1. Bioenergy-Fermentation
Wood Chemistry PSE 406
Bioenergy-Fermentation

2. Agenda What is fermentation? Fermentation inhibitors
Separate Hydrolysis and Fermentation (SHF) and Simultaneous Saccharification and Fermentation (SSF)

3. Bioconversion of biomass to ethanol (pretreatment)
Liquid
phase
Sugars
Ethanol
Pretreatment
Fermentation
Biomass
Lignin
Recovery
Solid phase
Cellulose
Hydrolysis
Fermentation
Sugars
Ethanol

4. Fermentation Defined as:
Cellular metabolism under anaerobic conditions (absence of oxygen) for the production of energy and metabolic intermediates
Many organisms can “ferment” (i.e., grow anaerobically)
Not all produce ethanol as an end-product of fermentation
Butanol
Acetic acid
Propionic acid
Lactic acid

5. Strain selection
Choice of microorganism for ethanol production has traditionally been a Yeast
Yeast:
Single cell microorganism
Fungi
Facultative anaerobe
Most common industrial fermenter is Saccharomyces cerevisiae (baker’s or brewer’s yeast)
Why?

6. Why S. cerevisiae? Has been selected over thousands of years
High ethanol yield and productivity
Relatively simple to culture
G.R.A.S organism
Robust:
High ethanol tolerance
Resistant to inhibitors

7. Fermentation (1)

8. Fermentation (2) Conversion factor 0.51
1g/L of glucose: 0.51g/L ethanol (maximum)

9. Inhibitors 5 groups of inhibitors
Released during pretreatment and hydrolysis
Acetic acid and extractives
By-products of pretreatment and hydrolysis
HMFs and furfurals, formic acid
Lignin degradation products
Aromatic compounds
Fermentation products
Ethanol, acetic acid, glycerol, lactic acid
Metals released from equipment

10. HMFs and Furfurals
Reactions occuring during hydrolysis of lignocellulosic materials. The furan derivatives and phenolic compounds will react further to form some polymeric material

11. HMFs, Furfurals
Figure 29 Utilisation of 5-HMF and furfurals during SSF at various solid consistencies by Saccharomyces cerevisiae. Error bars represent the range of duplicate experiments.

12. Experimental Corn fibre Hydrolysis SHF Corn fibre SSF Steam Explosion
(solid +liquid
fraction)
Corn
fibre
Hydrolysis
Fermentation
SHF
50°C, pH 4.8
48 hours
30°C, pH 6
12 hours
Steam
Explosion
(solid +liquid
fraction)
Corn
fibre
SSF
37°C, pH 5
24 hours

13. Pros and cons of SHF and SSF
Separate temp. for each step (hydrolysis 50°C, fermentation 30°C)
Possibility of yeast and enzyme recovery
Cons
Requires two sets of fermenters
End-product inhibition
Pros
Minimized end-product inhibition
Requires only one set of fermenters
Cons
Difficulties in recovery and yeast and enzyme recycling
Temperature/pH compromise (37°C)

14. SHF versus SSF SSF (91%-6C)-24 hours Corn fibre SHF (75%-6C)-60 hours
Steam
Explosion
(solid +liquid
fraction)
SSF (91%-6C)-24 hours
Corn
fibre
95%
SHF (75%-6C)-60 hours

15. SSF versus SHF
Hexose consumption and ethanol production during SSF and SHF at 37°C with 10, 20 and 40 FPU g cellulose-1 of the combined water soluble and insoluble fractions at 8% (w/v) consistency solids at an IU:FPU ratio of 2:1. Error bars represent the range of duplicate experiments. The numbers in the legend show the relative ethanol yield (%) and ethanol productivity (g L-1 h-1). The ethanol productivity was calculated as ethanol produced (g L-1) within first 12 hours for SSF and hours for SHF