(752f) Refining the Concept of Integrating Anaerobic-Aerobic Microbial Systems to Produce Chemicals and Lipids for Fuels

An emerging paradigm in the creation of sustainable chemical-manufacturing processes is the capture and utilization of residual valuable substances in waste streams through the transformation of existing treatment facilities such as wastewater treatment plants into urban-based biorefineries. One of the recent technologies developed based on this vision is the accumulation of lipids by activated sludge from wastewater treatment plants. Lipids from activated sludge have been shown as a promising feedstock in biodiesel production. Feeding activated sludge with high amount of carbon sources such as sugars establishes high carbon-to-nitrogen ratio that triggers the increase of lipid content of the sludge after certain aerobic incubation period. The enhanced sludge can then be processed for lipid extraction and biodiesel production.

The commercialization of the aerobic lipid accumulation by sludge, however, is challenged by the relatively high cost of the typical monosaccharide substrates such as glucose and xylose. In this study, the feasibility of utilizing as substrates volatile fatty acids (VFAs), such as acetic acid, propionic acid and butyric acid produced from the anaerobic digestion of cellulose was examined.

This paper will show the results of evaluating integrated biomass anaerobic digestion-aerobic lipid accumulation. Kinetic studies on the digestion of cellulose by wastewater anaerobic sludge and aerobic lipid accumulation from volatile fatty acids (VFAs) by activated sludge were conducted.  Kinetic data were fitted to mechanistic models, which were then used for the simulation of the integrated processes.  Simulation results will be presented. Solution methods used to improve the performance of the integrated system will also be discussed. Since valuable substances other than lipids have been detected in the product streams of laboratory experiment reactions, these will be considered in the discussion of the economics of the integrated processes.

The envisioned integrated process is the production of lipids from lignocellulosic biomass while minimizing energy inputs to deconstruct the latter to yield assimilable carbon sources. An anaerobic microbial system favors high feedstock-to-extracellular products mass flux while an aerobic microbial system favors high substrate-to-intracellular products mass flux. These inherent characteristics make the two systems favorable for integration to accomplish the objective of transforming lignocellulosics to biodiesel and biogas. Furthermore, the energy input in undefined mixed microbial cultures such as the anaerobic sludge and activated sludge could be minimized because of the sufficiency of operating in non-sterile conditions that does not require high heat input.