Over the last decade, local groups have been working to reduce nitrogen loading in estuaries by exploring innovative treatment solutions for polluted groundwater. This fall, University of Chicago student Jonathan Pekarek took a new approach to the issue, turning his attention towards Falmouth’s streams.
Working with mentor Kenneth H. Foreman at Marine Biological Laboratory, Mr. Pekarek investigated whether permeable reactive barriers—an emerging denitrification technology—could be used to successfully remove nitrogen from streams and rivers. The project produced promising results, which Mr. Pekarek presented to members of the Falmouth Water Quality Management Committee last Thursday, December 15.
“We’re looking at a $600 million problem here, and trying to find alternatives to that: this is one of the more far-out possibilities,” chairman Eric T. Turkington said to Mr. Pekarek. “Frankly, no one has been thinking about it except the Town of Falmouth, and you.”
Permeable reactive barriers (PRBs) use a carbon source, such as wood chips, to prompt chemical reactions that break up nitrates in water. The carbon barriers are installed underground and upstream of groundwater plumes as a screen for polluted water, treating the water before it ever reaches local estuaries.
The barrier systems have been implemented in Falmouth over the past few years to treat groundwater, but have not yet been explored as an option for cleaning up local streams and rivers.
Streams are a major facilitator of nitrogen pollution because their fast-moving waters easily transport groundwater runoff to local estuaries. The same characteristic that makes streams such effective transporters of nitrates also makes them seemingly poor candidates for treatment by PRBs, which depend on the slow movement of water through wood chips for the denitrification process.
However, Mr. Pekarek found that the carbon barriers could remove nitrogen from local streams, given the right conditions.
Mr. Pekarek engineered pump systems to run sample stream water through cylindrical barriers filled with kiln-dried lumber wood chips, measuring the in-going and out-going nitrogen levels. Using the results of his laboratory studies, Mr. Pekarek developed a model to estimate the effectiveness of PRB systems in rivers under different conditions.
According to his model, Mr. Pekarek said that the town would need to install a barrier two meters deep and 0.78 acres large in order to remove 20 percent of the nitrogen from the Coonamessett River. A barrier of that size, he said, would provide the needed space to keep river waters flowing through the treatment area for an optimal 20 hours.
Before PRBs could be implemented in streams on a municipal scale, Dr. Foreman said, “you need a series of intermediate-size projects. This little lab study is the first foray into that.”
Dr. Foreman said a next step would be to take begin conducting field experiments in local streams.
“I think we’re now poised to do that over the summer pretty successfully,” he said.