College of Engineering Unit:
The OSU dairy barn’s main purpose is to support research and teaching for the Animal and Rangeland Sciences Department at OSU. There are roughly 240 cows in the herd. It is important to note that a single cow produces approximately 65 pounds of manure daily, which is high in nitrogen. The ammonia in the manure is converted to nitrite and subsequently nitrate by denitrifying bacteria in the soil. Surface water runoff from agriculture is a serious cause of nonpoint source pollution in the United States and around the world. The runoff carries nitrates from the field into the stream where they can adversely affect biological communities and spur algal growth, which can lead to harmful algal blooms and deplete oxygen in the water causing hypoxia, also known as “dead zones''.
The initial proposition was to convert an existing drainage ditch into a woodchip bioreactor that would decrease the runoff nitrate concentration to less than 10 mg/L. There is already a successful woodchip bioreactor on another part of the farm that reduces the nitrate concentration from a tile drainage system. What makes this situation unique is that the bioreactor’s water source is surface runoff and the ditch's proximity to Oak Creek.
To minimize the environmental impacts and cost and to ensure a sustainable design, we evaluated four alternative designs and used a decision matrix to select the best design. After determining the best approach, we decided to create a bioswale that diverted the runoff into a woodchip bioreactor. We constructed a scalable prototype of the bioreactors and conducted experiments to determine nitrate removal kinetics for different substrates. We built three bioreactors with just woodchips and three bioreactors with woodchips and biochar at a 9:1 ratio.