Effectiveness of denitrifying bioreactors on water pollutant reduction from agricultural areas

Authors: CHRISTIANSON, LAURA - University Of Illinois; COOKE, RICHARD - University Of Illinois; HAY, CHRISTOPHER - Iowa Soybean Association; HELMERS, MATTHEW - Iowa State University; Feyereisen, Gary; RANAIVOSON, ANDRY - University Of Minnesota; MCMAINE, JOHN - South Dakota State University; MCDANIEL, RACHEL - National Oceanic & Atmospheric Administration (NOAA); ROSEN, TIMOTHY - Shorerivers; PLUER, WILLIAM - University Of Waterloo; SCHIPPER, LOUIS - University Of Waikato; DOUGHERTY, HANNAH - University Of Waikato; ROBINSON, RHIANNA - Department Of Agriculture And Fisheries; LAYDEN, IAN - Department Of Agriculture And Fisheries; IRVINE-BROWN, STUART - Department Of Agriculture And Fisheries; MANCA, FABIO - Queensland University Of Technology; DHAESE, KRIS - Pcfruit; NELISSEN, VICTORIA - Pcfruit; VON AHNEN, MATHIS - Technical University Of Denmark

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2020
Publication Date: 1/1/2021
Citation: Christianson, L.E., Cooke, R.A., Hay, C.H., Helmers, M.J., Feyereisen, G.W., Ranaivoson, A.Z., McMaine, J.T., McDaniel, R., Rosen, T.R., Pluer, W.T., Schipper, L.A., Dougherty, H., Robinson, R.J., Layden, I.A., Irvine-Brown, S.M., Manca, F., Dhaese, K., Nelissen, V., Von Ahnen, M. 2021. Effectiveness of denitrifying bioreactors on water pollutant reduction from agricultural areas. Transactions of the ASABE. 64(2):641-658. https://doi.org/10.13031/trans.14011.
DOI: https://doi.org/10.13031/trans.14011

Interpretive Summary: Denitrifying bioreactors are a conservation practice that removes nitrate-nitrogen (N) from water primarily by the process of microbial denitrification. This paper is a review of bioreactor nitrate-N removal performance in the U.S. (Midwest, East Coast), New Zealand, Australia, Belgium, and Denmark, includes some cost-of-removal information, and outlines some current research work. The studies primarily covered bed-style bioreactors in tile-drained agricultural settings, but included other configurations, i.e., ditches and denitrification walls, and other applications, i.e., aquacultural effluent. Studies generally showed that woodchip denitrifying bioreactors leach phosphorus, especially on start up. The median nitrate-N removal rate for 27 studies was 5.1 g N m-3 d -1 (0.0086 lb. N yd-3d-1). Reported cost of nitrate-N removal varied widely from $2.50 to approximately $20 kg N-1, ($1.13 to $9.07 lb. N-1), with a highest report of $48 kg N-1 ($22 lb. N-1). The paper includes recommendations for basic performance monitoring of bioreactors. The findings of this research are pertinent to researchers, practitioners, academics, and agency personnel with interest in using denitrifying bioreactors to remove nitrate-N from water and in monitoring their performance.

Technical Abstract: Denitrifying bioreactors enhance the natural process of denitrification in a practical way to clean nitrate-nitrogen (N) from a variety of N-laden water matrices. The design and construction of bioreactors for treatment of subsurface drainage in the United States is guided by the United States Department of Agriculture Natural Resources Conservation Service Conservation Practice Standard 605. This review consolidates the state of the science for denitrifying bioreactors across the globe with an emphasis on full-size bioreactor nitrate-N removal and cost effectiveness. The focus is on bed-style bioreactors (including in-ditch modifications), although there is mention of denitrifying walls which broaden the applicability of bioreactor technology in some areas. The practice standard does not apply to denitrifying walls. The description of full-size bioreactor nitrate-N removal performance is organized as a series of case studies across wide geographies and applications (U.S. Midwest and East Coast, New Zealand, Australia, Belgium, Denmark). Subsurface drainage denitrifying bioreactors have been assessed as removing between 20 to 40% of annual nitrate-N loss in the Midwest, and an evaluation across peer-reviewed literature published over the past three years showed bioreactors around the world have been generally consistent with that (N load reduction median: 46%; mean±st dev: 40±26%; n = 15). Reported N removal rates were on the order of 5.1 g N/m3-d (median; mean±st dev: 7.2±9.6 g N/m3-d; n = 27). Subsurface drainage bioreactor installation costs have ranged from less than $5,000 to $27,000 with estimated cost efficiencies ranging from less than $2.50/kg N-y to roughly $20/kg N-y (although they can be as high as $48/kg N-y). Bioreactors in high-solids applications (i.e., not subsurface drainage) provide effective solids removal, but there is little field-scale data on such applications. Denitrifying bioreactors treating subsurface drainage show a mix of phosphorus leaching and removal, although most generally experience leaching at bioreactor start-up. A suggested monitoring set-up is described primarily for the context of conservation practitioners and watershed groups for assessing annual nitrate-N load removal performance of subsurface drainage denitrifying bioreactors. Recommended minimum reporting measures for assessing and comparing annual N-removal performance include: bioreactor dimensions and installation date; fill media size, porosity, and type; nitrate-N concentrations and water temperatures; bioreactor flow treatment details; basic in-field cropping and drainage system characteristics; and N removal rate and efficiency.