10 gallons per hour from the air from a backpack water harvester in the desert?

via Wikimedia Commons

For thousands of years, people in the Middle East and South America have extracted water from the air to help sustain their populations. Drawing inspiration from those examples, researchers are now developing a lightweight, battery-powered freshwater harvester that could someday take as much as 10 gallons per hour from the air, even in arid locations.

They say their nanofiber-based method could help address modern water shortages due to climate change, industrial pollution, droughts and groundwater depletion.

“I was visiting China, which has a freshwater scarcity problem. There’s investment in wastewater treatment, but I thought that effort alone was inadequate,” Shing-Chung (Josh) Wong, Ph.D., says. Instead of relying on treated wastewater, Wong thought it might be more prudent to develop a new type of water harvester that could take advantage of the abundant water particles in the atmosphere.

Harvesting water from the air has a long history. Thousands of years ago, the Incas of the Andean region collected dew and channeled it into cisterns. More recently, some research groups have been developing massive mist and fog catchers in the Andean mountains and in Africa.

To miniaturize water generation and improve the efficiency, Wong and his students at the University of Akron turned to electrospun polymers, a material they had already worked with for more than a decade. Electrospinning uses electrical forces to produce polymer fibers ranging from tens of nanometers up to 1 micrometer — an ideal size to condense and squeeze water droplets out of the air. These nanoscale fiber polymers offer an incredibly high surface-area-to-volume ratio, much larger than that provided by the typical structures and membranes used in water distillers.

By experimenting with different combinations of polymers that were hydrophilic — which attracts water — and hydrophobic — which discharges water, the group concluded that a water harvesting system could indeed be fabricated using nanofiber technology. Wong’s group determined that their polymer membrane could harvest 744 mg/cm2/h, which is 91 percent higher than similarly designed membranes without these nanofibers.

Unlike existing methods, Wong’s harvester could work in arid desert environments because of the membrane’s high surface-area-to-volume ratio. It also would have a minimal energy requirement. “We could confidently say that, with recent advances in lithium-ion batteries, we could eventually develop a smaller, backpack-sized device,” he says.

What’s more, Wong’s nanofiber design simultaneously grabs water and filters it. The electrospun fiber network can act as an anti-fouling surface, sloughing off microbes that could collect on the harvester’s surface. So the water would be “clear and free of pollutants” and immediately drinkable once it’s collected, he says.

Next, Wong hopes to obtain additional funding to build a prototype of the freshwater harvester. He anticipates that, once his team is able to produce the prototype, it should be inexpensive to manufacture.

This research was presented at a meeting of the American Chemical Society

Learn more: Portable freshwater harvester could draw up to 10 gallons per hour from the air

 

 

The Latest on: Water harvester

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The Latest on: Water harvester
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Fog “harps” could collect more than three-times the amount of clean water from fog

To test the fog harp’s design, researchers constructed small-scale models of vertical wire arrays that could be placed inside an environmental chamber with artificial fog. The team discovered that water collection efficiency continued to increase with smaller and smaller wires.

Fog harvesting may look like whimsical work.

After all, installing giant nets along hillsides and mountaintops to catch water out of thin air sounds more like folly than science. However, the practice has become an important avenue to clean water for many who live in arid and semi-arid climates around the world.

A passive, durable, and effective method of water collection, fog harvesting consists of catching the microscopic droplets of water suspended in the wind that make up fog. Fog harvesting is possible – and has gained traction over the last several decades – in areas of Africa, South America, Asia, the Middle East, and even California. As illustrated by recent headlines of South Africa’s countdown to “Day Zero,” or the day the water taps are expected to run dry, water scarcity continues to be a growing problem across the globe. Leading researchers now estimate that two-thirds of the world’s population already live under conditions of severe water scarcity at least one month of the year.

Fog harvesting could help alleviate that shortage, and now an interdisciplinary research team at Virginia Tech has improved the traditional design of fog nets to increase their collection capacity by threefold.

Published in ACS Applied Materials & Interfaces and partially funded by the Virginia Tech Institute for Creativity, Arts, and Technology, the team’s research demonstrates how a vertical array of parallel wires may change the forecast for fog harvesters. In a design the researchers have dubbed the “fog harp,” these vertical wires shed tiny water droplets faster and more efficiently than the traditional mesh netting used in fog nets today.

“From a design point of view, I’ve always found it somewhat magical that you can essentially use something that looks like screen door mesh to translate fog into drinking water,” said Brook Kennedy, associate professor of industrial design in the College of Architecture and Urban Studies and one of the study’s co-authors. “But these parallel wire arrays are really the fog harp’s special ingredient.”

