Project Title

Removing Nitrate from Stormwater with Biochar Amendment to Roadway Soils

Collaborating Universities

University of Delaware
Newark, DE 19716

University of Virginia
351 McCormick Dr.
P.O. Box 400742
Charlottesville, VA 22904-4742

Principal Investigator(s)

Imhoff, Paul (UD)

Chiu, Pei (UD)

Culver, Teresa (UVA)

Total Project Costs


Start Date


Completion Date



Stormwater from roadways, wastewater facilities, and agricultural operations is a major contributor to deteriorating water quality in many watersheds in the U.S., particularly the Chesapeake Bay in the MidAtlantic region. Municipalities and state departments of transportation must find ways to control their discharge to comply with increasingly stringent regulations. Nutrients, such as nitrogen, are the leading cause of impaired water quality in the U.S. and worldwide. Current stormwater treatment technologies, such as bioretention ponds, do not always treat nutrients sufficiently and may require sizable real estate to achieve the necessary removal – unless new technologies are developed. Hence, there are strong environmental and economic incentives to develop new technologies that improve treatment, thus reducing the footprint to remove nutrients from stormwater. Such technologies would have significant financial and programmatic impact for state DOTs.

Research Goals and Objectives:  To address this challenge, with support from the Chesapeake Bay Stewardship Fund (CBSF) and the Delaware Department of Transportation, the University of Delaware (UD) constructed a field test site to evaluate biochar roadway soil amendment to reduce the volume of and nitrogen concentrations in stormwater runoff. By amending the top 30 cm of a 2-m wide side slope to a well-traveled state highway, the stormwater runoff volume was reduced by 67% on average over 36 storm events. In addition, nitrate concentrations, the most difficult to remove form of nitrogen, were reduced by approximately 50% in some of the limited storms sampled. These dramatic results suggest that biochar-amended roadway soils might allow DOTs to gain treatment credit with modest redesign of their currently owned highway greenways. However, the CBSF study will end in 2017 and insufficient data exist on the reduction in nitrate concentrations in stormwater runoff, since the focus of that study was stormwater hydraulics. Further, the quality of the stormwater infiltrating biochar-amended roadway soils was not determined in the CBSF study. Thus, it is unclear if reductions in nitrate concentrations in surface runoff also occur in infiltrating water, which is eventually discharged to nearby streams where it can affect regulated waters. Finally, while our laboratory studies have shown that biochar can act as an electron storage medium, providing electrons under anoxic conditions to enhance denitrification (Saquing et al., 2016), these experiments were conducted with a pure microbial strain. To convincingly demonstrate that biochar can promote nitrate reduction to innocuous nitrogen gas (N2) by common soil bacteria in the field, additional experiments are required.

The objectives of the proposed research are to (1) leverage the investment from the CBSF study ($643k) by simultaneously sampling stormwater that flows over and through biochar-amended soils at this field site to quantify biochar’s ability to reduce nitrate for both flow paths, (2) determine the necessary residence time for nitrate-laden stormwater in biochar-amended media for nitrate removal, and (3) confirm that biochar provides electrons to mixed bacterial cultures in soil to convert nitrate into innocuous nitrogen gas. Data from this study leverages a recent CBSF project and will provide a path forward for full-scale evaluation, design, and implementation of this novel and sustainable technology – biochar amendment of existing roadway soils.