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It is estimated that around four billion people on the globe suffer from water scarcity. Distribution and production of fresh water and the control over water sources are potential cause for conflicts. Therefore, researchers are investigating new ways of freshwater production and the improvement of existing techniques.
Potable water is also essential to maintain health and sustain military operations, From a medical and physiological perspective, lack of adequate water results in dehydration, which increases risk of serious heat illness and performance impairment, especially during prolonged exposure to wet bulb globe temperatures above 30°C. The Defense Advanced Research Projects Agency (DARPA) has initiated a program providing deployed units technology to capture potable water from the air in quantities sufficient to meet daily needs. The extraction of water from air is a promising way to supply freshwater, especially in remote, arid regions.
Water is a critical resource for survival. Many remote locations have limited or polluted water supplies. Existing methods of water purification, such as desalination, require large pieces of equipment and are energy-intensive. Further, water is cumbersome to transport, presenting a logistical and economic challenge for supplying water to distant areas.
Providing potable drinking water to deployed troops operating in low resource or contested environments is no simple undertaking. Carrying and transporting water is a major logistical burden. Provision of adequate water is a challenge on the modern battlefield, especially in mountainous terrains and/or when roads are poorly maintained or nonexistent. In such cases, water is either carried on foot or air-dropped, which requires tremendous manpower, vehicle space, and fuel consumption, making water transport one of the largest military logistical supply burdens.
Logistics teams face great risk delivering water and often incur what would otherwise be preventable casualties. DARPA’s new Atmospheric Water Extraction (AWE) program sets out to sharply reduce that risk by giving deployed units the technology to capture potable water on the spot from the air in quantities sufficient to meet daily needs of the warfighter, even in extremely dry areas of the world.
“The demand for drinking water is a constant across all Department of Defense missions, and the risk, cost, and complexity that go into meeting that demand can quickly become force limiting factors,” said Seth Cohen, the AWE program manager. “Right now, the military relies on purification of regional fresh and saline water sources, or transported bottled water, neither of which are optimal for mobile forces that operate with a small footprint. DARPA is turning to atmospheric water extraction as a potential solution that offers maximal operational flexibility with minimal risk.”
There are two general options for water harvesting from air:
1) Ambient air can be cooled below its dew point and the condensed liquid water can be collected. Large volumes of air and low temperatures at the condenser are required, especially in regions of low relative humidity (r.h.). The cooling of the heat sink for the condensation can be energy consumptive, since a difference in temperature between the condensation unit and the ambience has to be maintained. Additionally, the heat of condensation of the collected water has to be discharged.
2) Humidity can be adsorbed or absorbed (taken up) by desiccant materials, and in a second step desorbed at elevated temperatures followed by condensation of the hot water vapor at ambient conditions. Usually water is taken up during the colder nighttime when the relative humidity is higher and desorbed during daytime. The necessary heat for desorption is ideally provided by solar radiation. The resulting heated water vapor can be brought below its dew point and condensed at ambient temperatures, making an energy expansive auxiliary heat sink redundant. When the ambient air is used as coolant, a sufficient airstream has to be maintained to reject the heat of condensation.
Some of the desiccant materials are zeolites, metal−organic frameworks, or hygroscopic salts. Up untill now, it has been proven difficult to synthesize most of the suitable MOFs on a scale that allows for significant, cost-efficient water production. Apart from water harvesting through adsorption on the surface, it is possible to harvest water through absorption, e.g., hydration of salts.
One of the most promising salts is calcium chloride because of its excellent water sorption properties in combination with a natural and industrial abundance. The salt is able to absorb more than 95% of its own weight in water for the reaction of the anhydrous salt to the hexahydrate. However, hygroscopic salts face the problem of particle agglomeration during hydration, which reduces the gas permeability.
DARPA AWE program
DARPA is open to various approaches, with an emphasis on advanced sorbents that can rapidly extract water from ambient air and release it quickly with minimal energy inputs. These sorbent materials offer potential solutions to the AWE challenge, provided they can be produced at the necessary scale and remain stable over thousands of extraction cycles. In addition to developing new sorbents, AWE researchers will need to engineer systems to optimize their suitability for highly mobile forces by substantially reducing the size, weight, and power requirements compared to existing technologies.
The AWE program has two tracks. Researchers supporting the Expeditionary Track will target deliverables built around the daily potable water requirement for an individual, in a compact, portable form factor. Researchers on the Stabilization Track will develop technology that is transportable on a standard military vehicle and can support a company of up to 150 people.
“If the AWE program succeeds in providing troops with potable water even in arid climates, that gives commanders greater maneuver and decision space and allows operations to run longer,” said Cohen. “Ultimately, the technology could even diminish the motivation for conflicts over resources by providing a new source of drinking water to stressed populations.”
AWE Awards
In Nov 2020, The research business arm of General Electric received a two-year, $14.3M contract to help the Defense Advanced Research Projects Agency develop a fuel-powered device for potable water production. GE Research will create sorbent materials for the first phase of DARPA’s Atmospheric Water Extraction program, which aims to develop systems for extracting water from ambient air during military, stabilization and humanitarian missions, the Department of Defense said Wednesday.
Physical Sciences Inc. (PSI), in collaboration with Cascade Designs Inc. (CDI) and the University of Massachusetts Amherst, has signed a contract with the Defense Advanced Research Projects Agency (DARPA) to develop a new atmospheric water extraction (AWE) device that can capture clean drinking water from air. The developed technology is intended to supply water in remote areas, to forward deployed soldiers, and during emergency situations.
The PSI team aims to overcome these challenges by creating a new class of water capturing materials incorporated into an ultra-lightweight and portable water harvesting system. The centerpiece of the team’s technology is a novel Smart Moisture Absorbing Foam, or a SMAF. The SMAF will capture atmospheric water across a wide variety of environments, and over a range of temperatures and relative humidity. The SMAF also has very high water storage capacity, enabling daily operational cycles and minimizing frequency of user interaction. The key property of the SMAF is that water is released by compression. The material is ‘smart’ because it switches from hydrophilic (‘water loving’) to hydrophobic (‘water rejecting’) as it is compressed – thereby expelling any trapped water.
Typical state of the art water capture materials release water by energy-intensive heating. Releasing water by compression greatly reduces the amount of energy required to power the system, enabling ultimate portability. As a part of the effort, the SMAF material will be incorporated into several prototype devices. The final device will be easily carried by an individual as a primary water supply. The team aims to create a lightweight, compact, durable and easy-to-operate water harvesting system that fits within the stringent DARPA size weight and power targets.
The goal of this new research is a portable and robust system capable of extracting potable drinking water from ambient air. To ensure portability, the system is designed to fit within a strict size, weight and power envelope. Such technology has game-changing implications for both military and humanitarian purposes.
The agency looks to harvest water from desert air through the AWE program and expects Phase 1 of the program to conclude in November 2022. Seventy-seven percent of contract work will take place in Niskayuna, New York, and the rest in California, Illinois and Alabama.
