Eco Sustainable Village
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Eco Sustainable Village |
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Simple Solution for producing clean drinking water
This plant can be made in under $ 2000 and can produce 1000 gallons daily from salty water. According to the United Nations, more than 1 billion people do not have access to clean drinking water, and 2.2 million die from contaminated water each year. Arsenic, chromium, benzene, bacteria and other contaminants enter drinking water supplies from both natural and human sources. Each nation deals with a different mix of contaminants in its own way. But one thing is certain: the lack of pure water inhibits development around the world. Jim Beckman is an associate professor of chemical and materials engineering at Arizona State University. Several years ago, he got interested in the concept of desalination. Beckman thought that he could do better than reverse osmosis (RO), the current king of desalination and water purification processes. He thought that he could make a difference in a discipline that many colleagues considered dead. For years, the ASU researcher’s ideas were rebuffed. Other chemical engineers ignored his presentations at conferences. They all were totally sold on RO. Beckman persisted. Today, he has a patent, a spinout company, and a device that does more than just desalination. He says that his invention has the potential to bring clean, fresh water to people around the globe. And Beckman did it all by keeping things simple. During the 1950s and 1960s, researchers across the nation worked to develop cost-efficient methods for removing salt from seawater. Reverse osmosis was the best process they discovered. During the RO process, salty water is pumped into a tank containing a fine membrane. The membrane allows water to pass through but not salt and other compounds dissolved in the water. Pressure from the pump forces pure water through the membrane; the water then flows out of the tank. For decades, RO has been the primary method for desalination and water purification. But the process has its drawbacks. Pushing water through the membrane requires significant pressure. Creating the pressure takes energy. Chloride in seawater corrodes metal, so parts must be replaced regularly. Beckman says that RO performs better when contaminant concentrations are low. It also removes some compounds better than others. Reverse osmosis systems frequently include both pre- and post-filters to help remove what the membrane does not. In short, RO works, but it is expensive. Beckman’s idea was to create a unique, inexpensive desalination system. “Keep it simple” became the motto for his laboratory. To avoid corrosion, Beckman built his device largely of plastic. Plastic has the added benefits of being lightweight and inexpensive. Applying pressure and raising temperature both require energy. Beckman designed his device to work at atmospheric pressure and at low temperature. He chose cheap, abundant steam as a heat source. The final device is simple, yet elegant. “We have a unit that costs less than reverse osmosis to buy and almost nothing to operate,” Beckman says. “It’s a nice device for a home. It’s great for third world countries. There’s virtually nothing to break down.” Beckman’s desalination device is based on the simple, natural processes of evaporation and dew formation. During evaporation, liquid water changes into water vapor, a gas. It’s how wet laundry hanging in the sun becomes dry. Most water contains a variety of dissolved chemicals and other materials. When the water evaporates, the other stuff is usually left behind. Think about the salty film on your skin after sweat evaporates. Dew formation is the opposite of evaporation. Water vapor becomes liquid. It’s why you find a film of water on your lawn after a chilly night. Beckman’s device evaporates seawater in one compartment and forms pure dew in another. He calls the technology “dewvaporation.” NEWT Double Helix Tower is the official name of Beckman’s device. But everyone calls it “Dewey.” The Dewey is unimpressive at first glance. It’s a 2-foot by 2-foot by 5-foot white plastic box held together with packing tape, covered with insulation, and attached to a pump and a blower. Salty water goes in the top. At the bottom, clean freshwater flows out one side and much saltier water flows out the other. During demonstrations, Beckman and his research team add green food color to the water so that visitors can see which side is which. Despite its appearance, Beckman’s simple plastic box is a powerhouse. It can ingest seawater with a concentration of 3 percent salt, and spit out water with a salt concentration of nearly zero. Actually, Dewey has processed water with up to 20 percent salt, a concentration RO simply cannot handle. Dewey can also remove arsenic, mercury, ethanol, and every other contaminant the Beckman lab has thrown at it so far. “We haven’t found water we can’t treat,” says Victor Banks, a graduate student in Beckman’s lab. A paper cutter is the most advanced tool used to build a Dewey. The plastic Beckman uses for the device is the same type used to make the political signs that sprout in vacant lots before elections. Other components include cotton and nylon gauze, packing tape, insulating foam, and silicone. Building a Dewey takes two to three weeks, but only because graduate students need sleep and the silicone requires drying time. On an assembly line, the work will go much faster. To date, Deweys built in Beckman’s lab can process 50 to 100 gallons of water per day. He says that larger Deweys are possible by connecting several smaller ones. During spring 2003, four Deweys were put to the test at Salt River Project’s Coronado Generating Station in St. Johns, Ariz. Power plants use water to prevent a variety of machines from overheating. The salty waste water is usually pumped to outdoor evaporating ponds, which become more and more concentrated with salt and other chemicals as the water evaporates. Evaporating ponds can cover large tracts of land around the power plant and can become an environmental hazard. At the Coronado Station, technicians connected the Deweys in series to process waste cooling water with an initial 1.2 percent salt concentration. During a month-long test run, the Deweys processed 213 gallons of water per day. The yield was 200 gallons of pure water and 13 gallons of concentrated salt water. Beckman says this is equivalent to reducing the size of an evaporation pond to less than 10 percent of the acreage normally required. Power generation is only one of many industrial processes that require cooling water. Other industries produce contaminated water as a waste product. Steam and heat are also common waste products. Beckman says that Dewey could clean up water cheaply and efficiently by taking advantage of what industry needs to get rid of anyway. Municipal water systems could also use Dewey to purify water and reduce the number of chemicals added to the water supply. Beckman is working with the Bureau of Reclamation and the City of Phoenix to install a Dewey that can process 10,000 gallons of water per day at a Phoenix water treatment plant. L’Eau is the company Beckman started in an effort to commercialize Dewey. L’Eau means “water” in French. The company plans to sell Deweys to industrial and municipal customers, then re-invest the profits toward making Deweys for people who have no access to clean water. Beckman thinks that Dewey is a great device for remote, undeveloped locations. Dewey itself has no moving parts, nothing to break down. The external pump and blower can be switched out easily. Because of the device’s modular design, the amount of water processed can be changed simply by connecting more units. The military is also intrigued as Dewey is light, compact, easily transported and operated, and if damaged, can be repaired with duct tape. Dewey works the best in the desert for seawater desalination. By including a desiccant heat pump which replaces the need for steam, potable water from the oceans can be made for less than $1 per 1,000 gallons. Areas that would benefit from the desiccant add-on include: Arizona, California, Mexico, North Africa, Australia, and most Middle Eastern countries.
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