Most academic research and commercial development efforts on renewable liquid fuels production have been focused on ethanol production via a three step route: chemical pretreatment of the biomass, enzymatic deconstruction of the pretreated biomass, and microbial fermentation of the hydrolyzed biomass to yield ethanol. However, this route cannot be applied economically to renewable feedstocks such as municipal solid waste streams that contain large quantities of non-carbohydrate materials. An alternative conversion route that is applicable to a wider range of biomass sources is gasification of the feedstock to produce synthesis gas (syngas) followed by direct fermentation of the syngas by specialized microbes to produce liquid fuels such as ethanol. While commercial development of syngas fermentation technology is underway, there remains many research challenges including improved understanding of metabolic pathways involved in syngas conversion, more detailed analysis of inhibitory compounds that result from biomass gasification, and optimization of syngas fermentation conditions to maximize fuel production.

To address these challenges, we are combining bioreactor experiments and metabolic modeling to develop improved fundamental understanding that facilitates process optimization of syngas bioconversion into alcohols such as ethanol and butanol. Our current research is focused on ethanol production with the bacterium Clostridium ljungdahlii using syngas derived by gasification of municipal solid waste (MSW). Ongoing work involves characterizing the effects of fermentation conditions on cellular metabolism using synthetic syngas that mimics MSW derived mixtures and developing a genome-scale model of cellular metabolism using the recently annotated genome and our fermentation data. Our longer term goal is to perform model-based bioreactor optimization to maximize alcohol production from syngas mixtures derived by gasification of MSW feedstocks.

Funding: ReCommunity Recycling

Student: Jin Chen (2nd year Ph.D. student)

Collaborator: Dingrong Bai (ReCommunity Recycling), Paul Dauenhauer (UMass)

Hybrid synthesis gas fermentation route (green) for conversion of renewable feedstocks into biofuels.