Fog nets have been in use since the 1980s and can yield clean water in any area that experiences frequent, moving fog. As wind moves the fog’s microscopic water droplets through the nets, some get caught on the net’s suspended wires. These droplets gather and merge until they have enough weight to travel down the nets and settle into collection troughs below. In some of the largest fog harvesting projects, these nets collect an average of 6,000 liters of water each day.

However, the traditional mesh design of fog nets has long posed a dual constraint problem for scientists and engineers. If the holes in the mesh are too large, water droplets pass through without catching on the net’s wires. If the mesh is too fine, the nets catch more water, but the water droplets clog up the mesh without running down into the trough and wind no longer moves through the nets.

Thus, fog nets aim for a middle ground, a Goldilocks zone of fog harvesting: mesh that’s not too big and not too small. This compromise means nets can avoid clogging, but they’re not catching as much water as they could be.

“It’s an efficiency problem and the motivation for our research,” said Jonathan Boreyko, assistant professor in the Department of Biomedical Engineering and Mechanics in the College of Engineering. As a co-author of the study, Boreyko consulted on the theory and physical aspects of the fog harp’s design.

“That hidden regime of making the wires smaller but not clogging is what we were trying to accomplish. It would be the best of both worlds,” he said.

Since the water droplets caught in a fog net move downward with gravity, Boreyko hypothesized that removing the horizontal wires of the net would alleviate some of the clogging. Meanwhile, Kennedy, who specializes in biomimetic design, found his inspiration for the fog harp in nature.

“On average, coastal redwoods rely on fog drip for about one-third of their water intake,” said Kennedy. “These sequoia trees that live along the California coast have evolved over long periods of time to take advantage of that foggy climate. Their needles, like those of a traditional pine tree, are organized in a type of linear array. You don’t see cross meshes.”

Mark Anderson, a study co-author and then-undergraduate student in the Department of Mechanical Engineering, built several scale models of the fog harp with varying sizes of wires. Weiwei Shi, a doctoral student in the engineering mechanics doctoral program as well as the study’s lead author, tested the small prototypes in an environmental chamber and developed a theoretical model of the experiment.

“We found that the smaller the wires, the more efficient the water collection was,” said Boreyko. “These vertical arrays kept catching more and more fog, but the clogging never happened.”

The team has already constructed a larger prototype of the fog harp – a vertical array of 700 wires that measures 3 feet by 3 feet – in an effort led by Kennedy with assistance from Josh Tulkoff, study co-author and a then-undergraduate student in the industrial design program. They plan to test the prototype on nearby Kentland Farm.

Through its unique combination of science and design, the researchers hope the fog harp will one day make a big impact where it’s needed most – in the bottom of the water bucket.

Learn more: Harvesting water from fog with harps

 

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A water harvester that pulls all the water a household needs out of the air – even in dry climates

The water harvester, built at MIT, uses MOFs synthesized at Berkeley to suck water from dry air. The harvester uses sunlight to heat the MOF, driving off the water vapor and condensing it for use. MIT photo by Hyunho Kim.

Imagine a future in which every home has an appliance that pulls all the water the household needs out of the air, even in dry or desert climates, using only the power of the sun.

That future may be around the corner, with the demonstration this week of a water harvester that uses only ambient sunlight to pull liters of water out of the air each day in conditions as low as 20 percent humidity, a level common in arid areas.

Omar Yaghi explains how to make a MOF and their tremendous ability to absorb gases and liquids, including water directly from low-humidity air. A MOF he synthesized was used by MIT engineers to construct a water harvester that sucks water from dry air and condenses it for drinking. Video by Roxanne Makasdjian and Stephen McNally, UC Berkeley. Harvester photos courtesy of MIT.

The solar-powered harvester, reported in the journal Science, was constructed at the Massachusetts Institute of Technology using a special material — a metal-organic framework, or MOF — produced at the University of California, Berkeley.

“This is a major breakthrough in the long-standing challenge of harvesting water from the air at low humidity,” said Omar Yaghi, one of two senior authors of the paper, who holds the James and Neeltje Tretter chair in chemistry at UC Berkeley and is a faculty scientist at Lawrence Berkeley National Laboratory. “There is no other way to do that right now, except by using extra energy. Your electric dehumidifier at home ‘produces’ very expensive water.”

The prototype, under conditions of 20-30 percent humidity, was able to pull 2.8 liters (3 quarts) of water from the air over a 12-hour period, using one kilogram (2.2 pounds) of MOF. Rooftop tests at MIT confirmed that the device works in real-world conditions.

“One vision for the future is to have water off-grid, where you have a device at home running on ambient solar for delivering water that satisfies the needs of a household,” said Yaghi, who is the founding director of the Berkeley Global Science Institute, a co-director of the Kavli Energy NanoSciences Institute and the California Research Alliance by BASF. “To me, that will be made possible because of this experiment. I call it personalized water.”

