Submitted to: Biosystems Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2009
Publication Date: 7/27/2009
Citation: Chun, J.A., Cooke, R.A., Eheart, J.W., Kang, M.S. 2009. Estimation of flow and transport parameters for woodchip based bioreactors: I. laboratory-scale bioreactor. Biosystems Engineering. 104:384-395. Interpretive Summary: Engineers have made various efforts to reduce the released nitrogen amount from agricultural fields including bioreactors, a system to stimulate biological processes. However, bioreactors have been designed and installed empirically, due to lack of flow and transport parameters. In this research, flow and transport parameters of the laboratory-scale bioreactor were estimated. These parameters can be used to improve the operation and the design of field-scale bioreactors. Farmers, Agricultural Engineers, and Agricultural extension specialists will benefit from this research.
Technical Abstract: In subsurface bioreactors used for tile drainage systems, carbon sources are used to facilitate denitrification. The objective of this study was to estimate hydraulic conductivity, effective porosity, dispersivity, and first-order decay coefficients for a laboratory-scale bioreactor with woodchips as the carbon source. The laboratory-scale bioreactor used in this study consisted of a polyvinyl chloride (PVC) pipe (0.254 m in diameter and 6.1 m in length) filled with woodchips, with a drainage control structure attached to each end. Creek water and deionized water with nitrate-N concentrations ranging from 8 to 33.7 mg/L was passed through the bioreactor at several flow rates. For the creek water runs, complete (100 %) nitrate-N reduction and approximately 10 to 40 % nitrate-N reduction were observed at high retention times and at low retention times, respectively. The model CXTFIT2 developed by Toride et al. (1999) was used to estimate hydrodynamic dispersion coefficients (dispersivity) and first-order decay coefficients. The dispersivity and the first-order decay coefficient of the bioreactor were determined to range from approximately 10 to 30 cm, and approximately 0 to 0.14 hr-1, respectively without any discernable temporal or spatial trend. From these laboratory-scale bioreactor studies, it is concluded that the assumptions of first-order decay and no sorption for nitrate-N transport are justified for each single run. Based on this conclusion, it may be inferred that microbial denitrification is the main process through which nitrate-N concentration is reduced in the laboratory-scale bioreactor. It is concluded that woodchip based bioreactors may contribute to significant nutrient reduction from artificially drained agricultural field by tile drain systems.