TECHNOLOGY UPDATE region in the soil influenced by plant roots. The project is funded in part by the Department of Defense Environmental Security Technology Certification Program. —KELLYN S. BETTS
BlOTECHNOLOGY Phytoremediation project taking up TCE Only one year after being planted, some cottonwood trees in a phytoremediation field demonstration appear to be taking up the trichloroethylene (TCE) contaminating the groundwater beneath them. The demonstration project became part of EPA's Superfund Innovative Technology Evaluation program this spring. The goal of the project at the Naval Air Station Joint Reserve Base Fort Worth (formerly Carswell Air Force Base) is to clean up TCE in a shallow, thin aerobic aquifer. Eastern cottonwoods were chosen because they are indigenous to the site; they are members of the same genus as poplar trees and grow at similarly rapid rates. As part of this project, saplings were planted in five-gallon buckets; and cuttings, called whips, were planted on a one-acre site. Using deep planting techniques such as augering, researchers want to determine whether the whips can absorb the TCE as readily as anchored trees. If so, significant cost savings may be realized. "There was TCE signature in the whip plantation where the groundwater was shallowest at the end of the first growing season," said project manager Greg Harvey, a certified industrial hygienist with the Aeronautical Systems Center's Acquisition Environmental Management Restoration Division. "We take this as presumptive evidence that some of the trees have intersected the capillary fringe at the site. The hope here isn't to clean up the entire site but merely to demonstrate take things at the toe of the plume and intercept them with purposefully planted trees " said Harvev "We're planting trees to intercept and reverse the flow gradient and dpfprmine if cottonwnnHs can m e tahnli*7P T P F a n d it's daii(yhtp»r m m
Biotrickling filter removes styrene
Glenn Rivers of the U.S. Geological Survey checks a monitoring well at a Fort Worth, Tex., phytoremediation field demonstration. (Couitesy Greg Harvey)
pounds under field conditions." Extensive monitoring of the site includes groundwater and vegetation chemistry samples, hourly depth-to-groundwater measurements, and plant enzyme determinations in plantations and nearby riparian trees. James Vose, a researcl ecologist from the U.S. Forest Service, called the transpiration data collected thus far "encouraging." "The bottom line is that those trees are transpiring a lot of water." When the evapotranspiration rate exceeds the rate of precipitation as it often does in central Texas the cottoriwood pl tints 3X6 forced to groundwater Furthermore that consumption can slow and change the flow of contaminated groundwater The scientists also expect the project to show that TCE will be cometabolized in the rhizosphere, the
0013-936X/97/0931-347A$14.00/0 © 1997 American Chemical Society
The first full-scale demonstration of a biotrickling filter for waste air treatment is being conducted in southern California. A prototype filtering system built by researchers at the University of California at Riverside (UC-Riverside) removes styrene from the waste airstream generated by Lasco Bathware, Anaheim, Calif. Biotrickling filters pass a stream of polluted air through a bed of inert packing material supporting a mixed culture of aerobic microorganisms known as a biofilm. Although essential mineral nutrients are provided through the aqueous scrubbing solution, the pollutants themselves are the bacteria's main food, which is used as a source of carbon and energy. The main byproducts of the ensuing biodegradation are carbon dioxide water and small amounts of biomass. Marc Deshusses, an assistant professor of chemical engineering at UC-Riverside, received a grant from the California Toxic Substances Research and Teaching Program to treat airstreams polluted with volatile organic compounds. Deshusses and Todd Webster, a postdoctorate, collaborated with Environmental BioSystems of Denver to construct a mobile reactor based on a design validated by three years of benchscale operation at the Swiss Federal Institute of Technology. Because of the large volume of waste generated by Lasco Bathware (each of its two stacks has an airflow of 50,000 m 3 /h), the prototype reactor is treating a side stream of contaminated air. The researchers have concentrated on maximizing the biotrickling reactor's elimination capacity. After operating the reactor for four months, Deshusses says it can remove 80% of the styrene entering
VOL. 31, NO. 8, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 3 4 7 A
