Abstract
Among the various agro-industrial by-products, sugar beet molasses produced by sugar refineries appear as a potential feedstock for ethanol production through yeast fermentation. A response surface methodology (RSM) was developed to better understand the effect of three process parameters (concentration of nutrient, yeast and initial sugar) on the ethanol productivity using diluted sugar beet molasses and Saccharomyces cerevisiae yeast. The first set of experiments performed at lab-scale indicated that the addition of 4 g/L of nutrient combined with a minimum of 0.2 g/L of yeast as well as a sugar concentration lower than 225 g/L was required to achieve high ethanol productivities (>15 g/L/d). The optimization allowed to considerably reduce the amount of yeast initially introduced in the fermentation substrate while still maximizing both ethanol productivity and yield process responses. Finally, scale-up assays were carried out in 7.5 and 100 L bioreactors using the optimal conditions: 150 g/L of initial sugar concentration, 0.27 g/L of yeast and 4 g/L of nutrient. Within 48 h of incubation, up to 65 g/L of ethanol were produced for both scales, corresponding to an average ethanol yield and sugar utilization rate of 82% and 85%, respectively. The results obtained in this study highlight the use of sugar beet molasses as a low-cost food residue for the sustainable production of bioethanol.
Highlights
Ethanol production was strongly affected by the three investigated process parameters, which resulted in different fermentation kinetics among the 16 experiments of the composite design coupled with response surface methodology (CCDRSM) (Figure 2)
The highest ethanol production of 92 g/L was observed when the sugar beet molasses was diluted to 225 g/L of initial sugars combined with the use of 0.6 g/L and 4.0 g/L of yeast and nutrient, respectively
To confirm that the CCD-response surface methodology (RSM) model can be used to make accurate process predictions, validation experiments were performed at lab-scale using 50 mL vials based on the results presented in the first part of this study
Summary
One of the main reasons related to the actual environmental issues is the high amount of greenhouse gases (GHG) continuously released into the atmosphere due to anthropogenic activities (industries, land use, transportation, etc.) [2]. In this context, the use of biofuels such as bioethanol has emerged as a sustainable alternative to fossil fuels due to numerous advantages, including reduced emission of GHG, hydrocarbons and nitrogen oxides during both bioethanol production and combustion [3]. Many countries have been adopting new policies to promote the use of biofuels, and the market perspectives are a 2-fold increase in Brazil and the USA and a 4-fold increase in China and EU by 2040 [4]
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