uses high pressure to push seawater through a membrane with holes so small that only water molecules squeeze through, leaving salt behind. On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. Reverse osmosis is more efficient than distillation, but it takes a lot of energy to pressurize millions of gallons of seawater and move it through filters. What if we could let that movement happen naturally by harnessing the pressure hundreds of meters underwater? That's the idea behind subsea desalination. Reverse osmosis pods are submerged to depths of around 500 meters (1,600 feet), where immense hydrostatic pressure does the heavy lifting of separating water from salt. Purified water is then pumped back to shore. Far-fetched as it may sound, there are multiple prototypes already at work; the companies behind them aim to take cheap, large-scale desalination from pipe dream to reality. One of these companies is Oslo-based Flocean. Its founder and CEO, Alexander Fuglesang, says there's no revolutionary new technology behind his business; it's 'essentially a subsea pump cleverly coupled to existing membrane and filter technology,' he says. What's new is the energy savings—Flocean uses 40 to 50 percent less energy than conventional plants—and modular systems that can be deployed to many deep-sea location without bespoke engineering. The seafloor has other benefits, too. This region harbors fewer bacteria and other microorganisms than at shallower depths, and there is little local variation in temperature or pressure. 'The deep sea is really predictable,' Fuglesang says. 'It's the same 365 days a year.' This isn't the case at land-based plants, which have to deal with algae blooms, river runoff, storms and seasonal temperature changes. Plus, less chemical pretreatment of the water is needed at depth, and because the equipment is all underwater, there's no 'not in my backyard' controversy over putting big, unsightly infrastructure near the seashore. Despite its advantages over land-based plants, subsea desalination has several hurdles to clear before scaling to commercial levels. For starters, it's still too expensive. Land-based desalination is several times more costly than pulling water from aquifers or lakes, even at giga-plants in the Middle East that benefit from abundant solar power and large economies of scale. Even if subsea technology cuts the cost of land-based desalination down by 40 percent, it will still be a pricey way to obtain potable water. 'We need to remember that once the water is desalinated, it still needs to be pumped up from depths of up to 600 meters,' says Nidal Hilal, founding director of New York University's Water Research Center in Abu Dhabi, who has studied water-treatment engineering for more than 30 years. 'Early pilot tests show promise, but the technology has yet to be proven at large scale.' Affordable renewable energy will make subsea desalination more viable. Improvements in technology will also help. Hilal's research group, for example, is developing electrically conductive reverse osmosis membranes that keep themselves clean by repelling salt ions and impurities. They would extend maintenance intervals, which Fuglesang says might be two to three years with existing membranes. Although proponents of the technology say it would have little effect on undersea life, others urge further research to gauge its impact on marine ecosystems. 'Many organisms thrive at a 500-meter depth,' says Adina Paytan, a professor affiliated with the Institute of Marine Sciences at the University of California, Santa Cruz. The twilight zone—which extends from 200 to 1,000 meters below the surface—is not only home to organisms such as whales, squid and jellyfish. 'It's extremely important for many ocean processes such as the carbon cycle and nutrient cycling,' Paytan says. Companies will need to ensure that their water intake and salty brine by-product don't harm marine life or significantly alter these processes. Given the depths required, subsea desalination won't work in just any seaside location. 'Many coastal cities lie on wide continental shelves, meaning deep water is far offshore,' Hilal says. Coastlines with steep drop-offs are ideal because shallow shelves would require long pipelines, adding to capital and operational costs. Fuglesang isn't worried about technical or engineering hurdles; he says the industry's biggest challenge will be aligning customers, governments and financial partners. Flocean is working on what will be the world's first large-scale subsea desalination plant, off the coast of Norway, and has a contract to start supplying water to an industrial facility in 2026. Netherlands-based Waterise has also secured its first industrial customer, with plans to start building a plant in the Red Sea's Gulf of Aqaba later this year, and Bay Area–based OceanWell is testing its prototype near Los Angeles. Long-term government contracts will most likely be needed for subsea desalination to really take off, and they may prove elusive. 'The water-infrastructure industry is quite conservative,' Fuglesang says, noting that because new projects are so expensive, 'nobody wants to be first' to go all-in on a new technology. Hilal says he believes subsea desalination could go mainstream and supply water to entire cities. But, he adds, 'reaching true city-scale will take time, conceivably a decade or more.'
