| "It can be a multimillion dollar mistake if you build the wrong type." | |
| Ray Church, New Hanover County Department of Environmental Management |
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Garbage in a landfill can produce polluted discharge even 30 years after it's been buried, and traditional methods for cleaning the waste can be costly and unattractive. A 6-year-old pilot program in New Hanover County, North Carolina, is showing that using man-made wetlands can be an economic and environmentally friendly way to cleanse this wastewater.
"Constructed wetlands treatment systems offer many advantages over conventional treatment. They are aesthetically pleasing, more economical, provide wildlife habitat, offer opportunities for environmental education and research, and fit into our landfill's post-closure plan" of becoming a county park, says Samuel P. Hawes IV, an environmental technician with the New Hanover County Department of Environmental Management.
"Our goal is to eliminate discharge totally," says Ray Church, the department's director. "We're hoping that other communities will realize that what we're doing here is something that could benefit them as well."
In 1995, the department began a pilot study to determine the feasibility of using constructed wetlands to treat landfill-generated wastewater, commonly called leachate. Study findings determined this method was effective and could be an alternative to more traditional methods of treating leachate prior to discharge.
The Pollution Problem
Leachate forms in landfills when water from rain, sleet, or snow soaks through and becomes polluted after coming into contact with the decaying waste. All landfills generate leachate, even those that are closed and abandoned. The challenge facing landfill operators is to develop viable systems for treating leachate for at least 30 years following final closure of a landfill.
In 1981, New Hanover became the first county in the state to build a lined landfill to prevent pollutants from leaching into surface and ground waters. Drainpipes collect the leachate, which is processed in a small conventional treatment plant where microorganisms remove pollutants such as metals, ammonia, phosphorus, suspended solids, and oxygen-demanding waste. The treated waste is then discharged into the Northeast Cape Fear River, a major tributary of the Cape Fear.
"Over the years," Hawes says, "we have learned how to best handle this treatment system to maintain the highest quality treated leachate being discharged." He notes, however, that particularly during extremely cold weather, the treatment system can break down, resulting in leachate with high levels of ammonia nitrogen.
"We began experiencing difficulties" in meeting new water quality permit limits required by the North Carolina Division of Water Quality, explains Church. "Being biologists, we wanted to try to let nature do its thing." Using constructed wetlands for leachate treatment seemed like a possible alternative.
Working with Wetlands
The wetland discussion in the department centered on which type of wetlands to use: a surface flow wetlands where you see the water above the ground, or subsurface wetlands where the water moves unseen through the soil. "It can be a multimillion dollar mistake if you build the wrong type," Church notes.
Instead of choosing, Church says, the county was awarded a Coastal Area Management Act (CAMA) grant from the North Carolina Division of Coastal Management to build five wetland plots to test their ability to treat leachate, and to develop an environmental education program for elementary and middle school students to go along with it. The pilot system was researched by North Carolina State University for two years with funding from the Water Environment Research Foundation. Students from the University of North Carolina at Wilmington also were involved through internships and research programs.
Researching the Results
"The findings proved that our landfill leachate could be treated by constructed wetlands," Hawes says. For all parameters tested, the wetlands did as good a job as the treatment plant. But again, ammonia nitrogen posed a problem during cold weather.
"Ammonia nitrogen in our untreated leachate is quite high," Hawes explains. In the summer, nitrogen treatments can reach 90 to 95 percent effectiveness versus 25 to 30 percent in winter. Although nitrogen levels are too high in winter to discharge to the river, they are low enough to be irrigated onto closed landfill space. "If we irrigate on enough closed landfill space we can eliminate our discharge," he says.
"The final solution is that we don't discharge," Church notes. "We use the treated leachate back on the landfill [wetlands], and the nitrogen becomes a source of fertilizer for the plants."
Based on the research findings, the department was awarded a $785,000 grant from the North Carolina Clean Water Management Trust Fund to construct and operate a large wetland system to treat the landfill's 65,000 gallons of leachate a day. The system has been designed and is currently undergoing permit review by the state. This system will be the first of its kind in North Carolina.
Ed Beck, environmental engineer for the North Carolina Division of Water Quality, says his permitting agency is "cautious," but "open."
"I'm optimistic about constructed wetlands, and I would encourage regulators to be open to their possibility, but to review applications cautiously and to get as much information about the system in general that they can, in addition to the information presented in the application," Beck says.
Project Recognition
While it may be some time before the expanded plan is complete, New Hanover County's pilot project is garnering attention from other communities. In 2000, it was selected winner of a North Carolina Association of County Commissioners "Outstanding County Program" award, and Church notes that requests for information on the project have come from as far away as India and Thailand.
"From this day forward, wetlands treatment will be a part of our landfill," Hawes says. "I would recommend the technology to anyone that operates a treatment system of any kind in a temperate, mild climate. Wetlands work well on a wide range of contaminants. If coupled with spray irrigation, these systems can serve to reduce and/or eliminate discharges to surface waters. The only catch is, you need lots of land to irrigate on and to build a wetland system."
For more information on the New Hanover County constructed wetlands project, contact Ray Church at (910) 341-4340 or rchurch@co.newhanover.nc.us.
