TimmyH
Simpler Cleaner Desalination
August 13th 2008 04:26
Access to clean drinking water is a daily challenge for more than a billion people. There are more than 7,000 desalination plants worldwide, with another proposed to Sydney by the NSW Government in Australia. More than 250 currently operate in the US.
Until now, the use of Chlorine in the system has been heavily criticised. But researchers in Texas and Virginia have engineered a chlorine tolerant membrane to filter salt. Researchers say that this could eliminate many of the energy expensive steps in the process and lead to a direct filtering process.
Most desalination plants currently use polyamide membranes. The problem with these is that they degrade quickly under continuous exposure to chlorine and chlorine is crucial to the process.
Ben Freeman, professor of chemical engineering a UT in Austin Texas says the new membrane could drastically improve the process by streamlining the number of steps. Freeman and James McGrath, of the Virginia Polytechnic Institute, engineered a water-filtering membrane that stands up to repeated exposures of chlorine.
The new membrane contains polysulfone which is highly resistant to chlorine. Up until recently, research has failed to overcome the thickness of membranes using this material because it does not easily let water pass through.
Freeman says that when researchers add such compounds after they synthesize the polymer, "eventually, you break the backbone of the polymer chain . . . to the point where it's not useful."
Instead, the team added two hydrophilic charged sulfonic acid groups and found that this produced a durable and reproducible polymer.
Salt permeability tests proved that the new polymer was effective for long periods of time. Freeman and McGrath found that the new membrane performed just as well as many commercial membranes in filtering out water with low to medium salt content. But for saltier samples comparable to seawater, the team's membrane was slightly less permeable.
"We have materials that are competitive today with existing nano filtration and some of the brackish water membranes," says Freeman. "We are now pushing the chemistry to get further into the seawater area, which is a significant market we'd like to access."
Chlorine sensitivity tests found that the membrane suffered little despite constant chlorine exposure for more than 35 hours. Normal membranes are usually eaten away by this time and lose the effectiveness.
Further testing will be conducted to improve the chlorine resistance in the coming months. The researchers are currently in talks with leading manufacturers of desalination membranes
"These membranes may represent a reasonable route to commercialization," says Freeman. "If we're successful, we'll have the possibility of basically making these membranes on the same equipment that people use today."
Eric Hoek, an assistant professor of civil and environmental engineering at the University of California, Los Angeles, says that the chlorine-tolerant membrane developed by Freeman's team may be a promising alternative to today's industrial counterparts.
"This work is among the most innovative and interesting research on membrane materials in the past decade," says Hoek. "While the chlorine tolerance exhibited by these membranes is impressive, the basic separation performance is not yet where it needs to be for these materials to be touted as immediate replacements of commercial seawater membrane technology."
Desalination Process
Until now, the use of Chlorine in the system has been heavily criticised. But researchers in Texas and Virginia have engineered a chlorine tolerant membrane to filter salt. Researchers say that this could eliminate many of the energy expensive steps in the process and lead to a direct filtering process.
Most desalination plants currently use polyamide membranes. The problem with these is that they degrade quickly under continuous exposure to chlorine and chlorine is crucial to the process.
Ben Freeman, professor of chemical engineering a UT in Austin Texas says the new membrane could drastically improve the process by streamlining the number of steps. Freeman and James McGrath, of the Virginia Polytechnic Institute, engineered a water-filtering membrane that stands up to repeated exposures of chlorine.
The new membrane contains polysulfone which is highly resistant to chlorine. Up until recently, research has failed to overcome the thickness of membranes using this material because it does not easily let water pass through.
Freeman says that when researchers add such compounds after they synthesize the polymer, "eventually, you break the backbone of the polymer chain . . . to the point where it's not useful."
Instead, the team added two hydrophilic charged sulfonic acid groups and found that this produced a durable and reproducible polymer.
Salt permeability tests proved that the new polymer was effective for long periods of time. Freeman and McGrath found that the new membrane performed just as well as many commercial membranes in filtering out water with low to medium salt content. But for saltier samples comparable to seawater, the team's membrane was slightly less permeable.
"We have materials that are competitive today with existing nano filtration and some of the brackish water membranes," says Freeman. "We are now pushing the chemistry to get further into the seawater area, which is a significant market we'd like to access."
Chlorine sensitivity tests found that the membrane suffered little despite constant chlorine exposure for more than 35 hours. Normal membranes are usually eaten away by this time and lose the effectiveness.
Further testing will be conducted to improve the chlorine resistance in the coming months. The researchers are currently in talks with leading manufacturers of desalination membranes
"These membranes may represent a reasonable route to commercialization," says Freeman. "If we're successful, we'll have the possibility of basically making these membranes on the same equipment that people use today."
Eric Hoek, an assistant professor of civil and environmental engineering at the University of California, Los Angeles, says that the chlorine-tolerant membrane developed by Freeman's team may be a promising alternative to today's industrial counterparts.
"This work is among the most innovative and interesting research on membrane materials in the past decade," says Hoek. "While the chlorine tolerance exhibited by these membranes is impressive, the basic separation performance is not yet where it needs to be for these materials to be touted as immediate replacements of commercial seawater membrane technology."
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