United States Department of Transportation
i
Removing Nitrate from Stormwater with Biochar Amendment to Roadway Soils
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2019-05-01
[PDF-1.16 MB]
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Edition:Final, 5/1/2017 – 5/31/2019
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Abstract:A combination of field and laboratory studies evaluated the impact of amending a wood-derived biochar to a roadway soil on stormwater runoff and water quality. At the field site, biochar amendment continued to demonstrate significant reductions in peak stormwater flow and cumulative runoff volume three years after construction. More limited water quality data indicate the biochar amendment reduced NO₃ and TN concentrations in subsurface water that percolates through biochar-amended soil. The primary benefit of biochar amendment on reducing stormwater pollutant loading, though, was the reduction in stormwater runoff volume. A companion column study was conducted using soil samples from the Delaware field site. A series of artificial storm events demonstrated that biochar positively affected volumetric moisture content, water infiltration, and total phosphorus reduction. However, both treatments leached total nitrogen and nitrate, with the biochar-amended columns leaching more than the native roadway soils. A separate column study incorporated biochar at the same application rate as the field site into four other field soils and also tested the application of compost to separate soil columns. This study also found improved hydrologic function from both amended soils, but in this case, both biochar- and compost-amended soils transported less nitrogen than native soils. Effluent from both unamended and biochar-amended soils showed substantial phosphorus and phosphate reduction, while reductions from compost-amended soils were lower. Differences between field and column data suggest that the mechanisms by which biochar affects nitrogen removal are complex and may be difficult to predict without a more fundamental understanding of biochar’s effect on microbial processes.
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