Nitrous oxide and methane emissions from denitrifying bioreactors with and without a soil cover

Brunton, Ann Marie

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https://hdl.handle.net/2142/116023 Copy

Description

Title

Nitrous oxide and methane emissions from denitrifying bioreactors with and without a soil cover

Author(s)

Brunton, Ann Marie

Issue Date

2022-05-17

Director of Research (if dissertation) or Advisor (if thesis)

• Christianson, Laura E
• Cooke, Richard A

Committee Member(s)

Zilles, Julie L

Department of Study

Engineering Administration

Discipline

Agricultural & Biological Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Denitrifying Bioreactor
• greenhouse gas
• nitrous oxide
• methane
• nitrate
• water quality

Abstract

Denitrifying woodchip bioreactors reduce nitrate loads in subsurface agricultural drainage water, thus reducing agriculture’s impact on water quality. However, bioreactors can emit the greenhouse gases nitrous oxide (N2O) and methane (CH4) as unwanted byproducts both through the bioreactor surface and as dissolved gas in the liquid outflow. The current United States Department of Agriculture design standard for denitrifying bioreactors allows flexibility as to whether a bioreactor is built with or without a soil cover, but it is unknown how greenhouse gases vary with or without a soil cover at the field-scale in real-world conditions. The objective of this study was to compare both surface and dissolved N2O and CH4 emissions at three full-scale bioreactors with a soil cover versus three without a soil cover in Illinois, USA to determine the impact of a soil cover on bioreactor greenhouse gas emissions. Each of the six bioreactors were monitored at least five times over March to August 2021 for: surface N2O and CH4 emissions; bioreactor flow rate; inflow and outflow dissolved N2O and CH4 and nitrate-nitrogen; and inflow and outflow temperature, dissolved oxygen (DO), and oxidation reduction potential. Hydraulic retention times varied widely between sites (means 1.8 to 21.6 h) but did not equally span the two treatments, preventing meaningful comparison of the covered vs. uncovered treatments and resolution of the stated objective; other trends outside of the two treatments were instead analyzed. Across all six sites, combined (surface and dissolved) mean nitrous oxide emissions (-1.57 to 14.5 mg N2O-N/m3-d) were 1-3 orders of magnitude lower than mean nitrate mass removal (0.291 to 2.97 g NO3-N/m3-d). Methane emissions (mean -1.16 to 412 mg CH4-C/m3-d) were nearly negligible from bioreactor surfaces, and like N2O, were mostly observed in the dissolved form. Methane and nitrous oxide approximately equally contributed to an impact on climate change, but methane was only released in noticeable quantities at half the bioreactors. Bioreactor #4 – No Cover consistently removed both N2O and CH4 due to low loading as well as possible young age impacts. Inducing low inflow DO levels or targeting a mid-range design HRT could mitigate climate change impacts from greenhouse gas emissions at subsurface drainage denitrifying bioreactors.

Graduation Semester

2022-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Ann Brunton

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