New Colloidal Adsorbent Removes Natural Organic Matter From Water

Microbial degradation products and other forms of natural organic matter can make water look, smell and taste bad. Natural organic matter also can foul the membranes used in water treatment plants, significantly reducing their efficiency.

Now, a polymer-based colloidal adsorbent developed at the University of Illinois at Urbana-Champaign offers an environmentally friendly and cost-effective way of removing natural organic matter from municipal water supplies.

"Natural organic matter can react with chemical disinfectants such as chlorine to produce chloroform and other carcinogens in our drinking water," said Mark Clark, a professor of civil and environmental engineering at Illinois and a researcher at the Center of Advanced Materials for Purification of Water With Systems. "Ensuring a safe and clean water supply without forming dangerous byproducts is a major problem."

One solution, he said, is to remove more of the harmful bacteria by using advanced filtration processes that utilize synthetic membranes made from polymer. Less chlorine would then be needed, which would reduce the formation of potentially dangerous chlorinated compounds. The problematic membrane fouling from natural organic matter could be avoided by adding the new colloidal adsorbent.

Several years ago, Clark and Robert Riley, a polymer chemist with Separation Systems Technology in California, invented the technology for producing a colloidal adsorbent from polysulfone – the same organic polymer used for water purification membranes. A patent was issued late last year.

To create their cleaning colloids, Clark and his students inject a solution of polysulfone into water under controlled mixing conditions. The polysulfone precipitates into colloidal particles about 50-60 nanometers in diameter, which then aggregate into clusters about 12-20 microns in diameter.

The pore size of the clusters is perfect for trapping natural organic matter, Clark said. The very high surface area of the particles also creates a large adsorption capacity.

"The particles work better than activated carbon for collecting natural organic foulants … The colloids can be easily regenerated chemically, and they significantly reduce membrane fouling," Clark explained.

Not all natural organic matter fouls membranes, however. "A large percentage passes through the membrane with no problem," he said. "Only about 5 to 10 percent of the material actually causes a problem."

Now that the researchers have trapped the troublesome material in their adsorbent, they want to analyze it with advanced organic chemistry techniques. "We want to identify the material and characterize the nature of its interaction with the adsorbent," said Clark, who will discuss the colloidal adsorbent at the 228th American Chemical Society national meeting in Philadelphia. "Then we can look for ways to further improve both the adsorbent and the membrane."

The National Science Foundation and National Water Research Institute funded this work.

University of Illinois