PALO ALTO, Calif. -- By imitating and enhancing the natural cleansing functions performed by wetland ecosystems, constructed wetland treatment systems can successfully treat a variety of wastewaters. In an award-winning project designed, built, and co-funded by the Electric Power Research Institute (EPRI) and Allegheny Power, a constructed wetland is providing cost-effective treatment of a metal-bearing leachate from a closed ash management facility near Springfield, Pennsylvania.
"In constructed wetlands, the physical, chemical, and biological cleansing processes intrinsic to natural wetland ecosystems occur in a highly engineered environment," says John Godrich-Mahoney, manager for water quality R&D in EPRI's Environment Program. "By controlling, amplifying, and accelerating these processes, we can develop passive, low-cost systems optimized for the removal of specific chemicals of interest such as trace metals."
The Springdale wetland was installed in fall 1995. It includes an equalization basin and eight treatment cells that were selected, sequenced, and sized based on leachate characteristics. Since being brought on line, the system has removed an average of 97 percent of total iron and 98 percent of dissolved iron, bringing the discharge well under the National Pollutant Discharge Elimination System (NPDES) permit limit for this constituent. In addition, removal efficiencies average 89 percent for manganese and 79 percent for aluminum. Significant fractions of the trace elements arsenic, beryllium, molybdenum, nickel, and zinc are also being extracted.
"Our constructed wetland not only achieves NPDES compliance, but is also more cost-effective than conventional chemical systems," says Richard Herd, strategic environmental management advisor at Allegheny Power. "We estimate that the technology will save more than $2.6 million in operating and maintenance costs over the next 50 years."
In recognition of the Springdale system's outstanding design and performance, Allegheny Power recently received the 1997 Governor's Award for Environmental Excellence from the Pennsylvania Department of Environmental Protection. The company was also granted a 1996 Industrial Excellence Award from the Pennsylvania Water Environment Association for the most promising and cost-effective new wastewater treatment system in Pennsylvania.
EPRI is directing a comprehensive program to develop constructed wetland design and engineering guidelines for metal-bearing utility waste streams. The program includes demonstration projects, such as the Springdale installation, to broaden the power industry's experience base; field and laboratory research to increase mechanistic understanding of treatment processes; and experimental work to accelerate or otherwise enhance removal of individual chemicals.
Says Goodrich-Mahoney, "EPRI's program is introducing new dimensions to constructed-wetlands technology. Efforts to optimize these processes are on the leading edge of microbiology, plant physiology, genetic engineering, and other disciplines."
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