Aurelia Butler

Today, 2.2 billion people in the world lack access to safe drinking water. In the United States, more than 46 million people experience water insecurity, living with either no running water or water that is unsafe to drink. The increasing need for drinking water is stretching traditional resources such as rivers, lakes, and reservoirs.To improve access to safe and affordable drinking water, MIT engineers are tapping into an unconventional source: the air. The Earth’s atmosphere contains millions of billions of gallons of water in the form of vapor. If this vapor can be efficiently captured and condensed, it could supply clean drinking water in places where traditional water resources are inaccessible.With that goal in mind, the MIT team has developed and tested a new atmospheric water harvester and shown that it efficiently captures water vapor and produces safe drinking water across a range of relative humidities, including dry desert air.The new device is a black, window-sized vertical panel, made from a water-absorbent hydrogel material, enclosed in a glass chamber coated with a cooling layer. The hydrogel resembles black bubble wrap, with small dome-shaped structures that swell when the hydrogel soaks up water vapor. When the captured vapor evaporates, the domes shrink back down in an origami-like transformation. The evaporated vapor then condenses on the the glass, where it can flow down and out through a tube, as clean and drinkable water.

MIT engineers test a passive water harvester in Death Valley, CA. The window-sized setup is made from an origami-inspired hydrogel material (black) that absorbs water from the air, and releases it into tubes where researchers can collect the moisture as pure drinking water.

Credit: Courtesy of the researchers; MIT News

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The system runs entirely on its own, without a power source, unlike other designs that require batteries, solar panels, or electricity from the grid. The team ran the device for over a week in Death Valley, California — the driest region in North America. Even in very low-humidity conditions, the device squeezed drinking water from the air at rates of up to 160 milliliters (about two-thirds of a cup) per day.The team estimates that multiple vertical panels, set up in a small array, could passively supply a household with drinking water, even in arid desert environments. What’s more, the system’s water production should increase with humidity, supplying drinking water in temperate and tropical climates.“We have built a meter-scale device that we hope to deploy in resource-limited regions, where even a solar cell is not very accessible,” says Xuanhe Zhao, the Uncas and Helen Whitaker Professor of Mechanical Engineering and Civil and Environmental Engineering at MIT. “It’s a test of feasibility in scaling up this water harvesting technology. Now people can build it even larger, or make it into parallel panels, to supply drinking water to people and achieve real impact.”Zhao and his colleagues present the details of the new water harvesting design in a paper appearing today in the journal Nature Water. The study’s lead author is former MIT postdoc “Will” Chang Liu, who is currently an assistant professor at the National University of Singapore (NUS). MIT co-authors include Xiao-Yun Yan, Shucong Li, and Bolei Deng, along with collaborators from multiple other institutions.Carrying capacityHydrogels are soft, porous materials that are made mainly from water and a microscopic network of interconnecting polymer fibers. Zhao’s group at MIT has primarily explored the use of hydrogels in biomedical applications, including adhesive coatings for medical implants, soft and flexible electrodes, and noninvasive imaging stickers.“Through our work with soft materials, one property we know very well is the way hydrogel is very good at absorbing water from air,” Zhao says.Researchers are exploring a number of ways to harvest water vapor for drinking water. Among the most efficient so far are devices made from metal-organic frameworks, or MOFs — ultra-porous materials that have also been shown to capture water from dry desert air. But the MOFs do not swell or stretch when absorbing water, and are limited in vapor-carrying capacity.Water from airThe group’s new hydrogel-based water harvester addresses another key problem in similar designs. Other groups have designed water harvesters out of micro- or nano-porous hydrogels. But the water produced from these designs can be salty, requiring additional filtering. Salt is a naturally absorbent material, and researchers embed salts — typically, lithium chloride — in hydrogel to increase the material’s water absorption. The drawback, however, is that this salt can leak out with the water when it is eventually collected.The team’s new design significantly limits salt leakage. Within the hydrogel itself, they included an extra ingredient: glycerol, a liquid compound that naturally stabilizes salt, keeping it within the gel rather than letting it crystallize and leak out with the water. The hydrogel itself has a microstructure that lacks nanoscale pores, which further prevents salt from escaping the material. The salt levels in the water they collected were below the standard threshold for safe drinking water, and significantly below the levels produced by many other hydrogel-based designs.In addition to tuning the hydrogel’s composition, the researchers made improvements to its form. Rather than keeping the gel as a flat sheet, they molded it into a pattern of small domes resembling bubble wrap, that act to increase the gel’s surface area, along with the amount of water vapor it can absorb.The researchers fabricated a half-square-meter of hydrogel and encased the material in a window-like glass chamber. They coated the exterior of the chamber with a special polymer film, which helps to cool the glass and stimulates any water vapor in the hydrogel to evaporate and condense onto the glass. They installed a simple tubing system to collect the water as it flows down the glass.In November 2023, the team traveled to Death Valley, California, and set up the device as a vertical panel. Over seven days, they took measurements as the hydrogel absorbed water vapor during the night (the time of day when water vapor in the desert is highest). In the daytime, with help from the sun, the harvested water evaporated out from the hydrogel and condensed onto the glass.Over this period, the device worked across a range of humidities, from 21 to 88 percent, and produced between 57 and 161.5 milliliters of drinking water per day. Even in the driest conditions, the device harvested more water than other passive and some actively powered designs.“This is just a proof-of-concept design, and there are a lot of things we can optimize,” Liu says. “For instance, we could have a multipanel design. And we’re working on a next generation of the material to further improve its intrinsic properties.”“We imagine that you could one day deploy an array of these panels, and the footprint is very small because they are all vertical,” says Zhao, who has plans to further test the panels in many resource-limited regions. “Then you could have many panels together, collecting water all the time, at household scale.”This work was supported, in part, by the MIT J-WAFS Water and Food Seed Grant, the MIT-Chinese University of Hong Kong collaborative research program, and the UM6P-MIT collaborative research program. More

