United States Department of Transportation
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Simultaneous Removal of Nitrogen and Phosphorus from Stormwater by Zero-Valent Iron and Biochar in Bioretention Cells (Part 1)
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2016-06-03
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Alternative Title:Project Title: Simultaneous Removal of Nitrogen and Phosphorus from Stormwater by Zero-Valent Iron and Biochar in Bioretention Cells
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Edition:Final 1/1/15 - 11/30/16
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Abstract:Nutrients (N and P) in stormwater are a major cause of water quality impairments in the U.S. Current technologies such as bioretention cells to treat stormwater from roadways do not always remove nutrients sufficiently, and additional land may be needed to achieve the removal required by regulations. To improve performance of bioretention cells, we propose to use zero-valent iron (ZVI) and biochar in bioretention cells to remove nitrate (NO3 -) and phosphate (PO4 3-) from stormwater simultaneously. The primary goals of this project were to 1) understand how nitrate and phosphate are removed by biochar and ZVI, and 2) evaluate the performance of these media in a field-scale bioretention cell. This sub-report addresses the first goal and summarizes the laboratory work conducted at the University of Delaware. We conducted a series of batch experiments to study microbial nitrate degradation with biochar, and column experiments to assess the removal of phosphate by ZVI. Nitrate degradation was greatly enhanced in the presence of a wood biochar reduced either microbially (by the bacterium GS-15) or chemically (by dithionite). Electron balance calculations show this biochar possessed an electron storage capacity (ESC) of ca. 0.87 mmol/g that was available to microbes for nitrate reduction. Little phosphate removal from anoxic water was achieved by sand alone, whereas a removal of about 30% (8 or 16 ppm P) to nearly 100% (1.6 ppm P) was obtained when 5% ZVI (v/v) was added to sand columns. These results support the use of biochar and ZVI to improve bioretention cell performance with respect to nutrient removal, and justify additional studies to further develop this new stormwater treatment technology for large-scale deployment.
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