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https://nap.nationalacademies.org/catalog/27432/critical-issues-in-transportation-for-2024-and-beyond

Retrofitting the Rural Roadside Ditch Network to Treat Nitrogen from Agricultural Runoff Using Woodchip Bioreactors

Nitrogen movement across the landscape has been indicated as a key contributor to the growth of the hypoxic zone in marine estuaries and is a concern on the federal level for watersheds like the Chesapeake Bay. Rural roadside ditches play a very significant role in nitrogen movement because they efficiently transport agricultural runoff to streams and rivers. Multiple well-tested best management practices (BMPs) (e.g., bio swales, woodchip bioreactor basins) for reducing nutrients already exist, but these have been primarily tested and used in large agricultural ditches or in situations where there is a single point of discharge such as a tile drain. In many agricultural settings, the topography and farm sizes do not lend themselves to treatment of agricultural runoff in large on-field ditches or as point sources. To address these issues, this study evaluated the potential of installing scaled-down woodchip bioreactors into roadside ditches for filtering dissolved nitrogen from agricultural activities. Although many different iterations and permutations of the woodchip bioreactor technology exist, all rely on heterotrophic denitrification to convert nitrate to nitrogen gas. By supplying a carbon source in a bioreactor, the nitrogen is effectively removed from the hydrologic system. This technology has been in use for over two decades with a considerable amount of research having been done on the topic over the past 10 years. The rate of removal varies tremendously depending on the influent concentrations, the size of the reactor, the contributing area, the type of land serviced, and the carbon source used. Additionally, contact time with the bioreactor media is an important variable in removal efficiencies, especially at low dissolved oxygen levels. A review found that in agricultural applications, large subsurface bioreactors saw removal rates of between 12% and 76% of the total load. The National Resource Conservation Service (NRCS) in Iowa has even issued a Conservation Practice Standard for the design of denitrifying bioreactors. More recently, testing of woodchip bioreactors in roadside ditches by Rebecca Schneider (co-author) showed promise with a nitrogen removal efficiency of 40% during the growing season. This study located in Bradford County, Pennsylvania, was undertaken by Pennsylvania State University Center for Dirt and Gravel Road Studies (the Center) and Cornell University to further study the potential for utilizing the rural roadside ditch networks as the basis for a low-cost agricultural lands filtration system. This project set out to monitor the treatment effectiveness and efficiency for removal of dissolved nitrogen contaminants using existing road ditches retrofitted with woodchip bioreactor socks. This study seeks to evaluate the effectiveness of the in-ditch woodchip bioreactor to remove nitrogen from agricultural runoff, and determine temporal changes in effectiveness and the environmental conditions such as temperature and flows that influence it. The results will be used to determine the total nitrogen removed and cost per pound of nitrogen reduced through the use of in-ditch woodchip bioreactors to support improvement of conservation practice standards.

Language

  • English

Media Info

  • Media Type: Digital/other
  • Features: Figures; Photos; References; Tables;
  • Pagination: pp 320-324
  • Monograph Title: 12th International Conference on Low-Volume Roads
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 01732652
  • Record Type: Publication
  • Files: TRIS, TRB, ATRI
  • Created Date: Mar 3 2020 4:02PM