Waste-to-fuel technologies for the bioconversion of carrot discards into biobutanol

Carrot discard was evaluated as a raw material for acetone-butanol-ethanol (ABE) fermentation. Different strategies based on hydrothermal pretreatment and/or enzymatic hydrolysis were compared for biobutanol production from carrot discard pulp. In addition, the use of different types of enzymes and diverse enzyme mixtures were evaluated. In this way, total sugar recoveries of up to 76%, and butanol and ABE concentrations of 7.4 and 11.5 g/L, respectively (74 g butanol and 115 g ABE/kg carrot pulp), were achieved when the carrot discard pulp was enzymatically hydrolyzed, without pretreatment, using a mixture of enzymes of Cellic CTec2 and Viscozyme L at a dosage of 0.1 and 0.2 g/g, respectively. When a hydrothermal pretreatment was applied, a total sugar recovery of 88%, 6.9 g/L butanol and 10.1 g/L ABE (69 g butanol and 101 g ABE/kg carrot pulp) were attained using the same mixture of enzymes. In this way, no hydrothermal pretreatment would be necessary to produce ABE from carrot discard, which is very interesting for the profitability of the process. Furthermore, the carrot discard juice yielded 6.4 and 9 g/L butanol and ABE, respectively, showing that all the carrot discards could be used for ABE production.