| Pretreatment, enzyme production, enzymatic hydrolysis, hexose and pentose fermentation are the most costly and least understood technologies for producing ethanol from cellulose. Combining biologically mediated processes into one reactor, termed consolidated bioprocessing (CBP), may greatly reduce the cost of ethanol production.; Paper sludge, a cellulose rich industrial waste, was highly reactive in enzymatic hydrolysis. Simultaneous saccharification and fermentation (SSF) using Saccharomyces cerevisiae and Trichoderma reesei cellulase achieved rapid and near full conversion of paper sludge at up to 35 and 95 g/L cellulose feed, respectively.; Bagasse, aspen chips and hardwood flour were pretreated with compressed liquid hot water (LHW). All achieved high conversion at moderate rates in batch SSF. The hydrolyzate from LHW pretreated bagasse was only slightly inhibitory to S. cerevisiae growing in batch culture on glucose.; A defined medium supported growth of Clostridium thermocellum at 50 g/L feed in continuous culture on cellobiose and in sequencing batch (SBR) on Avicel. Continuous culture of Avicel gave slower growth rates at elevated substrate ({dollar}sim{dollar}40 g/L) concentrations.; At low concentrations ({dollar}sim{dollar}10 g cellulose/L), paper sludge is readily converted in batch, SBR or continuous culture by C. thermocellum. C. thermocellum cocultured with Thermoanaerobacter thermosaccharolyticum produced slightly higher ethanol selectivities. In SBR, C. thermocellum achieved 90% conversion of paper sludge in 24 hours at 10 g/L feed. Conversion required 48 hours at 20 g/L feed. At higher concentrations, conversion did not reach 90%. At higher feed concentrations, conversion was generally slower or incomplete.; Experiments suggest that C. thermocellum releases a soluble inhibitor at the end of batch growth at high substrate concentrations. The inhibitor could be inactivated by filtering through a 0.2{dollar}mu{dollar}m polypropylene filter.; A proposed model describes the allocation of cellular resources between cell propagation and production of cellulase. The model predicts that an optimal allocation exists and that high processing rates and yields are possible with CBP, especially at high cellulase specific activities. Experiments verified that at low substrate concentrations the model approach is valid for describing allocation, although the allocation also appears to bear a qualitative differentiation. |
