Location: Soil and Water Management ResearchTitle: Nitrate removal and nitrous oxide production from upflow and downflow column woodchip bioreactors
|STROCK, JEFFERY - University Of Minnesota|
|MULLA, DAVID - University Of Minnesota|
|RANAIVOSON, ANDRY - University Of Minnesota|
|COULTER, JEFFERY - University Of Minnesota|
Submitted to: Agricultural and Environmental Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2020
Publication Date: 8/10/2020
Citation: Feyereisen, G.W., Spokas, K.A., Strock, J.S., Mulla, D.J., Ranaivoson, A.Z., Coulter, J.A. 2020. Nitrate removal and nitrous oxide production from upflow and downflow column woodchip bioreactors. Agricultural and Environmental Letters. 5(1). Article e20024. https://doi.org/10.1002/ael2.20024.
Interpretive Summary: Woodchip bioreactors are a conservation practice that removes nitrate-nitrogen (N) from agriculturally impacted water. Water typically flows horizontally through the woodchip beds. Changing the design to vertical flow, either upflow or downflow, could reduce short circuiting. This paper reports on a lab experiment wherein vertical upflow and downflow laboratory columns were compared for nitrate-N removal and production of the greenhouse gas nitrous oxide. The columns were operated for three days per week at 12-hour hydraulic residence time (HRT) and four days at 2-hour HRT with carbon added. There were no differences in nitrate-N removal or nitrous oxide production between the flow directions, although the downflow columns tended toward lower nitrous oxide production at 2 hours and exhibited less variability. When combining results, nitrous oxide production was unexpectedly lower at 2 hours with carbon than at 12 hours without carbon. The addition of carbon resulted in bioclogging of the downflow columns, a problem that needs to be overcome prior to moving this practice to field scale. Addition of carbon at the shorter HRT resulted in a 2.6-fold increase in nitrate-N removal rate. 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.
Technical Abstract: Woodchip bioreactors reduce off-field tile drainage nitrogen (N) losses from agricultural fields. Limited evaluation exists regarding the influence of flow direction through bioreactors. Changing flow direction could reduce short circuiting. This study evaluated the dependency of nitrate-nitrogen removal and dissolved nitrous oxide (dN2O) production rates on vertical flow direction in triplicate column bioreactors at 12-h and 2-h (with carbon dosing) hydraulic residence times. Results presented demonstrate that there was no significant difference in overall nitrogen removal rates from these column bioreactors as a function of flow direction. There was the suggestion of lower N2O production in the downflow direction, although this was not statistically significant due to the high variability of the N2O production observed in the upflow direction. Carbon addition led to bioclogging of downflow columns, which needs to be addressed in the future.