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ARS Home » Northeast Area » University Park, Pennsylvania » Pasture Systems & Watershed Management Research » Research » Publications at this Location » Publication #331775
Title: Enhanced denitrification bioreactors hold promise for Mid-Atlantic ditch drainage

Author
item CHRISTIANSON, LAURA - University Of Illinois
item COLLICK, AMY - University Of Maryland Eastern Shore (UMES)
item Bryant, Ray
item ALLEN, ARTHUR - University Of Maryland Eastern Shore (UMES)
item BOCK, EMILY - Virginia Tech
item Kleinman, Peter
item MAY, ERIC - University Of Maryland Eastern Shore (UMES)
item EASTON, ZACHARY - University Of Maryland Eastern Shore (UMES)

Submitted to: Journal of Soil and Water Conservation Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/13/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: This work evaluated the practical design and installation concerns, edge-of-field monitoring challenges, and early nitrate removal performance of three categories of denitrifying bioreactors in the Mid-Atlantic. A tile drainage bioreactor, a novel in-ditch bioreactor, and two sawdust-amended denitrification groundwater walls were constructed between fall 2014 and winter 2015 in Virginia and Maryland. The sawdust walls were the easiest of the three types of bioreactor to install, whereas the in-ditch bioreactor was more intensive to design and install due to its novelty. All three categories of bioreactor exhibited nitrate removal, which showed promise for denitrifying bioreactor applications in this region. Lower than expected nitrate removal by the tile bioreactor was likely due to a combination of site/design constraints, potential internal short-circuiting, and water chemistry. The in-ditch bioreactor averaged 65% nitrate concentration reduction, but flow monitoring will be a critical part of future assessment of this proof-of-concept design. Observed sedimentation of the in-ditch bioreactor is expected to be one of the biggest practical challenges for in-ditch denitrification practices. The N removal rates for the two sawdust walls were consistent with past literature. Obtaining a robust water balance by monitoring inflow, outflow, and by-pass flow for these types of practices is critical for future assessment of their overall contribution to N load reduction and water quality improvement in the Mid-Atlantic.

Technical Abstract: There is strong interest in adapting treatment technologies such as wood-based denitrifying bioreactors to mid-Atlantic drainage systems to help address Chesapeake Bay water quality goals. This work evaluated the practical design and installation concerns, edge-of-field monitoring challenges, and early nitrate removal performance of three categories of denitrifying bioreactors in the Mid-Atlantic. A tile drainage bioreactor, a novel in-ditch bioreactor, and two sawdust-amended denitrification groundwater walls were constructed between fall 2014 and winter 2015 in Virginia and Maryland. The sawdust walls were the easiest of the three types of bioreactor to install, whereas the in-ditch bioreactor was more intensive to design and install due to its novelty. Challenges were encountered when siting the tile bioreactor (space limitations) and in-ditch bioreactor (wetland determination, additional permitting will be required if operating in a “waters of the United States”). Nevertheless, all three categories of bioreactor exhibited nitrate removal during these short monitoring periods, which showed promise for denitrifying bioreactor applications in this region. Lower than expected nitrate removal by the tile bioreactor was likely due to a combination of site/design constraints, potential internal short-circuiting, and water chemistry (5.0% annual N load reduction; 0.49 g NO3-N removed m-3 d-1, 0.00003 lb N ft-3 d-1). The in-ditch bioreactor averaged 65% nitrate concentration reduction, but flow monitoring will be a critical part of future assessment of this proof-of-concept design. Observed accumulation of sediment on the surface of the in-ditch bioreactor indicates that reduced infiltration due to sedimentation may be one of the biggest practical challenges for in-ditch denitrification practices. The N removal rates for the two sawdust walls centered around 0.90 and 0.30 g NO3-N removed m-3 d-1 (0.00006 and 0.00002 lb N ft-3 d-1) assuming a wide range of groundwater flow velocities), consistent with past literature. Obtaining a robust water balance by monitoring inflow, outflow, and by-pass flow for these types of practices is critical for future assessment of their overall contribution to N load reduction and water quality improvement in the Mid-Atlantic.