Autohydrolysis pretreatment of castor plant pruning residues to enhance enzymatic digestibility and bioethanol production

Castor plant is used commonly for oil extraction and biodiesel synthesis. However, the residues during pruning are not being used effectively. These residues have the potential to be used as feedstock to produce bioethanol and other by-products. The present work assessed the eco-friendly autohydrolysis pretreatment of castor plant pruning residues at different severity factors (R0), applying a range of temperatures from 100 °C to 200 °C. The hydrolysis of pretreated solids was carried out using a commercial cellulases complex at different solid and enzyme loadings. The enzymatic hydrolysate with a higher glucose concentration was further subjected to fermentation using Saccharomyces cerevisiae ATCC 4126. The results showed an efficient xylan hydrolysis (77.5%) and a preservation of glucan up to 83% in the solids pretreated at an R0 of 5.78. The enzymatic hydrolysis of the pretreated solids at an R0 of 5.78 showed a glucose release of 2.9-fold higher than non-pretreated material. In the hydrolysate fermentation, a maximum ethanol production of 50.5 g/L was achieved (equivalent to 6.4% v/v), corresponding to a conversion efficiency of 98% and a biomass-to-ethanol conversion yield of 93.0 g of ethanol per kilogram of feedstock.

Global Warming Potential of Biomass-to-Ethanol: Review and Sensitivity Analysis through a Case Study

In Europe, ethanol is blended with gasoline fuel in 5 or 10% volume (E5 or E10). In USA the blend is 15% in volume (E15) and there are also pumps that provide E85. In Brazil, the conventional gasoline is E27 and there are pumps that offer E100, due to the growing market of flex fuel vehicles. Bioethanol production is usually by means of biological conversion of several biomass feedstocks (first generation sugar cane in Brazil, corn in the USA, sugar beet in Europe, or second-generation bagasse of sugarcane or lignocellulosic materials from crop wastes). The environmental sustainability of the bioethanol is usually measured by the global warming potential metric (GWP in CO2eq), 100 years time horizon. Reviewed values could range from 0.31 to 5.55 gCO2eq/LETOH. A biomass-to-ethanol industrial scenario was used to evaluate the impact of methodological choices on CO2eq: conventional versus dynamic Life Cycle Assessment; different impact assessment methods (TRACI, IPCC, ILCD, IMPACT, EDIP, and CML); electricity mix of the geographical region/country for different factory locations; differences in CO2eq factor for CH4 and N2O due to updates in Intergovernmental Panel on Climate Change (IPCC) reports (5 reports so far), different factory operational lifetimes and future improved productivities. Results showed that the electricity mix (factory location) and land use are the factors that have the greatest effect (up to 800% deviation). The use of the CO2 equivalency factors stated in different IPCC reports has the least influence (less than 3%). The consideration of the biogenic emissions (uptake at agricultural stage and release at the fermentation stage) and different allocation methods is also influential, and each can make values vary by 250%.

Woody Biomass Processing and Rural Regional Development

The authors report on the economic impacts of introducing woody biomass processing in an economically distressed, but heavily forested Central Appalachian U.S. region. Woody biomass is a readily available unconventional energy source that has the potential to boost the rural region’s economy. They use a static regional computable general equilibrium model to assess long-run economic impacts of two woody biomass processing production pathways of biomass to ethanol through fermentation and biomass to biofuel through fast pyrolysis. While the 232 to 370 jobs and $13 million to $21 million income might seem small relative to the multicounty region, the localized impact on the county in which the facility would be sited, even for the direct jobs and income impacts, would be much more substantial. The authors conclude that woody biomass processing is a viable economic development option for the study area and similar rural regions.