“Close your eyes and imagine we are on the same team. Same arena. Same jersey. And the game is on the line,” Jaylen Brown, the 2024 NBA Finals MVP for the Boston Celtics, said to a packed room of about 200 people at the recent Day of Climate event at the MIT Museum.“Now think about this: We aren’t playing for ourselves; we are playing for the next generation,” Brown added, encouraging attendees to take climate action. The inaugural Day of Climate event brought together local learners, educators, community leaders, and the MIT community. Featuring project showcases, panels, and a speaker series, the event sparked hands-on learning and inspired climate action across all ages.The event marked the celebration of the first year of a larger initiative by the same name. Led by the pK-12 team at MIT Open Learning, Day of Climate has brought together learners and educators by offering free, hands-on curriculum lessons and activities designed to introduce learners to climate change, teach how it shapes their lives, and consider its effects on humanity. Cynthia Breazeal, dean of digital learning at MIT Open Learning, notes the breadth of engagement across MIT that made the event, and the larger initiative, possible with contributions from more than 10 different MIT departments, labs, centers, and initiatives. “MIT is passionate about K-12 education,” she says. “It was truly inspiring to witness how our entire community came together to demonstrate the power of collaboration and advocacy in driving meaningful change.”From education to action The event kicked off with a showcase, where the Day of Climate grantees and learners invited attendees to learn about their projects and meaningfully engage with lessons and activities. Aranya Karighattam, a local high school senior, adapted the curriculum Urban Heat Islands — developed by Lelia Hampton, a PhD student in electrical engineering and computer science at MIT, and Chris Rabe, program director at the MIT Environmental Solution Initiative — sharing how this phenomenon affects the Boston metropolitan area. 

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Day of Climate inspires young learners to take actionVideo: MIT Open Learning

Karighattam discussed what could be done to shield local communities from urban heat islands. They suggested doubling the tree cover in areas with the lowest quartile tree coverage as one mitigating strategy, but noted that even small steps, like building a garden and raising awareness for this issue, can help.Day of Climate echoed a consistent call to action, urging attendees to meaningfully engage in both education and action. Brown, who is an MIT Media Lab Director’s Fellow, spoke about how education and collective action will pave the way to tackle big societal challenges. “We need to invest in sustainability communities,” he said. “We need to invest in clean technology, and we need to invest in education that fosters environmental stewardship.”Part of MIT’s broader sustainability efforts, including The Climate Project, the event reflected a commitment to building a resilient and sustainable future for all. Influenced by the Climate Action Through Education (CATE), Day of Climate panelist Sophie Shen shared how climate education inspired her civic life. “Learning about climate change has inspired me to take action on a wider systemic level,” she said.Shen, a senior at Arlington High School and local elected official, emphasized how engagement and action looks different for everyone. “There are so many ways to get involved,” she said. “That could be starting a community garden — those can be great community hubs and learning spaces — or it could include advocating to your local or state governments.”Becoming a catalyst for change The larger Day of Climate initiative encourages young people to understand the interdisciplinary nature of climate change and consider how the changing climate impacts many aspects of life. With curriculum available for learners from ages 4 to 18, these free activities range from Climate Change Charades — where learners act out words like “deforestation” and “recycling” — to Climate Change Happens Below Water, where learners use sensors to analyze water quality data like pH and solubility.Many of the speakers at the event shared personal anecdotes from their childhood about how climate education, both in and out of the classroom, has changed the trajectory of their lives. Addaline Jorroff, deputy climate chief and director of mitigation and community resilience in the Office of Climate Resilience and Innovation for the Commonwealth of Massachusetts, explained how resources from MIT were instrumental in her education as a middle and high schooler, while Jaylen Brown told how his grandmother helped him see the importance of taking care of the planet, through recycling and picking up trash together, when he was young.Claudia Urrea, director of the pK-12 team at Open Learning and director of Day of Climate, emphasizes how providing opportunities at schools — through new curriculum, classroom resources and mentorship — are crucial, but providing other educational opportunities also matter: in particular, opportunities that support learners in becoming strong leaders.“I strongly believe that this event not only inspired young learners to take meaningful action, both large and small, towards a better future, but also motivated all the stakeholders to continue to create opportunities for these young learners to emerge as future leaders,” Urrea says.The team plans to hold the Day of Climate event annually, bringing together young people, educators, and the MIT community. Urrea hopes the event will act as a catalyst for change — for everyone.“We hope Day of Climate serves as the opportunity for everyone to recognize the interconnectedness of our actions,” Urrea says. “Understanding this larger system is crucial for addressing current and future challenges, ultimately making the world a better place for all.”The Day of Climate event was hosted by the Day of Climate team in collaboration with MIT Climate Action Through Education (CATE) and Earth Day Boston. More

