Denitrifying bioreactor surface subsidence varies with age and cover
Date
2024-11-22
Authors
Christianson, Laura E.
Christianson, Reid D.
Hay, Christopher H.
Seeman, Anthony
Díaz-García, Carolina
Feyereisen, Gary W.
Pease, Lindsay
Kjaersgaard, Jeppe
Major Professor
Advisor
Committee Member
Journal Title
Journal ISSN
Volume Title
Publisher
Elsevier B.V.
Abstract
Surface subsidence at denitrifying woodchip bioreactors treating subsurface drainage has been anecdotally noted but has not been consistently documented and is thus poorly understood. Subsidence is of concern due to safety and potential exacerbation of ponding within the bioreactor but could also indicate flow restrictions within the woodchip bed. This study used 3D light detection and ranging (LiDAR) surveying on handheld devices (iPhone 12 Pro, iPad Pro) to provide minimum estimates of surface subsidence at 17 full-size bioreactors across a range of ages (0.1 to 14 years). Bioreactors with woodchips extending to the surface subsided faster than bioreactors with soil covers with median subsidence rates over the entire surface of 7.3 and 1.0 cm/y, respectively. Maximum subsidence averaged 40 ± 14 cm across all sites and tended to occur near the inflow manifold where subsidence could disproportionately impact hydraulic performance. Although these findings are limited to the bioreactors in the present evaluation and other sites may show different trends, it may be that subsidence is not reducible to aerobicity alone. Subsidence is not necessarily, on its own, the best individual indicator of the end of design life. In practice, checking for a consistent reduction in the amount of outflow over time is the best way to assess the need for a bioreactor woodchip recharge. Nevertheless, in this study, subsidence at full-size bioreactors was successfully approximated using a hand-held LiDAR device, and use of this method at additional sites is suggested, especially following bioreactor construction.
Series Number
Journal Issue
Is Version Of
Versions
Series
Academic or Administrative Unit
Type
article
Comments
This article is published as Christianson, Laura E., Reid D. Christianson, Christopher H. Hay, Anthony Seeman, Carolina Díaz-García, Gary W. Feyereisen, Lindsay Pease, Jeppe Kjaersgaard, Matthew J. Helmers, and Michelle Soupir. "Denitrifying bioreactor surface subsidence varies with age and cover." Ecological Engineering 211 (2025): 107461.
doi: https://doi.org/10.1016/j.ecoleng.2024.107461.
Rights Statement
Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted.