Nitrate removal and N2O production from upflow and downflow column woodchip bioreactors

<p class="ParaText"><span>Woodchip denitrifying bioreactors (WDBR) reduce off-field tile drainage nitrogen (N) losses from agricultural fields.  Limited evaluation exists regarding the influence of flow direction through WDBRs.  <a name="_Hlk40339771">Changing flow direction could reduce short circuiting. </a> This study evaluated the dependency of nitrate-nitrogen removal and dissolved nitrous oxide (<i>d</i>N₂O) production rates on vertical flow direction in triplicate column bioreactors at 12-h (without carbon dosing) 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 nitrous oxide (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.  <a name="_Hlk43820284">Carbon addition led to bioclogging of downflow columns; future work needs to identify dosing rate, placement, and conditions that prevent biofilm formation.</a></span></p>