Thesis
Assessment of biomethane potential and reactor foaming during anaerobic co-digestion of organics
University of Iowa
Master of Science (MS), University of Iowa
Spring 2022
DOI: 10.25820/etd.006471
Abstract
Process stability is an ongoing difficulty in anaerobic digestion due to the interdependent biochemical processes that convert organic wastes to methane-rich biogas. In this study we investigated excessive foaming at a rural Water Resource Recovery Facility that co-digests mixed high strength organic wastes (HSW) (COD > 100,000 mg/L). Circumstances required a disproportionate use of HSW feedstock in 2020, which triggered excessive foaming and digester overflowing (“foam-over”). Limited data on the HSW and its impacts on the digester conditions made targeted mitigation difficult. To assist, we developed a predictive model of the facility’s dual mesophilic digesters. Composition and operational data were used to calibrate the model to investigate the underlying triggers for the foaming. Our analysis suggested that the foam-over events were caused by synergetic interactions between VS loading above 0.15 lb-VS/ft3/day, enhanced biogas generation from high (≥ 50%) HSW contributions, and low residence times. We then conducted a series of biomethane potential tests on the HSW to investigate potential toxicity. The HSW did not exhibit toxicity but instead bolstered biogas production and enhanced digester nutrient content. Since the HSW is frequently used as the predominant feedstock, understanding how the interactions between the HSW, foaming, and the overall digester condition could enable targeted strategies for improving process stability.
Details
- Title: Subtitle
- Assessment of biomethane potential and reactor foaming during anaerobic co-digestion of organics
- Creators
- Alexes S. Garrett
- Contributors
- Craig Just (Advisor)Gregory LeFevre (Committee Member)Timothy E. Mattes (Committee Member)
- Resource Type
- Thesis
- Degree Awarded
- Master of Science (MS), University of Iowa
- Degree in
- Civil and Environmental Engineering
- Date degree season
- Spring 2022
- Publisher
- University of Iowa
- DOI
- 10.25820/etd.006471
- Number of pages
- x, 48 pages
- Copyright
- Copyright 2022 Alexes S. Garrett
- Language
- English
- Description illustrations
- illustrations (some color)
- Description bibliographic
- Includes bibliographical references (pages 40-41).
- Public Abstract (ETD)
Anaerobic digestion, the degradation of wastes in the absence of oxygen, is a tried-and-true method of diverting wastes from landfills and converting them into useful byproducts like fertilizer and methane. However, anaerobic digestion requires maintaining a delicate balance between the native bacteria and the surrounding environment to avoid disrupting their function and stopping the digestion process. This is known as a reactor upset, or failure, and can take months to recover from. With the time commitment of start-up and expense of using this technology, it is important to maintain a stable digestion process to avoid additional costs for cleaning out and restarting the digester. In this study, we partnered with a rural Water Resource Recovery Facility to investigate issues with their digesters overflowing from increased high strength waste (HSW) digestion. To do this, we developed a model to help assess the condition of their digesters and the factors that contributed to the overflowing. We also ran biomethane potential tests to investigate the potential for excess HSW to trigger an upset and its influence on digester performance.
- Academic Unit
- Civil and Environmental Engineering
- Record Identifier
- 9984271453602771
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