Ethanol production potential from AFEX™ and steam-exploded sugarcane residues for sugarcane biorefineries
Date
2018-05-04
Journal Title
Journal ISSN
Volume Title
Publisher
BioMed Central
Abstract
Background: Expanding biofuel markets are challenged by the need to meet future biofuel demands and mitigate
greenhouse gas emissions, while using domestically available feedstock sustainably. In the context of the sugar
industry, exploiting under-utilized cane leaf matter (CLM) in addition to surplus sugarcane bagasse as supplementary
feedstock for second-generation ethanol production has the potential to improve bioenergy yields per unit land. In
this study, the ethanol yields and processing bottlenecks of ammonia fibre expansion (AFEX™) and steam explosion
(StEx) as adopted technologies for pretreating sugarcane bagasse and CLM were experimentally measured and compared
for the first time.
Results: Ethanol yields between 249 and 256 kg Mg−1 raw dry biomass (RDM) were obtained with AFEX™-pretreated
sugarcane bagasse and CLM after high solids loading enzymatic hydrolysis and fermentation. In contrast, StEx-pretreated
sugarcane bagasse and CLM resulted in substantially lower ethanol yields that ranged between 162 and 203 kg Mg−1
RDM. The ethanol yields from StEx-treated sugarcane residues were limited by the aggregated effect of sugar degradation
during pretreatment, enzyme inhibition during enzymatic hydrolysis and microbial inhibition of S. cerevisiae 424A
(LNH-ST) during fermentation. However, relatively high enzyme dosages (> 20 mg g−1 glucan) were required irrespective
of pretreatment method to reach 75% carbohydrate conversion, even when optimal combinations of Cellic
® CTec3,
Cellic
® HTec3 and Pectinex Ultra-SP were used. Ethanol yields per hectare sugarcane cultivation area were estimated at
4496 and 3416 L ha−1 for biorefineries using AFEX™- or StEx-treated sugarcane residues, respectively.
Conclusions: AFEX™ proved to be a more effective pretreatment method for sugarcane residues relative to StEx
due to the higher fermentable sugar recovery and enzymatic hydrolysate fermentability after high solids loading
enzymatic hydrolysis and fermentation by S. cerevisiae 424A (LNH-ST). The identification of auxiliary enzyme activities,
adequate process integration and the use of robust xylose-fermenting ethanologens were identified as opportunities
to further improve ethanol yields from AFEX™- and StEx-treated sugarcane residues.
Description
CITATION: Mokomele, T., et al. 2018. Ethanol production potential from AFEX™ and steam-exploded sugarcane residues for sugarcane biorefineries. Biotechnology for Biofuels, 11:127, doi:10.1186/s13068-018-1130-z.
The original publication is available at https://biotechnologyforbiofuels.biomedcentral.com
The original publication is available at https://biotechnologyforbiofuels.biomedcentral.com
Keywords
Bagasse, Ethanol fuel, Biofuels, Sugarcane
Citation
Mokomele, T., et al. 2018. Ethanol production potential from AFEX™ and steam-exploded sugarcane residues for sugarcane biorefineries. Biotechnology for Biofuels, 11:127, doi:10.1186/s13068-018-1130-z