Denitrifying bioreactor performance linkages with wood media type, moisture exposure, and bacterial vs. fungal activity

Nonpoint-source agricultural nutrient pollution is a significant concern despite continued mitigation efforts. The denitrifying bioreactor is a conservation practice typically implemented at the edge-of-field to remove excess nitrate (NO3-) from agricultural drainage water. Woodchips are the most commonly used media in this type of bioreactor. Denitrifying microorganisms utilize carbon in the wood as their energy source to reduce NO3- in water to nitrogen gases. The effects of wood type, age, and moisture conditions were evaluated to understand how those factors affect: possible negative environmental tradeoffs of bioreactors, bacterial and fungal denitrification; wood degradation and changes in woodchip nutrient content; and overall denitrification performance of the bioreactors. A bioreactor mesocosm leaching test using oak (Quercus rubra), Emerald Ash Borer (EAB)-killed ash (Fraxinus spp. L.), and a generic hardwood blend showed that oak initially leached higher concentrations of tannic acid, true color, and chemical oxygen demand, but after 84 d of flushing, the significant differences in leached concentrations among the three wood types were eliminated. Field bioreactor outflow from five sites and agricultural stream tannic acid concentrations provided context to the observed concentrations in the lab experiment. Measured field bioreactor outflows did not exceed 12 mg tannic acid/L. After 84 d of initial flushing, the oak, ash and mixed hard wood leachate tannic acid concentrations fell within the concentrations observed in collected stream samples. The high tannin oak or EAB -killed ash wood had no negative effect on NO3- removal performance suggesting that those readily available wood sources could be used as bioreactor media with proper precautions such as pre-flushing and treating the EAB larvae. An evaluation of woodchip age and moisture exposure using woodchips harvested from a field-scale bioreactor showed that both bacterial and fungal denitrification occurs in bioreactors. However, the NO3- removal was predominantly performed by bacteria rather than fungi, regardless of woodchip saturation or age. The laboratory assays evaluating the field bioreactor woodchips showed that the bacterial and fungal NO3- removal rates increased with bioreactor age across 47 months. Woodchips exposed to more aerobic than anaerobic conditions lost mass and had their carbon: nitrogen ratio decline faster. The knowledge of wood constituents and their effects on NO3- removal, microorganisms responsible for denitrification, negative environmental tradeoffs, and changes in woodchip properties will help improve bioreactor design and management.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Crop Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2022

Author dc:creator

• Wickramarathne, Niranga M

Contributors dc:contributor

• Christianson, Laura E
• Zilles, Julie L
• Cooke, Richard A
• Davidson, Paul C

• Bioreactors
• fungal denitrification
• bacterial denitrification
• wood media longevity
• tannic acid
• emerald ash borer
• oak wood
• ash wood

Statement dc:rights

• Copy right 2022 Niranga M. Wickramarathne

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/115903

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F115903