Date of Award
Master of Science (MS)
Environmental Engineering and Earth Science
Dr. Sudeep Popat
Dr. Barbara Campbell
Dr. Kevin Finneran
Fats, oils and greases are produced from a variety of industries, including animal rendering operations, vegetable oil processing plants and the hospitality industry. These hydrophobic, COD-rich compounds are known to cause issues in municipal wastewater collection and treatment systems. Anaerobic co-digestion has been shown to be an effective way to treat FOG and presents an opportunity to produce greater quantities of biogas. However, many microorganisms are sensitive to the degradation products of FOG, including long and short chain fatty acids. Two studies were performed to address potential inhibitory effects of both.
The first study co-digested various percentages of FOG with primary sludge, waste activated sludge and anaerobic digester sludge collected from Fort Wayne Hill Water Resource Center (FWHWRC). The purpose was to use FOG specific to FWHWRC to determine an optimal concentration of FOG yielding the greatest amount of methane. This BMP assay bottles were measured daily for methane, every five days for short and long chain fatty acids throughout the 50-day experiment. Day zero and day fifty DNA samples were collected. Increasing percentage of FOG corresponded to a delay in and a slightly slower rate of methane production. BMP bottles with 15% FOG had similar methane yield as 10% FOG, but with a slower ramp up time. BMP bottles with 20% FOG took longer than 15% FOG bottles and did not produce as much methane by day 50, indicating some inhibition within the anaerobic digestion metabolic pathway.
The second study looked more closely at inhibitory LCFAs and SCFAs; palmitic acid and acetic acid. Few other studies have looked at these two fatty acids’ direct effect on methane production. This BMP study involved the supplementation of sodium palmitate, sodium acetate or both to anaerobic batch bottles given anaerobic minimal media and anaerobic digester sludge. Methane, short and long chain fatty acid, DNA, and RNA samples were collected throughout the 45-day experiment. It was determined that 10 mM sodium palmitate was enough to delay exponential methane production by as much as 45 days. Five mM of palmitic acid alone was not enough to inhibit or delay methanogenesis. The addition of acetate delayed the onset of exponential methane production likely by stalling the β-oxidation reaction of LCFAs to acetate and hydrogen. Ten mM of palmitic acid alone prevented exponential methanogenesis. Methanobacterium, a hydrogenotrophic, slow-growing methanogen, was the most abundant genus and likely the primary methane producer. The palmitic acid concentration was high enough to delay the onset of methanogenesis. The increased abundance of Synthrophomonas likely aided in the β-oxidation of palmitic acid to acetate and hydrogen. Methanobacterium and Methanosarcina were the dominant archaeal genera during exponential methane production. The results of this study support the hypothesis that there is some inhibition by LCFAs upstream of methanogenesis and it is likely within β-oxidizing bacterial communities.
Spier Camposano, Emmaline, "Effect of Long and Short Chain Fatty Acids on Methane Yield and Microbial Community Composition in Anaerobic Co-digestion" (2021). All Theses. 3667.