Bioengineering approaches to high-solids cellulose fermentation for biofuel production

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The long-term objective of the research is to develop a semi-continuous, fed-batch fermentation process using high concentrations (10% or greater) of cellulose as the substrate for biofuels (ethanol and hydrogen) production. Our model organism, Clostridium thermocellum, is a gram-positive, thermophilic, acetogenic, anaerobe that can utilize cellulose as a sole carbon source and synthesizes ethanol, acetate, and other organic acids via a mixed fermentation metabolism, with the concomitant release of hydrogen (H2) and carbon dioxide (CO2). This research will focus on development of the high solids fermentation process. Biofuel production from cellulose fermentation presents a number of unique biological and engineering challenges, such as: i) how to move insoluble substrate at high concentration into, and mix the substrate within, a bioreactor; ii) how to quantify conversion of the substrate from long polymers of glucose to oligocellulodextrins and/or soluble sugars (cellobiose and glucose); iii) how to quantify cell growth on an insoluble substrate; iv) how to recover the ethanol produced from the vapour phase of the fermentation reaction; and v) how to purify, capture, and store the hydrogen produced. The goal of this proposed NSERC Discovery grant is to build upon the progress that we have made and address these challenges. The short-term objectives of this proposal are to: 1) develop a reliable and accurate method to quantify rates of substrate conversion during cellulose fermentation; 2) quantify cell growth on an insoluble substrate; and 3) integrate and validate a continuous, real-time monitoring system for metabolites during cellulose fermentation. This research bridges the gap between science and engineering to develop a Consolidated Bioprocessing approach for biofuel production using cellulose as a substrate for fermentation. Consolidated Bioprocessing of cellulosic substrates offers significant potential as a viable process for next generation biofuel production by reducing upstream processing costs.