INNOVATIVE ANAEROBIC DIGESTION INVESTIGATION OF FATS, OILS, AND GREASE

Fats, oils, and grease (FOG) is a waste stream that has the potential to increase biogas production in anaerobic digestion. Triglycerides, glycerol esters of fatty acids, are the primary volatile component of FOG. Anaerobic digestion of triglycerides results in the end products methane gas, carbon dioxide and water.The components of FOG critical to methane gas production in the anaerobic digestion process are long chain fatty acids (LCFAs), composed of C8 to C20 carbon chains, and can be monounsaturated or polyunsaturated. LCFAs in FOG may cause digester instability. Many researchers using various LCFAs as feed for anaerobic treatment processes have observed inhibition of methanogenesis and toxicity to the anaerobic microorganisms integral to the digestion process.Prior LCFA degradability and toxicity studies have used a wide variety of methods, and have produced conflicting results on the impacts of LCFAs on FOG digestion. The primary objective of the East Bay Municipal Utility District's (EBMUD) process optimization study, was to determine the upper limit of FOG loading as a percent of total feed for full-scale anaerobic digestion at thermophilic and mesophilic temperatures, and to understand the inhibitory components and mechanisms that limit FOG digestion, with a specific focus on LCFAs.