United States
Environmental Protection
Agency
EPA/540/F-92/001
February 1992
&EPA
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
Emerging Technology Bulletin
Constructed Wetlands Treatment for
Toxic Metal Contaminated Waters
Colorado School of Mines
Technology Description: The constructed wetlands-based
treatment technology uses natural geochemical and biological
processes inherent in a man-made wetland ecosystem (see Fig-
ure 1) to accumulate and remove metals from influent waters.
The treatment system incorporates principal ecosystem compo-
nents found in wetlands, including organic soils, microbial fauna,
algae, and vascular plants.
Influent waters, which contain high metal concentrations and
have a low pH, flow through the aerobic and anaerobic zones of
the wetland ecosystem. Metals are removed by filtration, ion
exchange, adsorption, absorption, and precipitation through geo-
chemical and microbial oxidation and reduction. In filtration,
metal flocculates and metals that are adsorbed onto fine sedi-
ment particles settle in quiescent ponds or are filtered out as the
water percolates through the soil or the plant canopy. Ion
exchange occurs as metals in the water come into contact with
humic or other organic substances in the soil medium. Oxidation
and reduction reactions that occur in the aerobic and anaerobic
zones, respectively, play a major role
hydroxides and sulfides.
in removing metals as
Waste) Applicability: The wetlands-based treatment process
is suitable for acid mine drainage from metal or coal mining
activities and other leachates or wastewater that are mildly acidic
or mildly alkaline and contain toxic metals. Wetlands treatment
has been applied with some success to wastewater in the east-
ern regions of the United States. The process may have to be
adjusted to account for differences in geology.
Test Results: The final year of funding for the project under
the Emerging Technology Program was completed in 1991. The
funding was used to build, operate, monitor, and assess the
effectiveness of a constructed wetlands in treating a portion of
the discharge of acid mine drainage from the Big Five Tunnel
near Idaho Springs, Colorado. Results of the study have shown
that by optimizing design parameters, removal efficiency of heavy
Dam
Anaerobic Zone
Aerobic Zone
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Figure 1. Typical Wetland Ecosystem.
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mttals from the discharge can approach the removal efficiency of
chemical precipitation treatment plants. An example of the opti-
mum results from the 3 years of operation are as follows:
pH was raised from 2.9 to 6.5.
Dissolved aluminum, cadmium, chromium, copper, and
zinc concentrations were reduced by 98 percent or more.
Iron was reduced by 84 percent.
Lead was reduced by 94 percent.
Nickel was reduced by 84 percent or more.
Manganese removal was relatively low with reduction
between 9 and 44 percent.
• Bbtoxtclty to fathead minnows and Ceriodaphnia was
reduced by factors of 4 to 20.
On® of the final goals of this project will be the development of a
manual that discusses design and operating criteria for construc-
tion of a full-scale wetland for treating acid mine discharges. This
manual will be available in the Spring of 1992.
In 1990, the pilot-scale constructed wetlands system, .won a
"National Honor Award" In the Engineering Excellence Awards
competition of the American Consulting Engineers Council.
As m result of the success of this technology in the SITE Emerg-
ing Technology Program, it has been selected in the Records of
Decision (RODs) for both the Clear Creek Site in Colorado and
the Buckeye Landfill Site in Eastern Ohio. The full-scale 'con-
structed wetlands employed to remediate the discharge of the
Burleigh Tunnel near Silver Plume on the Clear Creek/Central
Cfty Site will be evaluated as a SITE Demonstration Project
under Cooperative Agreement with the state of Colorado.
For Further Information:
EPA Project Manager:
Edward Bates
U.S.JEPA Risk Reduction Engineering Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
(513) 569-7774 (FTS: 684-7774)
Technology Developer Contact:
Dr. Thomas Wilderman
"Colorado ^School of Mines
Golden, CO 80401
303-273-3642
United States
Environmental Protection
Agency
Center for Environmental
Research Information
Cincinnati, OH 45268
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EPA/540/F-92/001
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