Membrane filters offer options for cleaner water
18 Jun 2002
University of Houston researchers are studying how membrane filters, such as those currently used in some home water purification systems, might someday be used on a large scale to remove contaminants and organic compounds that can affect the purity and colour of municipal water supplies.
Understanding how such filters interact with various contaminants, including bacteria and other organic materials will help engineers devise more efficient filters, said Shankar Chellam, assistant professor of civil and environmental engineering at the University of Houston.
'Ultimately, the cost of membrane technology will go down and make it more feasible to be used for large-scale implementation,' Chellam said.
Membranes are made out of various materials and come with different pore sizes, which determine the size of the contaminants that can be filtered out. The goal is to optimise the combination of membrane material and pore size to fit any situation.
'Once we understand the complexities of how these membranes interact with contaminants, we can determine the properties that are needed to build into a filter. Ultimately, we could tailor-make filters for any contaminant in any water source, whether it's surface water or ground water, for example,' Chellam said.
Chellam's research group is studying various types of novel filtration membranes that might be used to remove the smallest of contaminants dissolved in water.
'The discoloration of water is often caused by dissolved organic matter. When you add chlorine to water for disinfection, it also bleaches the colour out of the water. The problem is, when chlorine interacts with the colour-causing organic material, the reaction forms cancer-causing compounds,' Chellam explained. 'Further, a recent report also claims that these compounds can cause birth defects and miscarriages.'
The generally followed approach in US water treatment plants is to remove as much of the colour-causing organic material from the water first, then add chlorine. However, Chellam said, conventional plants might be able to remove only about 50 percent of these organic materials.
'We are studying nanofiltration membranes that can remove 90 percent or more of natural organic material. In home devices, such filters can be changed after a few months or years, but you cannot do that in a large-scale plant that filters millions of gallons per day. It would be too expensive.
'Our research aims to determine exactly what happens to this organic matter, how it clogs up the filter and what happens to it after filtration, for example, as well as methods to reduce the formation of carcinogenic compounds. The long-term goal is for engineers to use our research to design better large-scale filtration systems,' Chellam said.
Chellam and his students not only are examining ways to better purify existing water supplies, but also how to deal with dirtier or more contaminated supplies. One project is focusing on developing portable membrane systems for producing drinking water in Texas border areas.
'As you move away from using the more pristine water supplies, you need more advanced purification processes. In addition, even with existing water supplies, we are learning more and more about chemical and microbiological risks that may be present in the environment. Any way you look at it, you may be forced to invent better water purification methods,' Chellam said.
Chellam will present information about his research on membrane filters June 20 in New Orleans at the annual meeting of the American Waterworks Association, http://www.awwa.org/ace2002/.
