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Harahap Dissertation5.01 MB
Embargoed Access, Embargo ends: 03/19/2027
Dissertation
Microbial Chain Elongation for Production of Medium Chain Carboxylic Acid from Wet Organic Waste
Washington State University
Doctor of Philosophy (PhD), Washington State University
12/2024
DOI:
https://doi.org/10.7273/000007248
Abstract
Microbial chain elongation is a biochemical process that converts lower-value chemicals such as ethanol and short chain carboxylic acids (SCCAs) into higher-value medium chain carboxylic acids (MCCAs). These MCCAs are derived from low-cost substrates, such as waste materials, and have lower solubility in water, making them easier to recover, and more suitable as precursors for sustainable aviation fuels (SAF) compared to ethanol and SCCAs. This study introduced an economically attractive process named AAD-CE, a sequential-arrested anaerobic digestion (AAD) followed by chain elongation (CE) using green waste for MCCA production. The primary objective was to develop and optimize microbial inoculum and CE conditions for efficient MCCA production, particularly caproic acid, from ethanol and SCCAs serving as electron donor (ED) and electron acceptor (EA), respectively, present in AAD effluent. The effluent was rich in acetic acid and butyric acid, contained low concentration of propionic acid, and lacked methanogenic activity, conditions ideal specifically for caproic acid production. The CE study revealed that the addition of ethanol shifted the microbial community in the AAD effluent, with Sporanaerobacter (23.2%) and Clostridium sensu stricto 12 (9.1%), MCCA-producing microorganisms, becoming dominant. After several enrichment cycles using ethanol
and acetate, the culture was further dominated by Clostridium sensu stricto 12 (53.1%), demonstrating this microorganism's stability during CE with ethanol and acetate. Compared to pure Clostridium kluyveri, the mixed culture exhibited greater resilience to high ethanol and acetate concentrations in AAD effluent. In batch fermentation with gradual ethanol addition (3 g/L/day), the culture achieved a maximum caproic acid yield of 13.4 g/L at 37 °C and pH 7.2, with an inoculum concentration of 15%. The downstream process analysis revealed that reactive extraction is a more cost-effective method for recovering protonated caproic acid compared to adsorption. In addition to AAD, acetate, substrate for CE, can also be produced by Moorella thermoacetica through gas fermentation using syngas derived from recalcitrant organic waste. This study showed that the adjustment of syngas composition was another strategy to optimize M. thermoacetica performance to produce acetic acid, instead of adding yeast extract increasing operational cost.
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Details
- Title
- Microbial Chain Elongation for Production of Medium Chain Carboxylic Acid from Wet Organic Waste
- Creators
- Budi Mandra Harahap
- Contributors
- Birgitte K Ahring (Chair)Hanwu Lei (Committee Member)Manuel Garcia-Perez (Committee Member)Stephen J Callister (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Department of Biological Systems Engineering
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 289
- Identifiers
- 99901195630401842
- Language
- English
- Resource Type
- Dissertation