The accumulation of microplastics in the environment, and within our bodies, is an increasingly worrisome issue. But predicting where these ubiquitous particles will accumulate, and therefore where remediation efforts should be focused, has been difficult because of the many factors that contribute to their dispersal and deposition.New research from MIT shows that one key factor in determining where microparticles are likely to build up has to do with the presence of biofilms. These thin, sticky biopolymer layers are shed by microorganisms and can accumulate on surfaces, including along sandy riverbeds or seashores. The study found that, all other conditions being equal, microparticles are less likely to accumulate in sediment infused with biofilms, because if they land there, they are more likely to be resuspended by flowing water and carried away.The open-access findings appear in the journal Geophysical Research Letters, in a paper by MIT postdoc Hyoungchul Park and professor of civil and environmental engineering Heidi Nepf. “Microplastics are definitely in the news a lot,” Nepf says, “and we don’t fully understand where the hotspots of accumulation are likely to be. This work gives a little bit of guidance” on some of the factors that can cause these particles, and small particles in general, to accumulate in certain locations.Most experiments looking at the ways microparticles are transported and deposited have been conducted over bare sand, Park says. “But in nature, there are a lot of microorganisms, such as bacteria, fungi, and algae, and when they adhere to the stream bed they generate some sticky things.” These substances are known as extracellular polymeric substances, or EPS, and they “can significantly affect the channel bed characteristics,” he says. The new research focused on determining exactly how these substances affected the transport of microparticles, including microplastics.The research involved a flow tank with a bottom lined with fine sand, and sometimes with vertical plastic tubes simulating the presence of mangrove roots. In some experiments the bed consisted of pure sand, and in others the sand was mixed with a biological material to simulate the natural biofilms found in many riverbed and seashore environments.Water mixed with tiny plastic particles was pumped through the tank for three hours, and then the bed surface was photographed under ultraviolet light that caused the plastic particles to fluoresce, allowing a quantitative measurement of their concentration.The results revealed two different phenomena that affected how much of the plastic accumulated on the different surfaces. Immediately around the rods that stood in for above-ground roots, turbulence prevented particle deposition. In addition, as the amount of simulated biofilms in the sediment bed increased, the accumulation of particles also decreased.Nepf and Park concluded that the biofilms filled up the spaces between the sand grains, leaving less room for the microparticles to fit in. The particles were more exposed because they penetrated less deeply in between the sand grains, and as a result they were much more easily resuspended and carried away by the flowing water.“These biological films fill the pore spaces between the sediment grains,” Park explains, “and that makes the deposited particles — the particles that land on the bed — more exposed to the forces generated by the flow, which makes it easier for them to be resuspended. What we found was that in a channel with the same flow conditions and the same vegetation and the same sand bed, if one is without EPS and one is with EPS, then the one without EPS has a much higher deposition rate than the one with EPS.”Nepf adds: “The biofilm is blocking the plastics from accumulating in the bed because they can’t go deep into the bed. They just stay right on the surface, and then they get picked up and moved elsewhere. So, if I spilled a large amount of microplastic in two rivers, and one had a sandy or gravel bottom, and one was muddier with more biofilm, I would expect more of the microplastics to be retained in the sandy or gravelly river.”All of this is complicated by other factors, such as the turbulence of the water or the roughness of the bottom surface, she says. But it provides a “nice lens” to provide some suggestions for people who are trying to study the impacts of microplastics in the field. “They’re trying to determine what kinds of habitats these plastics are in, and this gives a framework for how you might categorize those habitats,” she says. “It gives guidance to where you should go to find more plastics versus less.”As an example, Park suggests, in mangrove ecosystems, microplastics may preferentially accumulate in the outer edges, which tend to be sandy, while the interior zones have sediment with more biofilm. Thus, this work suggests “the sandy outer regions may be potential hotspots for microplastic accumulation,” he says, and can make this a priority zone for monitoring and protection.“This is a highly relevant finding,” says Isabella Schalko, a research scientist at ETH Zurich, who was not associated with this research. “It suggests that restoration measures such as re-vegetation or promoting biofilm growth could help mitigate microplastic accumulation in aquatic systems. It highlights the powerful role of biological and physical features in shaping particle transport processes.”The work was supported by Shell International Exploration and Production through the MIT Energy Initiative. More