Date of Award
Master of Science (MS)
Environmental Engineering and Earth Science
Due to increased methane yields, anaerobic co-digestion of fats, oils, and grease (FOG) and municipal solids is an attractive process to employ at water resource recovery facilities (WRRFs). For many practitioners in the industry, the risks associated with anaerobic co-digestion of FOG have overshadowed the many benefits. In recent years, much effort has been given to understanding the chemical and microbial aspects of achieving stable co-digestion of FOG. To date, no full-scale studies have been conducted to understand how the current research applies to FOG co-digestion at scale. To fill this gap within the literature, two 1.36-million-gallon digesters receiving primary solids, thickened waste activated solids, and FOG were sampled during a 10-month period. COD and volatile solids (VS) concentrations were measured weekly for influent and effluent steams. Concentrations of short chain fatty acids were measured weekly within each digester and concentrations of long chain fatty acids were measured weekly within each digester and in the FOG holding tank. Methane content of biogas was measured once per week. qPCR targeting the genus Syntrophomonas and 16S rRNA gene sequencing was performed on digester biomass twice per month and once per month, respectively. FOG loading averaged 10.3 and 13.8 % of VS and COD loading respectively and reached as high as 24.5 and 35 % of VS and COD loading respectively. Concentration of acetate, pH, alkalinity, and methane content of the biogas all stayed well within values that indicate stable and healthy anaerobic digestion. The microbial community was able to keep LCFA concentrations within the digester below inhibitory levels throughout the study in spite of fluctuations within the mass rate of LCFAs delivered to the digesters. A strong positive correlation was found between % VS destroyed and kg of FOG VS fed per day indicating that FOG behaves as an easily degradable substrate and enhances % VS destruction. Relative abundance of Rikenellaceae RC9 gut group, Cloacimonadaceae W5, Synergistaceae uncultured, and Methanofastidiosum were all enriched when intermediate LCFA concentrations remained low. Relative abundance of Methanospirillum and Smithella were enriched when LCFA concentrations increased. Increases in the concentration of LCFA within the digesters caused sharp changes to 16S rRNA gene copies of Syntrophomonas, while increases to LCFA mass rate resulted in lower response times from Syntrophomonas.
Solon, Thomas, "Performance of Full-Scale Anaerobic Co-Digestion of FOG and Municipal Solids with an Emphasis on Syntrophomonas Populations" (2022). All Theses. 3918.