The main objective for this thesis was to develop techno-economic modeling tools to analyze two bioprocessing systems: anaerobic digestion and industrial fermentation. While both of these processes can be used to produce products that ultimately offset fossil fuels, there are fundamental differences between each process. Anaerobic digestion is a mixed culture process used for waste treatment - it uses a feedstock of low or sometimes negative value. In contrast, industrial fermentation is a pure culture process typically used to create high value products, requiring relatively expensive feedstocks and typically higher-technology infrastructure to support. Understanding the cost structures of different bioprocesses helps engineers and scientists identify critical variables that should be targeted for reducing production costs. This thesis is prepared in the journal paper format and includes two papers that have been prepared for submission to a journal.

The objective for the first paper in this thesis was to develop a model to analyze farm-scale anaerobic digestion. Anaerobic digestion is a biological process that can be used to treat animal waste, producing biogas and a nutrient-rich digestate. A spreadsheet model was developed to analyze economic and technical barriers to this technology, using operation size as the primary input and the cost for producing methane as the primary output. Trends in the methane cost ratio, or the ratio of the production cost for methane to the market value of natural gas, as a function of different process variables were evaluated, and recommendations for improving deployment rates were discussed. Results showed that moderate reductions in the interest rate are capable of making 1000-cow digesters economically feasible if high carbon credits values, high natural gas prices, and low gas clean-up costs can be achieved; however, if carbon credit values are low as they currently are, more extreme modifications to the digester cost and interest rate, combined with increases in digester life and/or natural gas prices are required for smaller dairies to break-even when using anaerobic digestion.

The objective for the second paper was to develop a model to analyze the cost structure of industrial fermentation processes for producing biorenewable chemicals. As metabolic engineers develop improved microbial strains for industrial fermentation, understanding the tradeoffs between different kinetic parameters on the production cost is vital. A spreadsheet model was developed to provide an order-of-magnitude estimate of chemical production cost based on kinetic and operating parameters. Results showed that production cost is most sensitive to yield, fraction of product in the biomass, and substrate concentration. Feedstock cost makes up the largest portion of the production cost except under the most pessimistic fermentation conditions. Minimizing fermentation costs is critical to making biorenewable chemicals cost competitive with their well-established petroleum-derived competitors.