Woodchip Properties after Four Years in a Denitrification Bed.

Current agricultural production management practices rely on extensive use of nitrogen fertilizers. Nitrogen present in the soil are transported along with drainage water into surface water bodies creating surface water quality issues. Denitrification beds (or woodchip bioreactors) are large trenches filled with woodchips that reduce the transport of nitrate load in drainage water through a microbial transformation to nitrogen gas. Woodchip physical (i.e., permeability) and chemical (carbon to nitrogen ratio) properties are an important component to the success of denitrification beds. However, woodchip hydraulic property values determined under laboratory conditions are still scarce. Thus, there is a need to determine woodchip permeability values to provide input for denitrification bed modeling and design tools. The objective of this research was to evaluate four year old woodchip physical and chemical properties. Woodchips excavated from a four year old denitrification bed in Willmar, Minnesota were evaluated for hydraulic conductivity and particle size distribution. Preliminary results showed that water flow through four year old woodchips is non-Darcian, and is described by Forchheimer’s law. Carbon to Nitrogen (C/N) ratio showed that decomposition was significantly greater in the inlet of the bed. The applied significance of this research is that it will help enhance surface water quality.