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. 2023 Dec;14(1):228-244.
doi: 10.1080/21655979.2023.2234135.

Optimization of energy recovery efficiency from sweet sorghum stems by ethanol and methane fermentation processes coupling

Bakari Hamadou  1   2   3 , Djomdi Djomdi  3 , Ruben Zieba Falama  1   4 , Roger Djouldé Darnan  3 , Fabrice Audonnet  2 , Pierre Fontanille  2 , Cedric Delattre  2 , Guillaume Pierre  2 , Pascal Dubessay  2 , Philippe Michaud  2 , Gwendoline Christophe  2
Affiliations

Optimization of energy recovery efficiency from sweet sorghum stems by ethanol and methane fermentation processes coupling

Bakari Hamadou et al. Bioengineered. 2023 Dec.

Abstract

Taken separately, a single sweet sorghum stem bioconversion process for bioethanol and biomethane production only leads to a partial conversion of organic matter. The direct fermentation of crushed whole stem coupled with the methanization of the subsequent solid residues in a two-stage process was experimented to improve energy bioconversion yield, efficiency, and profitability. The raw stalk calorific value was 17,144.17 kJ/kg DM. Fermentation step performed using Saccharomyces cerevisiae resulted in a bioconversion yield of 261.18 g Eth/kg DM, i.e. an energy recovery efficiency of 6921.27 kJ/kg DM. The methanogenic potentials were 279 and 256 LCH4/kg DM, respectively, for raw stem and fermentation residues, i.e. energy yields of 10,013.31 and 9187.84 kJ/kg DM, respectively. Coupling processes have significantly increased yield and made it possible to reach 13,309.57 kJ/kg DM, i.e. 77.63% of raw stem energy recovery yield, compared to 40.37% and 58.40%, respectively, for single fermentation and methanization processes.

Keywords: Sorghum; bioconversion; bioenergy; biomass; energy efficiency; ethanol; methane.

Plain language summary

Sweet sorghum stem is a viable feedstock source for efficient coproduction of ethanol and methaneSorghum stems calorific value determination revealed an energy potential of 17.15 MJ/kg DMEnergy recovery by single methanization yielded 18.03% more than ethanol fermentationCoupling processes has significantly increased energy recovery yield and profitability.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

None
Graphical abstract
Figure 1.
Figure 1.
Overall research implementation flow.
Figure 2.
Figure 2.
Structure of raw sorghum stalk fibers before fermentation (a) and mixture of sorghum stalk fibers and microbial biomass after fermentation (b).
Figure 3.
Figure 3.
Kinetics of different biomass fractions fermentation: (a) shredded whole stalk and marrow, (b) juice and glucose control.
Figure 4.
Figure 4.
Ethanol fermentation and bioconversion yields for different biomass fractions.
Figure 5.
Figure 5.
Energy efficiency of different biomass bioconversion processes.
Figure 6.
Figure 6.
Kinetics of cumulative methane production (a) and evolution of biomass methanogenic potential (b). Evolution of CH4 and CO2 contents as a function of hydraulic retention time for raw stem (c) and solid ethanol fermentation residues (d).
See this image and copyright information in PMC

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