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A team of architects and environmental engineers has proposed covering swaths of the Sahara with vast “salt water greenhouses” powered by solar power arrays, in a plan they call the Sahara Forest Project. Charlie Paton, inventor of the salt water greenhouse, says the combined technologies could transform patches of the desert from arid wastelands into lush expanses that produce a bounty of fruits and vegetables for local people.
The plan is no doubt ambitious and unproved at this scale, but Paton says he has built demonstration greenhouses on the Spanish island Tenerife, as well as in Abu Dhabi and Oman; he says there is further interest in funding demonstration projects from across the Middle East, including UAE, Oman, Bahrain, Qatar and Kuwait. The cost is not as astronomical as one would think, and is estimated at approximately $118 million for a 20 hectare [50 acre] site of greenhouses and a 10MW concentrated solar power farm [Red Herring]. Paton is working with Exploration Architecture, a company that worked on the world’s largest greenhouse in England’s Eden Project.
The greenhouses work by using the solar farm to power seawater evaporators and then pump the damp, cool air through the greenhouse. This reduces the temperature by about 15C compared to that outside. At the other end of the greenhouse from the evaporators, the water vapour is condensed. Some of this fresh water is used to water the crops, while the rest can be used for the essential task of cleaning the solar mirrors. “So we’ve got conditions in the greenhouse of high humidity and lower temperature,” said Paton. “The crops sitting in this slightly steamy, humid condition can grow fantastically well” [The Guardian].
The project would use a concentrated solar power (CSP) system, in which huge mirrors focus the sun’s rays onto water heaters, which produces steam to power turbines. As the dreamers envision it, the Sahara Forest Project would be established near the north coast of Africa. The scheme has been designed as a ‘hedge’ of greenhouses providing a windbreak and shelter for the outdoor planting. CSP arrays will be placed at intervals along the greenhouse ‘hedge’. The greenhouses produce five time more fresh water than needed for the plants inside. This surplus will be used to irrigate the planted orchards and the Jatrophra [sic—the correct name is “Jatropha”] crop, which can be turned into bio-fuel for transportation and other needs [Treehugger].
Image: Exploration Architecture
Related Post: A Solar Power Plant in the Sahara Could Power All of Europe
Source: http://blogs.discovermagazine.com/80beats/2008/09/02/architects-propose-fantastic-greenhouses-across-the-sahara/
Is Canada self-sufficient in food production?
One remarkable forest is busy purifying the planet.
by Dava Sobel
From the January 2009 issue, published online December 26, 2008
Agronomist Cristina Negri Agronomist Cristina Negri collects poplar samples to measure the pollutants sucked from the earth.
George Joch/Argonne National Laboratory
Argonne, Illinois—A legacy of the Argonne National Laboratory’s early foray into atomic energy lies buried here on its campus, about 25 miles southwest of Chicago. Although solid wastes from all sorts of experiments have been sealed in a landfill, certain liquids, mostly chlorinated solvents, still taint the water that runs under the site. The ongoing attempt to remove these contaminants occupies an enormous experimental facility that covers four acres and looks like a forest.
“I like to brag that I have the biggest lab at Argonne,” says agronomist Cristina Negri, indicating an expanse of 900 poplars and willows growing in rows. The trees stand about 30 feet high. More important, their roots extend 30 feet down, where they tap the contaminated aquifer and literally pull pollutants out of the ground.
“The purpose here is not to grow the most beautiful trees,” Negri says as she walks among them. “It’s to make them work.”
Under normal circumstances, tree roots prefer to sip water from sources as close as possible to the surface. But these trees, planted in 1999, don’t have that option. They are impressed laborers, set into plastic-lined pits that force their roots to tunnel deep for drink. The roots lift the contaminated water into the tree trunks, where transport tissues conduct it on up to the branches and leaves. From there, as droplets transpire through leaf pores, the water evaporates and sunlight breaks down the dissolved solvent molecules, rendering them harmless. As Negri explains the process, the smell of poplar seems to excite her like catnip.
Before the willows and poplars took over the job of wastewater management, Argonne was using extraction wells to pump contaminated water to a treatment plant. But the static mechanical pumps could not chase after groundwater that continually changed course through the complex terrain. The natural pump of a willow or poplar, on the other hand, is not only self-sustaining but so water-loving that it will snake down or fan out as far as need be to reach moisture.
Negri’s trees each pump as much as 26 gallons of water per day at their summer peak. She measures the daily flow through the trunks by inserting probes that transmit data to solar-powered recorders mounted on tripods nearby. Periodically, laboratory workers roam the forest to sample bark, small branches, and leaves to assess the trees’ success in pollution extraction.
“That’s the beauty of this site. On a nice day, we just say, ‘OK, let’s go sampling!’ We don’t have to plan for trips or pack dry ice. We just take our collection bottles into the field, and when we’re done we carry them back inside to our other lab.” The glass collecting vials are sealed and either frozen for future study or oven-heated to 90 degrees Centigrade (194° Fahrenheit), hot enough to volatilize the pollutants from the tree tissues. An automated gas chromatography apparatus then extracts a puff of air from each bottle and quantifies the type and concentration of pollutants released.
