Faculty Spotlight: Paul Imhoff, PhD, University of Delaware

Environmental Implications of Fluid Flow and Contaminants
on Roadway Soils and Waterways

Paul Imhoff, PhD

Earlier this year, MATS UTC announced eight collaborative research awards selected from 28 submissions, each a strong example of the consortium’s commitment to accelerating the adoption of sustainable transportation practices. Paul Imhoff, PhD, Professor in the College of Engineering at the University of Delaware (UDel), along with his colleagues, Pei Chiu, PhD at UDel, and Teresa Culver, PhD at the University of Virginia (UVA), received one of the awards to continue their work to improve stormwater treatment technologies.

Stormwater from roadways, other impervious surfaces in urban regions, and agricultural operations is a major contributor to deteriorating water quality in many watersheds such as the Chesapeake Bay. 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.

The team’s 2017 MATS UTC-funded project, “Removing Nitrate from Stormwater with Biochar Amendment to Roadway Soils, builds upon their earlier work using biochar, a ‘green charcoal’ produced from agricultural residues or renewable biomass such as wood chips, grass clippings or poultry waste, to remove or transform nitrate. Supported by the Chesapeake Bay Stewardship Fund (CBSF) and the Delaware Department of Transportation, this previous work found that amending the top 30 cm of a 2-m wide side slope to a well-traveled state highway with biochar resulted in a reduction of the stormwater runoff volume 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.

The team is now focused on using the same field site to simultaneously sample stormwater flowing over and through biochar-amended soils to quantify its ability to reduce nitrate concentrations in both flow paths. In addition, the researchers will determine the necessary residence time for nitrate-laden stormwater in biochar-amended media for nitrate removal, and confirm that biochar provides electrons to mixed bacterial cultures in soil to convert nitrate into innocuous nitrogen gas. Results are expected to provide a path forward for full-scale evaluation, design, and implementation of this novel and sustainable technology – biochar amendment of existing roadway soils.

Imhoff has spent much of his academic career contributing to our understanding of the transport of fluids and contaminants in multiphase systems, mass transfer processes in soil and groundwater and more recently green stormwater treatment. These interests have global implications. Currently working with the Gates Foundation, Imhoff is developing above-ground toilets for urban communities in India lacking sufficient resources and space to install septic systems. “We’re working with manmade membranes to leverage the flow and reaction of fluid around solid matter,” explained Imhoff. The study is still underway but Imhoff has high hopes for the humanitarian and environmental implications of the project on the welfare of these communities.

Additional research interests include addressing spills from fracking fluids that infiltrate surrounding soil, and developing methods to quantify and mitigate greenhouse gas emissions from landfills.

In addition to his research pursuits, Imhoff teaches courses in environmental engineering at UDel. Reflecting his commitment to sustainable landfilling and protection of our soil and water, his classes generally focus on recycling and solid waste management, groundwater flow and pollutant transport, and modeling environmental systems.

Near the start of his career, Imhoff received a National Science Foundation Faculty Early Career Development Award. He has since received a number of honors and awards, including the 2005 Distinguished Service Award from the Association of Environmental Engineering and Science Professors, the 2011 ASCE Outstanding Reviewer Award from the Journal of Environmental Engineering, and the 2016 Top Reviewer Award from Waste Management.

Imhoff received a BS from the University of Cincinnati, an MS from the University of Wisconsin at Madison, and his MA and PhD from Princeton University.

Imhoff may be contacted at imhoff@udel.edu.