New paradigms for low-cost processing of cellulosic biomass

C. thermocellum was compared to industry standard fungal cellulase and found to be markedly more effective at achieving high total carbohydrate solubilization for a broad range of feedstocks and conditions.  As an alternative to conventional pretreatment, we are investigating physical disruption once fermentation is initiated, termed cotreatment, with initial exploration using continuous ball milling during thermophilic fermentation.  First-of-a-kind data and analysis supporting this concept will be presented. Findings include: a) milling at intensities sufficient to allow solubilization comparable to conventional pretreatment has little or no effect on soluble sugar fermentation by C thermocellum but completely halts fermentation by yeast, and b) energy requirements for cotreatment-enhanced thermophilic fermentation are expected to be radically lower than for milling as a pretreatment for subsequent solubilization using fungal cellulase.  

Taking advantage of the capability of thermophilic cellulolytic anaerobes to ferment cellulosic biomass without added enzymes requires that metabolic engineering tools be developed and applied pursuant to bringing product yields and titers to industrially acceptable levels.  Progress in engineering thermophilic microbes for consolidated bioprocessing (CBP) will be described, including characterization of a high-performing ethanol pathway in Thermoanaerobacterium saccharolyticum, and efforts to transfer this pathway to Clostridium thermocellum. 

Process analysis will be presented supporting the potential for biomass conversion at radically lower cost, particularly at small scale, by combining cotreatment, thermophilic fermentation, and configurations that minimize the cost of outside-battery-limit components.   Advantages of colocating cotreatment-enhanced thermophilic conversion colocated at an existing ethanol plant, rather than a stand-alone new plant, will also be addressed.