Forbes
08-05-2025
- Business
- Forbes
Investing In The Life-Saving Technology Of Desalination
U.S. Army Sergeant Kornelia Rachwal gives a young Pakistani girl a drink of water on the 19 October ... More 2005 after the Kashmir Earthquake. Desalination is an important tool in disasters. After an attack on tourists in the divided state of Jammu and Kashmir, the Indian government said it was suspending a water sharing treaty with Pakistan, bringing the two nuclear-armed powers to the brink of war. Mexico's president, Claudia Sheinbaum, acceded to Trump Administration demands that her country deliver an enormous amount of water to Texas farmers, at the expense of Mexican farmers suffering from a long, severe drought. These global headlines underscore the increasing importance of desalination technologies in a warming world. Since my December 2024 article, Flocean's Deepwater Desalination Reforms A Vital But Costly Industry, I've done a good bit of research on desalination technology. My research convinced me that desalination will become increasingly vital the further we move into the post-Climate 21st century. Here are the trends I see: According to a recent Bank of America analysis, the desalination market was worth $15.2 billion in 2022 and is projected to grow at an annual rate of 10.5%, reaching $33.4 billion by 2030. The Age of Exploration would not have been possible without desalination aboard ships transiting to the Americas and the Spice Islands. Onboard stills boiled saltwater and captured the fresh condensate. After World War Two, Middle Eastern countries, flush with oil and the cash that came with it, built huge, oil-burning desalination plants based on the same principles as the shipborne stills. This technological pathway, called thermal desalination, was dominant until around 2000 and comes in two flavors: Multi-Stage Flash and Multi-Effect Distillation. MSF is the easiest to scale and was thus the dominant technology in the Middle East for years. It is phenomenally energy-intensive but can be made less so if paired with electricity generation. MED is much more energy efficient but harder to scale, so these plants are usually used on remote islands with limited fuel resources. Multi Stage Flash Desalination Plant at Jebel Ali G Station (Dubai), taken in 1994. Research into membrane-based desalination using reverse osmosis began in the U.S. in the 1950s in response to a local drought in California. Spain's arid climate and lack of domestic fossil fuel resources focused national R&D programs on RO desalination. This technology uses powerful electric pumps to push seawater through special membranes that allow freshwater to pass through while blocking salt. The price of desalinated water decreased about 45% between 2012 and 2022, according to a 2023 analysis by Utah Tech University professor Gale L. Pooley. Improvements to RO systems, especially modularization and energy recovery, were a big factor in this price reduction. While climate change threatens the freshwater resources humans rely on, the carbon footprint and other ecological impacts of conventional desalination methods exacerbate climate change and ecosystem loss. Energy consumption is the main driver behind desalination's carbon footprint. Desalination, whether by burning fossil fuels to boil water or using electricity to force water through a membrane, requires a lot of energy. CO₂ emissions from desalination facilities are substantial, estimated to be around 120 million tons annually. Extrapolating the growth of desalination services over the next several decades, the carbon footprint of providing freshwater globally could reach 218 million tons by 2040 and 400 million by 2050. Seawater is typically drawn from the top 20 meters of the sea, which is teeming with biological activity. The first step in both thermal and RO desalination is to filter and chemically treat the seawater with biocides and coagulants to remove organics. After the desalination process is finished, highly concentrated brine and chemical waste is released into offshore tidewaters, wreaking havoc with sensitive coastal ecosystems. Another ecological impact that cannot be overlooked is onshore land use. Desalination plants can take up a lot of real estate, crowding out other agricultural or other potential users. There are some very large legacy players in the desalination business, including French Veolia Water Technologies (a subsidiary of Veolia Environment and acquirer of Suez), Korean firms Doosan Enerbility and GS Inima, Spanish firms Abengoa, Acciona Agua, and Aqualia, and Israeli firm IDE Technologies. These companies have staked out geographical territories and technical competencies and are focused on designing, building, and sometimes operating the largest desalination plants on earth, some generating millions of cubic meters of freshwater per day. I am more excited about smaller, modular