Fermentation of Sugarcane Bagasse and Chicken Manure to Calcium Carboxylates under Thermophilic Conditions

Sugarcane bagasse and chicken manure were anaerobically fermented to carboxylic acids using a mixed culture of marine microorganisms at 55 °C. Using the MixAlco process— an example of consolidated bioprocessing— the resulting carboxylate salts can be converted to mixed alcohol fuels or gasoline. To enhance digestibility, sugarcane bagasse was lime pretreated with 0.1 g Ca(OH)₂/g dry biomass at 100 °C for 2 h. Four-stage countercurrent fermentation of 80% sugarcane bagasse/20% chicken manure was performed at various volatile solids (VS) loading rates and liquid residence times. Calcium carbonate was used as a buffer during fermentation. The highest acid productivity of 0.79 g/(L day) occurred at a total acid concentration of 21.5 g/L. The highest conversion (0.59 g VS digested/g VS fed) and yield (0.18 g total acids/g VS fed) occurred at a total acid concentration of 15.5 g/L. The continuum particle distribution model (CPDM) predicted the experimental total acid concentrations and conversions at an average error of 10.14% and 12.68%, respectively. CPDM optimizations show that high conversion (>80%) and total acid concentration of 21.3 g/L are possible with 300 g substrate/(L liquid), 30 days liquid residence time, and 3 g/(L day) solid loading rate. Thermophilic fermentation has a higher acetate content (∼63 wt%) than mesophilic fermentation (∼39 wt%).