Israeli Scientists Develop New System To Harvest Drinking Water From Air

Posted: Jul 27 2016, 4:19am CDT | by , in News | Latest Science News


Israeli Scientists Develop New System to Harvest Drinking Water from Air
An innovative atmospheric moisture harvesting system is proposed, where water vapor is separated from the air prior to cooling and condensation. The system was studied using a model that simulates its three interconnected cycles (air, desiccant, and water) over a range of ambient conditions, and optimal configurations are reported for different operation conditions. Credit: Ben Gido, Eran Friedler, and David M. Broday

Scientists at the Israel Institute of Technology in Haifa have proposed an innovative system for harvesting safe drinking water from air.

Capturing atmospheric moisture is not a new invention in itself because atmospheric water generators for commercial and domestic use already exist. But the new device requires less energy to produce high-quality water from air compared to existing systems, according to the report in American Chemical Society's journal "Environmental Science & Technology."

Atmosphere contains water vapor in amounts comparable to all the surface and underground water on the planet. But current machines that collect water from the atmospheric reservoir have major limitations. They use electrical refrigeration to cool the air and condense the vapor and that consumes a lot of energy.

The new system designed by Israeli scientists uses a liquid desiccant to first separate the water vapor from air and then cool only the vapor. Their calculations show that this approach would result in 20 to 65 per cent energy savings over the standard system.

"We show that the liquid desiccant separation (LDS) stage that is integrated into atmospheric moisture harvesting (AMH) systems can work under a wide range of environmental conditions using low grade or solar heating as a supplementary energy source, and that the performance of the combined system is superior," the report says.

Desalination of seawater by reverse osmosis is also a potential source of fresh water, but it is not applicable in countries that do not have access to the sea. Besides, desalination requires large capital investments in piping and pumping infrastructure and in its operation and maintenance. "Atmospheric moisture is accessible essentially everywhere," says the report.

The atmosphere contains about 13,000 cubic kilometers of freshwater, 98 per cent of it in the form of water vapor, says the report. The vapor must be condensed to liquid water. The existing atmospheric moisture harvesting (AMH) systems, where standard electrical compression-expansion refrigeration unit is used, can save significant energy by first separating the vapor from the bulk air before it enters the condenser, such that only the vapor is cooled rather than the entire air bulk.

In the new design, separation of water vapor from the air is achieved by using a liquid desiccant. The water vapor absorbed by the desiccant can be liberated using low-grade or solar heat.

The liquid-desiccant vapor separation (LDS) subsystem was designed to operate continuously in a closed-cycle, says the report. "The product of this subsystem is pure water vapor, which is then condensed by a standard refrigeration system without the burden of cooling the air."

In general, the combined LDS-AMH system is expected to save up to 65 per cent of the energy expenses of water production relative to off-the-shelf direct-cooling AMH systems, the scientists claim. "Scaling up the LDS system to produce larger amounts of freshwater is possible simply by installing additional absorbing units around a single desorber-condenser core."

Another important advantage, according to the report, is that the water coming out of the LDS-AMH system will be free of airborne bacteria since "the coil of the condenser does not come into contact with the ambient air but only with pure vapor that has been liberated from the desiccant solution."

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