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Published on: October 24, 2016
Ethanol production from corn starch in a fluidized-bed bioreactor
M S Krishnan1, N P Nghiem, B H Davison
1Bioprocessing Research and Development Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6226, USA.
Applied Biochemistry and Biotechnology
|August 12, 2004
Summary
This study optimized ethanol production from corn starch using immobilized enzymes and Zymomonas mobilis in a bioreactor. Separate hydrolysis and fermentation achieved higher ethanol yields and productivity compared to simultaneous processes.
Area of Science:
- Biotechnology
- Biochemical Engineering
- Industrial Microbiology
Background:
- Industrial dry-milled corn starch is a viable feedstock for bioethanol production.
- Immobilized biocatalysts offer advantages in bioreactor stability and reusability.
- Fluidized-bed bioreactors provide efficient mass transfer for enzymatic and microbial processes.
Purpose of the Study:
- To investigate and compare the efficiency of simultaneous saccharification and fermentation (SSF) versus separate hydrolysis and fermentation (SHF) for ethanol production from corn starch.
- To optimize ethanol yield and productivity using immobilized biocatalysts in a laboratory-scale fluidized-bed bioreactor.
- To identify the rate-limiting step in the SSF process.
Main Methods:
- Utilized a laboratory-scale fluidized-bed bioreactor with immobilized glucoamylase and Zymomonas mobilis.
- Performed simultaneous saccharification and fermentation (SSF) using co-immobilized biocatalysts in kappa-carrageenan beads.
- Conducted separate hydrolysis and fermentation (SHF) by first passing dextrin through an immobilized glucoamylase column, followed by fermentation with immobilized Z. mobilis.
Main Results:
- In SSF, dextrin conversion ranged from 54-89%, yielding 23-36 g/L ethanol at 9-15 g/L-h productivity, with saccharification identified as rate-limiting.
- In SHF, hydrolysis achieved >95% conversion yielding 162-172 g glucose/L.
- SHF resulted in higher ethanol concentrations (up to 70 g/L) and overall process productivity (up to 25 g/L-h) compared to SSF.
Conclusions:
- Separate hydrolysis and fermentation (SHF) is a more efficient strategy than simultaneous saccharification and fermentation (SSF) for producing ethanol from corn starch using immobilized biocatalysts.
- Optimized SHF process parameters led to significantly higher ethanol concentrations and productivities.
- The study demonstrates the potential of immobilized biocatalysis in fluidized-bed bioreactors for enhanced bioethanol production.
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