Faculty - Research - Constructed Wetlands Treat Barn
RunoffFor two years, Meghan Oldfield was literally
knee-deep in her research at a Dover-Foxcroft area dairy farm. As
a masters degree student in the UMaine Department of Civil and
Environmental Engineering, she donned rubber waders every week and
carried sample bottles, a testing meter and a note pad through the
brown soup she euphemistically called dairy barn wastewater.
Above the manure settling basin, the cattails and the lagoons
where Oldfield worked, a metal-roofed barn sprawls across the top
of the hill. Inside are about three hundred dairy cows, and at the
bottom of the hill runs the Piscataquis River. Wastewater flowing
out of the barn must be treated before it enters the river, and
the problem is finding a treatment method Maine dairy farmers can
afford.
The project determined how a constructed wetland could be used
to help treat the wastewater. It was a collaboration between
former department chair Chet Rock (who is now Associate Dean for
the UMaine College of Engineering), engineering students, farm
owner Richard Varnum and the federal government. The project was
designed and built by Rock, Rob Kostinec (a former graduate
student), Oldfield, undergraduate students and Varnum. Financial
support was provided by the U.S. Geological Survey through the
UMaine Water Research Institute.
"The goal was to remove as much of the manure and nutrients as
possible," says Oldfield. "The river is the bottom line. This
system is beneficial to the farmer due to its low maintenance
requirements and low cost."
Varnum's cows are milked three times a day, and the barn serves
as a watershed of sorts. On one side, milk flows into the farm's
storage tanks and eventually into Maine's $98 million-a-year dairy
industry. On the other side, wastewater carries a heavy load of
manure, bacteria and nutrients toward the river. If the river
carries such wastes, potential recreational activities are lost
and the river's ecological community changes. Around the country,
farmers and government agencies spend millions of dollars to
address such problems.
Constructed wetlands are a hot topic in environmental
engineering, but Maine's cold climate limits their application
here. They are used extensively in southern climates to meet high
standards of wastewater treatment.
In 1994, using his own equipment, Varnum dug a swimming pool
sized area below the barn for the settling basin and cattails. The
area was divided into four sections by wooden boards which are
notched to allow water to flow from one section to another. A
large diameter plastic pipe carries wastewater from the barn to
the first section.
In 1995, a second series of pools was dug. The wastewater was
evenly divided between the cattails and the new pools which, in
engineering language, are called lagoons. The lagoons hold water
and aerobic bacteria, but no large plants. The bacteria use oxygen
to decompose the waste.
Oldfield's work focused on evaluating the performance of the
lagoons and the cattails. In each area, the water is held long
enough for chemical and biological processes to take place before
it was allowed to seep into the river.
"The wastewater was really strong," Oldfield says. "The cattail
ponds were originally designed to treat all the waste, but they
were removing only about 40% of the contaminants. That wasn't
sufficient. We decided to build the lagoons, partly to take some
of the load off the cattails."
Oldfield's monitoring program showed that both systems together
initially removed about 80% of the contaminants. But, over the
long run, they were found only to remove about half of the solids
and organics in the wastewater. One major problem was their
performance during the winter. The lagoons continue to work during
the cold months, but the removal decreases as the biological
processes get slower.
"This technology involves engineering, chemistry and biology,"
Oldfield adds. "A successful system has to have all three."
Oldfield's thesis, entitled "Constructed Wetland and Aerobic
Lagoon Use in the Treatment of Dairy Milkhouse Wastewater in
Maine" was published in 1996. Its final recommendations suggested
that constructed wetlands and aerobic lagoons cannot adequately
treat milkhouse wastewater, due to the high amount of organic
material it contains. However, with design alterations, a similar
system could work. One alternative is the use of anaerobic
(bacteria that do not require oxygen) lagoons followed by
facultative ponds and wetland cells for final treatment. It was
also recommended that farmers find ways to decrease the amount and
strength of wastewater to be sent to treatment.
Oldfield came to UMaine after graduating from
Michigan Technological University in Houghton, Michigan.
"Before coming here, I talked with a lot of people, and they were
very friendly and encouraging," she says. "I've found the
department a great place to work." She earned her master's degree
in December of 1996 and is now employed as an environmental
engineer in Michigan.
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