competitors, especially because smaller companies are finding creative ways to reduce desalination's ecological impact. Several years ago, Metito, a Middle Eastern company, outfitted barges with modular RO desalination equipment and supplied them to the Saudi Water Authority, the largest buyer of desalination services in the world. Since then, other floating desal projects have been discussed for regional water shortages in Spain and elsewhere. I spoke with the CEO of a Norwegian firm, EnviroNor, which repurposes decommissioned freighters with desalination equipment to service the needs of coastal communities. EnviroNor has teamed up with Japanese shipping and logistics giant Mitsui OSK Lines to commercialize this business, and the team is actively bidding projects. Barge-based desalination solves land-use issues and expels waste in offshore waters that dilute it more readily, but most of the ecological issues associated with desalination are still evident, since shipborne desalination still requires the same amount of energy and chemicals to run as legacy systems. The Canadian firm Oneka and the Norwegian firm Ocean Oasis are working on modular, floating desalination buoys that use wave power to provide low-carbon-footprint freshwater to coastal communities. In answer to written questions, Oneka's CEO told me that the company started with smaller projects, oftentimes benefiting remote coastal communities, but intends to scale up to an output of up to 10,000 cubic meters per day by adding modular desalination units. Clearly, this solution greatly reduces the carbon footprint of a desalination project, since desalination's energy requirements are provided by renewable wave power. It also reduces pressure to use valuable land and expels brine and chemicals offshore, rather than in sensitive ecological tidewaters. This approach's biggest drawback in my mind is scalability, especially within the engineering difficulties associated with the rough offshore environment. The buoys are relatively small and light, so storms and high waves must play havoc with their anchoring and piping systems and the actual desalination equipment. Three firms are taking the lead in this field: Flocean and Waterise from Norway and OceanWell from the U.S. Of these, Flocean looks to be the most commercially and technically advanced, having already conducted a commercial pilot in the Red Sea and, according to CEO Alexander Fuselang, is closing in on further commercial announcements. Waterise has announced partnerships and memoranda of understanding, but seems to still be waiting for approval to start a commercial pilot. OceanWell is focused on the U.S. market and announced a pilot project off the coast of southern California, but is also awaiting permitting approval. I like subsea desalination for its attenuation of ecological harm and its readiness to scale. Subsea RO desalination, performed at around 500 meters below the surface, uses the enormous weight of the water column to push saltwater through membranes, resulting in a 35%-50% reduction in desalinization's energy requirements. This energy might be supplied by wave power or on-shore solar or wind, reducing the carbon footprint even further. Also, intake water is drawn from deeper than the level which sunlight can penetrate, so biological activity and organic matter is extremely low, requiring less harsh chemical pretreatments that wind up as toxic waste. The brine can be dispersed over the sea floor and diluted by currents. The downside of subsea desalination is that servicing units is not as straightforward as sending someone aft with a wrench. That said, periodic servicing of Flocean's desalination modules can be done using the same equipment and techniques as for subsea oil and gas equipment. The company also includes redundancies in its planned modular facilities. Each desalination operation will have eight modular units, one of which is 'hot-swappable,' held in reserve in case another unit malfunctions or needs to be serviced. Human habitation wouldn't be possible in some parts of the world without desalination. As the climate heats up, soils dry up, more people move to coastal urban centers, and more water is used for industrial and agricultural purposes, desalination will only become more important. If you are interested in a more in-depth picture of the supply/demand dynamics of the desalination market and want to learn more about Flocean's approach to desalination, please take a look at the detailed research report I just published. I received a message from a contact in Spain who recounted her shock when her tap ran dry during the recent blackout. It does not require too great a leap in this post-Climate world to imagine a dry tap becoming a daily or weekly occurrence rather than a one-off, and that mental experiment piques my interest in desalination. Intelligent investors take note.
