Enhanced fermentation of switchgrass by Clostridium thermocellum via continuous ball-milling

We are exploring milling of partially-fermented solids, termed cotreatment, as an alternative to thermochemical pretreatment in order to enhance biomass solubilization by thermophilic bacteria. Results are reported here for batch fermentation of senescent switchgrass with and without continuous ball-milling throughout fermentation. Total carbohydrate solubilization after 5 days increased from of 41% without milling to 83% with ball milling. Milling at the same intensity had little or no effect on the rate of cellobiose consumption by C. thermocellum, but significantly inhibited glucose consumption by yeast. The different results observed in these soluble substrate controls is taken to be an indication of the greater resistance to mechanical disruption, and greater opportunity for application of cotreatment, for processing using gram-positive bacteria as compared to yeast. Analysis will be presented supporting the expectation that energy requirements for cotreatment-enhanced thermophilic fermentation will be far lower than for milling of unreacted solids prior to solubilization using fungal cellulase.