A new bioreactor system that serves up pollutants to "hungry" bacteria promises to clean up "unprecedented" levels of toxic organic chemicals classified as "priority pollutants" by the U.S. Environmental Protection Agency, according to Canadian researchers. The scientists envision its use in cleaning up contaminated sites and to get rid of old chemical supplies.
The development will be outlined in the Jan./Feb. print edition of the peer-reviewed journal Biotechnology Progress, published by the American Chemical Society (ACS), the world's largest scientific society. ACS Web publication of this paper was on Jan. 9.
The clean up takes place in two liquid phases. The first uses a solvent that the scientists say readily dissolves high concentrations of toxic chemicals such as benzene, toluene, and p-xylene (collectively referred to as BTX). These man-made chemicals are components of gasoline and also are used extensively in industrial processes. In the second phase, the BTX is fed to a Pseudomonas bacteria cultivated in water.
The pollutants are much more soluble in the solvent than in water, so a large amount of BTX can dissolve in the solvent phase of the two-phase bioreactor without leading to high concentrations in the water phase. This is beneficial because too much of the BTX can kill the bacteria. Since a strict equilibrium is maintained between the phases, BTX enters phase two only as fast as bacteria degrade what's already there. "The organisms themselves determine the rate at which the BTX gets fed to them," says the chemical engineer Andrew J. Daugulis, Ph.D., of Queen's University in Ontario. "They control the process. Therefore we have a very efficient and self-regulating means of destroying large quantities of (toxic chemicals)." The by-products are carbon dioxide and more bacteria.
To test their bioreactor, the researchers intentionally "spilled" BTX on soil. They say their solvent was able to recover more than 99% of the pollutants from the soil. When it was then put through the bioreactor, "the bacteria readily used up all of the BTX," according to Daugulis. "So we used the solvent again to recover another 'spill' and then sent it back to the bioreactor for BTX degradation. It worked as expected."
It is hoped that this reusable system might replace current clean-up procedures for some applications. Today's methods include spraying bacteria directly on contaminated sites, removing soil and washing it with large volumes of water, and incineration. All of these systems have major drawbacks. Because the new bioreactor is still in early laboratory testing stages, it is not yet clear what complications might occur during large-scale use.
The researchers think their system would be especially effective at getting rid of very high concentrations of toxic organic wastes like BTX, including stores of pure chemicals past their "use by" date. They say that, unlike conventional approaches, the higher the concentration of waste the better their bioreactor works.
A nonprofit organization with a membership of nearly 159,000 chemists and chemical engineers, the American Chemical Society publishes scientific journals and databases, convenes major research conferences, and provides educational, science policy and career programs in chemistry. Its main offices are in Washington, D.C., and Columbus, Ohio.
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