Agricultural and Biosystems Engineering Publications

Campus Units

Agricultural and Biosystems Engineering, Civil, Construction and Environmental Engineering

Document Type

Article

Publication Version

Published Version

Publication Date

2020

Journal or Book Title

Transactions of the ASABE

Volume

63

Issue

2

First Page

407

Last Page

416

Research Focus Area(s)

Land and Water Resources Engineering

DOI

10.13031/trans.13709

Abstract

There is a lack of information on denitrifying bioreactors treating subsurface drainage water at the end of their initial design life due to the relative newness of the technology and the relatively long estimated life. A denitrifying bioreactor (15 m L x 7.6 m W x 1.1 m D) installed in August 2008 in Greene County, Iowa, was recharged with new woodchips in November 2017 (age 9.25 years), providing the opportunity to evaluate the properties of the wood media at the end of design life. The objective was to pair a battery of physical, chemical, and nitrate-N removal tests on the wood media harvested from the bioreactor with field observations to assess likely reasons why denitrifying bioreactors treating tile drainage may need to be recharged. The two types of wood media harvested from the bioreactor (termed woodchips and mixed shreds) had median particle sizes (D50) of 12.1 and 7.7 mm, respectively, and saturated hydraulic conductivities of 4.2 ±3.0 and 3.1 ±1.0 cm s-1 (mean ± standard deviation), which were within the range of reported values for woodchips, albeit at the low end. The wood media carbon content and quality had degraded (e.g., lignocellulose indices of 0.63 to 0.74, nearing the range of decomposition stabilization), although batch tests suggested the robustness of wood as a carbon source to support nitrate removal (e.g., 65% nitrate concentration reduction in drainage water). Woodchip degradation along with sedimentation from the drainage system likely reduced conductivities over time. Development of preferential flow paths through the bioreactor was indicated by low bioreactor outflow rates (i.e., reduced permeability) and reduced hydraulic efficiency based on conservative tracer testing. These changes in media properties and linked impacts resulted in the need to recharge this bioreactor after nine years.

Comments

This article is published as Feyereisen, Gary W., Christopher Hay, Ulrike W. Tschirner, Keegan Kult, Niranga M. Wickramarathne, Natasha Hoover, and Michelle L. Soupir. "Denitrifying Bioreactor Woodchip Recharge: Media Properties after Nine Years." Transactions of the ASABE 63, no. 2 (2020): 407-416. DOI: 10.13031/trans.13709.

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Rights

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.

Language

en

File Format

application/pdf

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