Anaerobic thermophilic fermentation for carboxylic acid production from in-storage air-lime-treated sugarcane bagasse.
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abstract
Wet storage and in situ lime pretreatment (50C, 1-atm air, 56days, excess lime loading of 0.3g Ca(OH)(2)/g dry biomass) of sugarcane bagasse (4,000g dry weight) was performed in a bench-scale pile pretreatment system. Under thermophilic conditions (55C, NH(4)HCO(3) buffer, methane inhibitors), air-lime-treated bagasse (80wt.%) and chicken manure (20wt.%) were anaerobically co-digested in 1-L rotary fermentors by a mixed culture of marine microorganisms (Galveston, TX). During four-stage countercurrent fermentation, the resulting carboxylic acids consisted of primarily acetate (average 87.7wt.%) and butyrate (average 9.0wt.%). The experimental fermentation trains had the highest yield (0.47g total acids/g volatile solids (VS) fed) and highest selectivity (0.79g total acids/g VS digested) at a total acid concentration of 28.3g/L, which is equivalent to an ethanol yield of 105.2gal/(tonne VS fed). Both high total acid concentrations (>44.7g/L) and high substrate conversions (>77.5%) are predicted for countercurrent fermentations of bagasse at commercial scale, allowing for an efficient conversion of air-lime-treated biomass to liquid transportation fuels and chemicals via the carboxylate platform.