Posts Tagged ‘water filters’
Electrified Cotton Filter Soaked in Nanotech Cheaply and Quickly Purifies Large Volumes of Water
Most water filters simply trap living bacteria as it passes through a series of tiny pores, a method that is effective but prone to a variety of problems. For one, they are painfully slow, and in disaster situations that can lead to critical shortages as thirsty populations wait for the water to trickle through.
Further, the water must be driven through the filters with pumps, which themselves require a decent amount of electricity – a resource that can be in short supply in remote regions or at disaster sites. Such filters are also susceptible to biofouling, in which trapped bacteria form a film that clogs the pores of the filter.
The Stanford team’s filter circumvents most of these problems by simply letting the bacteria pass freely through, zapping them with fatal doses of voltage as they go. By dipping plain cotton cloth procured at Wal-Mart into a solution of carbon nanotubes and silver nanowires, the team created a filter that can kill 98 percent of Escherichia coli bacteria in water with a mere 20 volts of electricity, less than is required to operate the pumps on conventional filters.
Addressing the problems with conventional filters noted above, the team knew that carbon nanotubes are efficient conductors of electricity and that silver has bacteria-killing chemical properties. So they went about figuring out how to get all these ingredients into a single, inexpensive filter (the amount of silver used is so small that it’s negligible). The cotton simply serves as an inexpensive platform on which to lay their nanotube/nanowire structure.
Plugged into a couple of 12-volt batteries or a hand cranked generator, the filter can run until the energy runs out, its larger pores letting vast volumes of water pass quickly, and cleanly, through. No pump is needed because the pores are large enough that gravity does the trick.
The next step is trying the filter on various other bacteria to see how universal the silver-carbon combo really is. One filter can kill 98 percent of the Escherichia coli in water, but a compound filter with layers of different materials might be able to push that number even closer to 100 percent for a variety of bacteria known to cause water-borne illnesses.
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California’s First Full-Scale Desalination Plant Lets Residents Drink the Pacific Ocean
The plant could produce more than 98 million gallons of drinking water per year
The brackish water treatment plant is expected to provide up to 98 million gallons (370 million liters) of drinking water per year, and cut down on that amount of water drawn from the Carmel River and Seaside Aquifer reservoirs.
Desalination works in this case by forcing seawater through a semipermeable membrane to separate out the salt. The $11.9 million plant operated on a test basis for more than a year, but only recently received permission from the California Department of Public Health to connect directly to the water grid serving the Monterey Peninsula.
Sand City has the good fortune to sit near a brackish coastal area where water is less salty than typical seawater -- and that means less energy and costs to desalinate. The city plant also uses reverse osmosis as its method of choice, rather than more expensive distillation which involves evaporating the water to separate it out from the salt.
The plant takes two additional steps to reduce its impact on marine life and to boost energy efficiency. First, it adds a special solution to the leftover salty brine that matches the salinity of Monterey Bay. And second, it uses special rotors to recover 98 percent of energy from the flow of salty concentrate, and puts that energy toward pumping seawater through the reverse osmosis membrane.
Desalination has become more and more attractive as a thirsty world looks for new freshwater sources. There's even a designed by MIT researchers that could provide drinking water for remote villages in the wake of disasters.
IBM researchers and scientists at Saudi Arabia's national research organization have also been working on water filtering technology that could create a breakthrough in solar-powered seawater desalination. Considering that an estimated 1.2 billion people still lack access to safe drinking water, we'll take what we can get.
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