(812d) Integration of Anaerobic Digestion of Cellulose Into Lipid Accumulation By a Mixed Microbial Consortium

Although lipids from enhanced activated sludge has been shown as a promising feedstock in biodiesel production, the relatively high cost of the fermentation carbon source, which is commonly glucose and/or xylose, creates challenges impacting broad commercialization. In this study, the feasibility of utilizing the volatile fatty acids (VFAs) produced from the anaerobic digestion of cellulose as substrates in the aerobic lipid accumulation by return activated sludge (RAS) was examined in 5-L bioreactors. Experimental results show that batch anaerobic digestion of cellulose can produce significant amounts of VFAs (acetic, propionic, and butyric acids) and biogas.  Additionally, the lipids in RAS increased by 44% through fed-batch feeding of glucose (60 g/L) and subsequently of VFAs (18 g/L; ratio of 6g-acetic:1g-propionic:3g-butyric) . These results suggested the need to use methanogen inhibitors, and variation of operational parameters to reduce biogas formation, and consequently, increase VFAs production.  Experiments to show the impact of other initial VFAs concentrations and ratios on lipid accumulation by RAS will be described during the presentation.  Integration of the anaerobic digestion and the lipid accumulation stages in a continuous process will be simulated using appropriate kinetic models.  Modeling results will be validated with experimental data.  The envisioned process is the production of lipids from lignocellulose, while minimizing energy inputs to deconstruct the latter to yield lower molecular weight and readily assimilable carbon sources (i.e., monosaccharide sugars and VFAs).  Sludges from wastewater treatment facilities could be transported to a centralized facility where lignocellulosic sources are transformed into VFAs for lipid accumulation by RAS, feedstock for specialty chemicals, and biogas.  Some of the energy requirements for the aerobic process could be provided by the generated biogas.