Tinker toys

Yaghi invented metal-organic frameworks more than 20 years ago, combining metals like magnesium or aluminum with organic molecules in a tinker-toy arrangement to create rigid, porous structures ideal for storing gases and liquids. Since then, more than 20,000 different MOFs have been created by researchers worldwide. Some hold chemicals such as hydrogen or methane: the chemical company BASF is testing one of Yaghi’s MOFs in natural gas-fueled trucks, since MOF-filled tanks hold three times the methane that can be pumped under pressure into an empty tank.

diagram of metal-organic framework

A schematic of a metal-organic framework. The lines in the models are organic linkers, and the intersections are metal ions. These are the building blocks that Yaghi stitches together into crystalline sponges using what he calls reticular chemistry. The yellow balls represent the porous spaces that can be filled with gas or liquid. The background image shows individual MOF crystals, which are packed into the water harvester. UC Berkeley, Berkeley Lab image.

Other MOFs are able to capture carbon dioxide from flue gases, catalyze the reaction of adsorbed chemicals or separate petrochemicals in processing plants.

In 2014, Yaghi and his UC Berkeley team synthesized a MOF – a combination of zirconium metal and adipic acid – that binds water vapor, and he suggested to Evelyn Wang, a mechanical engineer at MIT, that they join forces to turn the MOF into a water-collecting system.

The system Wang and her students designed consisted of more than two pounds of dust-sized MOF crystals compressed between a solar absorber and a condenser plate, placed inside a chamber open to the air. As ambient air diffuses through the porous MOF, water molecules preferentially attach to the interior surfaces. X-ray diffraction studies have shown that the water vapor molecules often gather in groups of eight to form cubes.

Sunlight entering through a window heats up the MOF and drives the bound water toward the condenser, which is at the temperature of the outside air. The vapor condenses as liquid water and drips into a collector.

“This work offers a new way to harvest water from air that does not require high relative humidity conditions and is much more energy efficient than other existing technologies,” Wang said.

water harvester

The harvester sitting atop a roof at MIT. The MOF is just below the glass plate on top, which lets sunlight in to heat the MOF and drive off the absorbed water. The yellow and red condenser sitting at the bottom is covered with water droplets. MIT photo by Hyunho Kim.

This proof of concept harvester leaves much room for improvement, Yaghi said. The current MOF can absorb only 20 percent of its weight in water, but other MOF materials could possibly absorb 40 percent or more. The material can also be tweaked to be more effective at higher or lower humidity levels.

“It’s not just that we made a passive device that sits there collecting water; we have now laid both the experimental and theoretical foundations so that we can screen other MOFs, thousands of which could be made, to find even better materials,” he said. “There is a lot of potential for scaling up the amount of water that is being harvested. It is just a matter of further engineering now.”

Yaghi and his team are at work improving their MOFs, while Wang continues to improve the harvesting system to produce more water.

“To have water running all the time, you could design a system that absorbs the humidity during the night and evolves it during the day,” he said. “Or design the solar collector to allow for this at a much faster rate, where more air is pushed in. We wanted to demonstrate that if you are cut off somewhere in the desert, you could survive because of this device. A person needs about a Coke can of water per day. That is something one could collect in less than an hour with this system.”

Learn more: Device pulls water from dry air, powered only by the sun

 

 

 

The Latest on: Water harvester

via Google News

 

The Latest on: Water harvester
  • Bengaluru to get enough water this summer
    on January 11, 2019 at 7:11 pm

    “People should start using less water and not waste it unnecessarily. Rain water harvesting has not been implemented effectively. If it had been done, we would not have been in this position,’’ offici... […]

  • Designing your 2019 Water Wise landscape
    on January 10, 2019 at 10:35 am

    Print out an aerial picture If available, use your property plat drawing to identify total area Walk your yard noting sun exposure, established plants, potential water harvesting areas, etc. Albuquerq... […]

  • Wild fish harvesters rally to fight US aquaculture push in new Congress
    on January 9, 2019 at 10:25 am

    A group of about 140 mostly small-scale harvesters and their regional trade groups have ... to chair the committee’s panel on water, power and oceans. Oppenheim plans on talking to both lawmakers abou... […]

  • Harvester gathers dust three years later as weed spreads
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    The unique water harvesting attributes of this beetle’s wings was first described about ten years ago. This technology even inspired a “self-filling” water bottle. Challenges persist if we hope to cap... […]

  • Three people caught harvesting polluted oysters in Terrebonne
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    The oysters were returned to the water. The penalty for taking oysters from a polluted area is a fine of up to $950 and up to 120 days in jail. The suspects could also have their oyster harvester lice... […]

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