United States Department of Transportation
i
Wood Filters as an Innovative Treatment Method for Roadway Runoff Pollutants: Final Report
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2005-01-01
[PDF-618.16 KB]
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TRIS Online Accession Number:1002820
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OCLC Number:61112283
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Edition:Final report
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Abstract:A significant amount of contamination enters water bodies via stormwater runoff. To control this non-point source pollution problem, retention ponds are installed at many locations. In previous studies it has been shown that these ponds do not effectively remove dissolved constituents, such as heavy metals and PAHs. Results from previous laboratory tests suggest that wood fibers enhance the removal of dissolved contaminants from simulated runoff. Described in this report are the results of a pilot-scale wood filter test that was conducted at a retention pond in Providence, RI. One objective was to determine if wood fibers could effectively remove contaminants from the water under field conditions. A total of four filters were installed to determine sorption of nitrate, phosphate, copper, iron, zinc, and PAHs as a function of differences in wood mass, different residence times, and changes in temperature and pH. The wood filters effectively removed between 25% and 36% of the dissolved PAH contaminants. However, simple design changes promise to enhance the filter efficiency to about 50%. The heavier molecular weight PAH compounds, i.e. the PAHs with higher organic carbon partitioning coefficients (e.g. benzo(a)pyrene), sorbed more readily than the lighter molecular weight compounds. The PAH sorption effectiveness of aspen wood was not affected by temperature or pH; however, the greater the mass of wood, the greater the sorption and effectiveness. The wood fibers appeared to promote nitrification, increasing the nitrate levels in the water, especially in the winter. The filters were 24% effective in removing phosphate from the water, but the wood leached phosphate after installation for a few days. Both copper (29%) and iron (40%) were effectively removed, especially under slightly acidic conditions. Zinc results were inconclusive because of zinc leaching from the galvanized wire mesh used to contain the wood fibers. Intense precipitation caused the filter to be less effective, and even flushed PAHs off the filter. The laboratory tests demonstrated that Cedar wood is a very promising alternative to Aspen wood. Even after more than 50 days of continuous flushing with contaminated water, the PAH removal remained between 66% and 92%, depending on the compound studied.
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