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Out Of Thin Air
by Alex Mendelsohn
While lots of folks are talking about generating electrical power from wind turbines and photovoltaic arrays, there's also worldwide concern about a looming global water shortage. There's an abundance of breezes and sunshine, but potable water is a bounded resource in parts of the world, especially in countries where deserts dominate the landscape. That picture is changing, in part thanks to electronics.
Researchers at the Fraunhofer Institute for Interfacial Engineering and Biotechnology in Germany are working on a system that literally pulls drinking water from the air. What's more, the Fraunhofer scientists are doing it using renewable energy, focusing on parts of the world where there are no lakes, rivers, or groundwater.
In these regions there may be sufficient amounts of water stored in the air. In the Negev desert in Israel, for example, the annual average relative humidity is 64%. That means that in every cubic meter of air there's 11.5 ml of water, or more than a third of an ounce.
Humidity To Drink
Working in conjunction with Logos Innovationen, the Fraunhofer scientists are converting airborne humidity into drinking water. "The process is based exclusively on renewable energy sources such as thermal solar collectors and photovoltaic cells," says Siegfried Egner, head of the Institute's research department. "That makes this method completely energy-autonomous."
According to Egner, the technique can even be applied in parts of the world where there is no electrical power generation and/or distribution infrastructure. The system uses hygroscopic brine, a saline solution that absorbs moisture. The brine runs down a tower-shaped unit where it absorbs water from the air. This is then sucked into a vacuum tank. Electrical energy then heats up the brine, which is diluted by the water it has absorbed.
Because of the vacuum, the boiling point of the liquid is lower than it would be under normal atmospheric pressure. If you've ever hiked into the mountains, and tried to boil water to cook, where the air pressure is lower, water boils at a lower temperature, and you can't always fully cook your pasta.
In the hygroscopic brine system, the evaporated non-saline water is condensed and runs down through a completely filled tube in a controlled manner. What's really nifty is that the gravity of this water column continuously produces a vacuum, so a vacuum pump isn't needed. The re-concentrated brine then runs down the tower surface again to absorb more moisture from the air.
Water For Everyone
"The concept is suitable for various sizes of installation," says Egner. He envisions units that can supply water for a single person or for an entire building, and says air moisture absorption and vacuum evaporation prototypes have already been built and tested in the lab. A larger demonstration facility is planned.
In another Fraunhofer Institute experiment an urban infrastructure water-saving vacuum sewerage network is under development. Professor Walter Trosch points out that a third of the total amount of clean water in homes is flushed down toilets. "Water is one of our most valuable resources, and far too precious to waste on transporting fecal matter," he says.
Together with Dr Werner Sternad at Fraunhofer and Dr Harald Hiessl of the Institute's Systems and Innovation Research unit in Karlsruhe, Trosch designed and created what he calls DEUS 21, a decentralized urban infrastructure system. "DEUS is an integrated model that looks at water as a commodity all the way from the faucet to the treatment plant," says Trosch.
 In a DEUS 21 system, rainwater is also collected instead of channeling it away through sewers. This rainwater is separate from wastewater and is treated in a membrane plant. As the membrane's pores are smaller than bacteria and viruses, pathogens are filtered, resulting in germ-free drinking water.
This very soft water flows back into households through a separate supply network, and can be used for showering or for washing dishes or clothes. Wastewater from the households is then collected in a vacuum sewerage system.
The system also ingests shredded kitchen scraps, which sidesteps the need for separate waste collection. The wastewater is transported to hermetically sealed high-performance reactors containing rotation filters. These filters comprise porous ceramic micro-filtration membranes that remove anything larger than 0.2 micron from the wastewater – including bacteria that decompose organic waste.
But, wait. It gets better. Bio-gas that's recovered can be used to generate power and heat. Nitrogen and phosphates are also reclaimed from the wastewater and processed to produce high-quality plant fertilizer. What remains is purified wastewater that meets the quality requirements of the European directive on bathing water quality. Finally, this water can be drained or discharged into any body of water.
Pilot applications in Germany have proven both the economic and ecological benefits. Based on these successes, projects are being planned in Namibia, China, and Romania.
Plants In The Air
Here in the States, a Nevada company called NewGardens is doing something a bit different. It's commercializing and licensing aeroponics, a technique for growing plants in air. NewGardens already grows tomatoes commercially using aeroponics in the Canary Islands, and it's building an aeroponics facility on the campus of the University of Nevada.
Aeroponics promises much lower water and energy inputs per square meter of growing area than hydroponics. "Universities and hobbyists have played with aeroponics," says Bill Sobolewski, NewGardens operations director, "but there haven't been many successful large scale commercial operations.”
Microprocessors Are Key
"The key to success," adds Sobolewski, "is technology: especially the use of electronics and microprocessors." Sobolewski describes how processors control the duration and frequency of mist sprayed on plant roots. The roots hang suspended in air in enclosed chambers, while the rest of the plant grows outside the chamber.
Software and hardware control carbon dioxide quantities, air exchange rates, temperature, humidity, heat, and other variables. Software manages aeroponic cultivation and controls the greenhouse environment in realtime. The company uses a package called Aeroponic Plant Control System for Windows. This graphics package handles realtime data recording, adds password control, remote access and multi-user access, and performs system diagnostics and alarms.
Sobolewski says electricity use is minimal, unless grow lights are used in the evening to bolster growth rates. The real savings, he says, is water. "We use only about 10% of the water of a hydroponics system. The NewGardens system is a closed loop, with little water loss."
NewGardens contends aeroponically grown tomatoes are exceptional in a number of ways. Their flavor is better, given high natural sugar and acid concentration, and they can be grown consistently year-round. They can be grown up to 50% percent faster, too, and are fully organic, without any harmful chemicals or pesticides.
The company now has commercial operations in the Canary Islands, and is pioneering the technique in the United States. Sobolewski says NewGardens is also ready to license its technology – out of thin air!
Your comments are welcome. Please write me at amm at en-genius dot net, or post your thoughts and observations on our blog.
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