In summer, trichloroethane levels generally run high (several thousand parts per billion), but in winter, after the leaves fall, the roots stop pumping and the bare branches bear no sign of contamination. Since the trees don’t accumulate any permanent residue of pollution, they can eventually be chopped down and chipped, their remains distributed around other plantings for soil enrichment.
The technical term for this green, and increasingly prevalent, form of environmental cleanup is phytoremediation. At Argonne it will give way, over the next 20 to 30 years, to ecological restoration, as the pollutants are removed and the worker trees replaced by bur oaks and other hardwoods native to the Great Lakes region—trees that grow slowly and draw only a fraction of the water taken up by the hasty, thirsty poplars and willows.
“I’ve turned everybody I know into a willow watcher,” Negri says. “In the spring, willows are the first trees to turn yellow and green and start putting leaves out.”
Worker trees like poplars and willows will one day give way to expanses of native oaks.
A second Argonne experimental forest, in Murdock, Nebraska, is helping the U.S. Department of Agriculture address the mess that it made in corn-belt communities during the 1960s, when storage drums full of grain were routinely fumigated with carbon tetrachloride to control pests. The colorless liquid seeped into the ground and continues even now to foul the local water supply.
When members of the Argonne team arrived at Murdock in 2004 for an initial assessment, they found trace levels of “carbon tet” in the resident vegetation. Their solution, implemented the next year, was to create an instant forest. Most of the 2,000 planted saplings were poplars and willows, the same types that had demonstrated their effectiveness in Illinois. Local varieties, such as green ash and catalpa, were added to the mix to test their cleanup capabilities, along with Nebraska wildflowers for diversity and a wetland to buffer and further beautify the woods. “People would much rather see a forest than a pump.”
By 2007, two years after planting, the exact location of the underground plume of contamination could be mapped from the surface by examining the trees. Even in summer, trees in some areas tested clean while those in others were steadily bringing up carbon tetrachloride. Meanwhile, all the trees seemed to have enjoyed unusually rapid growth thanks to another pollutant in the Murdock soil: nitrate, possibly from fertilizers applied in the surrounding cornfields.
“I chose agriculture when I first went into science because I wanted to be a nature doctor,” Negri says. “I loved the order and neatness of plowed fields. I never realized then how polluting agriculture could be.”
The compatibility of the forest and the fields conjures another poplar dream of combining remediation with energy production. Negri’s colleagues have looked to the poplars as a possible source of ethanol for biofuel. The trees’ need for plentiful water seemed at first to make them a poor choice, since water itself is likely to become scarce. But if the trees can slake their thirst with polluted water, and if they can grow on marginal land ill-suited for crops, then their promise as an alternate energy source grows doubly green.
Source: http://discovermagazine.com/2009/jan/26-worker-trees-clean-contaminated-water
Associated Press
By JANET McCONNAUGHEY , 07.25.09, 09:46 AM EDT
NEW ORLEANS — The Gulf of Mexico’s “dead zone” – where there is too little oxygen in the water for anything to live – is less than half the size predicted earlier this year but also unusually severe, a scientist said Friday.
The hypoxic area forms every year in the Gulf, caused by bacteria feeding on algae blooms from the flow of farming runoff and other nutrients from the Mississippi River and others.
This year’s area covers 3,000 square miles, but is also unusually thick, stretching from the bottom nearly to the surface, according to Nancy Rabalais, a researcher who specializes in the problem for the Louisiana Universities Marine Consortium.
The 3,000 square miles is one of the smallest measurements of the zone since measurements began in 1985, according to a graph in a news release sent from a research vessel in the Gulf. Only those in 1987, 1988 and 2000 were smaller.
Other scientists had predicted that this year’s dead zone would cover about 7,500 to 8,500 square miles.
Possible reasons for the difference include high winds and waves that helped mix more oxygen into some waters, she wrote.
“This was surprisingly small given the forecast to be among the largest ever and the expanse of the dead zone earlier this summer,” she wrote.
Hypoxia occurs when algae blooms, fed by nitrates and phosphates in the water, die and fall to the bottom. At the same time, winds die down, meaning that fresh water coming out of the rivers doesn’t get mixed into the denser salt water below it. Microbes feeding on the dead algae use up oxygen from the bottom up.
Rabalais said that in some areas where the oxygen was lowest, crabs, eels and shrimp – creatures which usually live on the bottom – were seen swimming at the surface.
Other studies indicate that severely low oxygen levels in early July contributed to “jubilees” – forced movement of fish, crabs and shrimp into shallow waters – off Grand Isle, she said.
Rabalais and other researchers are expected on Monday to discuss the hypoxic problem in a telephone news conference with Jane Lubchenco, head of the National Oceanic and Atmospheric Administration.
“We want to raise some of the issues behind it and some of the debate about the changes needed to shrink it,” NOAA spokesman Ben Sherman said Wednesday.
While the Gulf’s dead zone is among the largest, there are more than 250 hypoxic areas in U.S. waters, according to researcher Robert Diaz of Virginia Marine Institute.
Copyright 2009 Associated Press. All rights reserved. This material may not be published broadcast, rewritten, or redistributed
Source: http://www.forbes.com/feeds/ap/2009/07/25/ap6700073.html?partner=alerts
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