One biotechnology that can reduce nitrate concentration in subsurface drainage water is called a denitrification bed. Bromide tracer testing has been used to determine the hydraulic properties of these systems to be used in design and modeling, but efficacy of bromide tracers has not been investigated. One important hydraulic property of woodchip beds is its in-situ effective porosity. The objectives of this study were to (1) determine if bromide is a suitable tracer for evaluating the hydraulics of woodchip beds based on laboratory sorption experiments and field tracer testing, and (2) to determine the in-situ effective porosity of denitrification beds. To achieve this goal, we conducted bromide sorption experiments in the laboratory, and conducted bromide tracer testing in seven denitrification beds near Willmar, Minnesota, USA. We did not find sorption (neither adsorption nor absorption) of bromide to woodchips in our laboratory sorption experiments. In contrast, bromide tracer tests showed an average bromide recovery of 82%, revealing that bromide was retarded in the woodchip denitrification beds. To the best of our knowledge, our experiment is the first study to estimate the in-situ effective porosity (average of 0.61) of a typical field-scale denitrification bed using a tracer test. A more accurate estimate of the actual hydraulic retention time (HRT) can be obtained by using the in-situ effective porosity rather than total porosity. Our laboratory experiment did not show any sorption of bromide to woodchips, but in contrast and for unclear reasons, our field tracer testing showed bromide retardation.
|Original language||English (US)|
|Number of pages||9|
|Journal||Journal of Hydrology|
|State||Published - Jul 2019|
Bibliographical noteFunding Information:
Funding of this research was provided in part by Minnesota Discovery, Research and Innovation Economy, and Minnesota Department of Agriculture Clean Water Fund. The funding sources were not involved in the study design, collection, analysis, interpretation of data, and preparation of the manuscript. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.
© 2019 Elsevier B.V.
- Denitrifying bioreactor
- Effective porosity
- Hydraulic retention time
- Subsurface drainage
- Tile drainage
- Woodchip bioreactor