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Title: Modeling nitrate removal in a denitrification bed

item GHANE, EHSAN - The Ohio State University
item Fausey, Norman
item BROWN, LARRY - The Ohio State University

Submitted to: Water Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2014
Publication Date: 1/31/2015
Publication URL:
Citation: Ghane, E., Fausey, N.R., Brown, L.C. 2015. Modeling nitrate removal in a denitrification bed. Water Research. 71:294-305.

Interpretive Summary: Nitrogen is an essential nutrient for agricultural crops. Farmers apply nitrogen fertilizer to assure an adequate source for crop needs. Some applied nitrogen is transported by runoff and drainage water to streams where it can cause harmful effects. A new practice to remove nitrogen from water before it reaches a stream is called a denitrification bed, also known as a woodchip bioreactor. This manuscript describes the development and testing of a model that can be used to design efficient, low cost woodchip bioreactors. This model will be useful to contractors, technical assistance agencies, and non governmental organizations.

Technical Abstract: Denitrification beds are being promoted to reduce nitrate concentrations in agricultural drainage water to alleviate the adverse environmental effects associated with nitrate pollution in surface water. In this system, water flows through a trench filled with a carbon media where nitrate is transformed into a harmless nitrogen gas under anaerobic conditions. The objective of this study was to evaluate and model a denitrification bed treating drainage water. Evaluations showed very low greenhouse gas surface emission from the denitrification bed. Field experiments indicated that nitrate removal rate was best described by Michaelis-Menten kinetics with the constant (K_M) of 7.2 mg N L-1. A temperature coefficient of 1.118 was calculated which accounts for the effect of initial nitrate concentration on nitrate removal rate. A novel deterministic model of a denitrification bed was developed based on Forchheimer’s equation and nitrate removal kinetics. The model evaluation statistics indicated good agreement of the predicted and measured bed outflow nitrate concentrations (R2=0.87) under natural tile flow conditions. In conclusion, this model can be used to design efficient nitrate removal denitrification beds which in turn will lead to enhanced drainage water quality.