Denitrification bioreactors for nitrate removal in agricultural drainage have recently gained attention for their low cost and effectiveness. While research continues to investigate the optimal sizing of these systems, little work has been done on the optimal design geometry (Length to width ratio and cross sectional shape). To address this lack, pilot-scale (1/10th scale) work performed in Iowa during the summer of 2009 explored three shapes of potential bioreactor designs. The objective was to study the nitrate removal effectiveness of each design at various retention times. The pilot bioreactors had a standard volume (0.71 m3) and depth (0.61 m) and different dimensions of 0.76 m x 1.5 m (rectangle), 0.38 m x 3.0 m (channel), and 1.5 m x 1.2 m (trapezoidal). Steady state experiments consisted of the bioreactors being allowed to run at a given retention time for several days/weeks before being changed to a different retention time. A hydrograph flush experiment simulated a drainage hydrograph moving through the bioreactor over the course of a few days. Preliminary results indicated little significant difference between the designs though the channel design seems to provide the most consistent results between the two experiments. Further analysis of this data is expected to guide future full-scale denitrification bioreactor designs.