Date of Award
Master of Science (MS)
Environmental Engineering and Earth Science
Dr. Sudeep Popat
Dr. David Freedman
Dr. David Ladner
Various industries produce fats, oils, and greases (FOG). These hydrophobic compounds cause issues in municipal wastewater collection and treatment systems. Anaerobic co-digestion is an effective way to treat FOG and presents an opportunity to produce more significant quantities of biogas. However, many microorganisms are sensitive to the degradation products like long-chain fatty acids (LCFAs). Palmitic acid is the most prevalent LCFA in anaerobic co-digestion of FOG and wastewater. Sytrophomonas is a β-oxidizer able to break down palmitic acid. Palmitic acid is known to feed and inhibit Syntrophomonas growth and methanogenesis. The objectives of this investigation are: To determine if Syntrophomonas abundance increases in response to palmitic acid addition and to determine if there are palmitic acid concentrations that led to inhibition or lag in the growth of Syntrophomonas.
All three studies in this investigation co-digested various percentages of inoculum of anaerobic digester sludge collected from Renewable Water Resources (ReWA), and different amounts of palmitic acid were conducted. The purpose was to use palmitic acid to find an optimal concentration for Syntrophomonas growth and a concentration where growth was inhibited. Multiple batch growth tests were conducted with anaerobic assay bottles. The bottles were measured daily for methane, long-chain fatty acids, and DNA throughout the experiments. Increasing percentages of palmitic acid corresponded to a delay in and a slightly slower methane production rate.
In the first study, the batch growth bottles had 2 mM palmitic acid and various Inoculum amounts. The 5% inoculum had lower methane yields than the 10% and 20%, but the higher percentages had a lag time. Palmitic acid degradation also showed similar trends where 5% had little to no degradation and Syntrophomonas growth, and 10% and 20% of inoculum had palmitic acid degradation and Syntrophomonas growth. The following two studies investigated 10% and 20% inoculum with different palmitic acid concentrations (0 mM, 2 mM,4 mM, and 6 mM) to explore Syntrophomnas growth rates. In study 2, inhibition occurred with higher amounts of palmitic acid and had a slower growth rate as the palmitic acid concentration increased. In study 3, the same pattern happened but with less inhibition. In these patterns, the palmitic acid concentration was high enough to delay the onset of methanogenesis and the growth of Syntrophomonas. The increased abundance of Synthrophomonas likely aided the β-oxidation of palmitic acid to acetate and hydrogen. The results of this study support the hypothesis that palmitic acid has some inhibition in terms of Syntrophomonas growth depending on concentration. Furthermore, the more Syntrophormonas present in anaerobic digestion, the more methane will be produced due to the β-oxidation of LCFAs to acetate via a syntrophic partnership of proton-reducing acetogenic bacteria.
Kerr, Clancy, "Evaluating the Effect of Palmitic Acid Concentration on Growth and inhibition of Syntrophomonas sp." (2023). All Theses. 4078.
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