Smaller, Better, Faster Bioreactors: Do Baffles Improve Bioreactor Hydraulic Efficiency?.

Bioreactors for Illinois: Smaller, Better, Faster: evaluating bioreactor hydraulics with tracer tests Hannah Dougherty and Dr. Laura Christianson With the agricultural industry coming under fire for nutrient discharge into the world’s water supplies, there has been a call for more sustainable agricultural practices. This is an even larger issue in the Midwest, where many farms use extensive subsurface tile drainage systems to lower the water table to improve crop growth, increase traffic ability, and reduce risk. These tile drains allow nutrients, especially nitrogen, to mobilize directly into our waterways. Illinois, in particular, is one of the largest producers of nitrogen and phosphorus to the Mississippi River Basin, and has developed the Illinois Nutrient Loss Reduction Strategy as a guiding document to reduce overall nutrient loads from the state. Denitrifying bioreactors, which augment the naturally occurring denitrification process, are one of the recommended practices in the Illinois strategy. As bioreactors have been researched for a relatively short time, there is a need for more knowledge on design parameters. These ‘woodchip bioreactors’ need to be cost effective, practical, and compact, but efficient enough in nitrate loss reduction for landowners to use as an edge-of-field practice. This study used potassium bromide tracer tests to evaluate a new, potentially more compact bioreactor design that includes baffles. The bioreactor is 16.8 meters long, 10.7 meters wide and 0.91 meters deep in Pana, Illinois, USA. Installed in fall 2016 the nitrate removal has been evaluated across the entire system as well as from twelve monitoring wells placed throughout the bioreactor during installation. Tracer tests performed under several flow conditions allowed for the evaluation of its internal hydraulics. These results were then compared with published tracer test results from other more conventional bioreactors. Preliminary tracer testing and nitrate removal results will be presented.