Submitted to: Fermentation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2019
Publication Date: 10/24/2019
Publication URL: https://handle.nal.usda.gov/10113/6811096
Citation: Nghiem, N.P., Toht, M.J. 2019. Pretreatment of sweet sorghum bagasse for ethanol production using Na2CO3 obtained by NaOH absorption of CO2 generated in sweet sorghum juice ethanol fermentation. Fermentation. 5(4)91:1-10. https://doi.org/10.3390/fermentation5040091.
Interpretive Summary: Commercial production of fuel ethanol currently use sugarcane and corn as feedstocks. Attempts to develop other renewable feedstocks that are more abundant have led to lignocellulosic biomass (in short, biomass). Biomass requires “pretreatment” to open up the structure to improve degradation by enzymes for production of fermentable sugars, which subsequently are fermented to ethanol. In ethanol fermentation, the major co-product is carbon dioxide (CO2), which is a green-house gas and contributes to global warming. One of the largest cost components of biomass pretreatment is chemical cost. In the present study, the CO2 produced in sweet sorghum juice (SSJ) ethanol fermentation was captured by absorption in a base (sodium hydroxide - NaOH) solution. The product of absorption was a solution of sodium carbonate (Na2CO3). This Na2CO3 solution was used for pretreatment of sweet sorghum bagasse (SSB), which is the solid residue in SSJ extraction from the stalks. The pretreated SSB was fermented together with SSJ to produce additional ethanol. The results showed: 1. CO2 absorption efficiency of 92.0%; 2. Very little loss of the carbohydrate fractions in the SSB; 3.Additional ethanol could be produced from the pretreated SSB by yeast at 81.7% of the theoretical value.
Technical Abstract: (1) Background: Commercial production of fuel ethanol currently use sugarcane and corn as feedstocks. Attempts to develop other renewable feedstocks that are more abundant have led to lignocellulosic biomass, which requires pretreatment prior to enzymatic hydrolysis to generate fermentable sugars. One of the largest cost components of pretreatment is chemical cost. Ethanol fermentation also produces large quantities of CO2 as a co-product contributing to the global warming. (2) Methods: Sweet sorghum has emerged as a potential new feedstock for ethanol production. In the present study, the CO2 produced in sweet sorghum juice (SSJ) fermentation was captured by absorption in 5 M NaOH. The resultant Na2CO3 solution was used for pretreatment of sweet sorghum bagasse (SSB), which is the solid residue in SSJ extraction. The pretreated SSB was fermented in SSJ to produce additional ethanol. (3) Results: CO2 absorption efficiency of 92.0% was observed. Pretreatment of SSB by the obtained Na2CO3 solution resulted in no loss of glucan and only 8.1 wt% loss of xylan. Ethanol yield from glucan in the pretreated SSB was 81.7% theoretical. (4) Conclusions: CO2 from SSJ fermentation captured as Na2CO3 could be used for efficient SSB pretreatment. Further study focusing on pretreatment process optimization is needed.