Microorganisms as agents of change (for the better)
o Production of biofuels
o Chemical intermediates
o Transportation fuel made from renewable feedstocks
o Oxygenate to improve combustion and reduce emissions
Contains more oxygen so burns cleaner, also at a lower temp. Reduces carbon
monoxide and greenhouse gas emission.
o Gasoline extender (energy independence, no longer need oil, etc.)
o Used in 5-10% blends, as a flex fuel (E85)
85% ethanol, 15% gasoline
o World ethanol production has been increasing rapidly since the 1970’s, especially to be
used as fuel (as beverage has remained about the same, slight increase in industrial)
Largest increase in the United States (want fuel independence)
o Sugarn can has the best energy balance, wheat and corn the worst.
Amount of energy input into the process compared to the energy released by
burning the resulting product.
o Ethanol is a clean burning fuel (leaves little contamination) Fermentation Conditions
Temperature below 34 centigrade
Micro-aerobic conditions (concentration oxygen less than air)
Minimal additional nutrients required
Extensive heat evolution
Ethanol yield approx. 0.5kg EtOH/kg fermentable sugars
Features of Ethanol Fermentation
End product inhibition (EPI): kinetic (doesn’t reach thermodynamic eqm) and process limitation
Fermentation vs. Recovery trade-off: recovery wins
Low productivity (efficiency)
A lot of water
Microbiology – Engineer a better organism via genetic/metabolic engineering
o Ethanol tolerant yeast
o High temperature yeast
o C5 sugar fermenters
o Fermenting organisms that produce hydrolytic enzymes, etc.
Biochemical engineering – design a better process
Ethanol as a Microbial Biotechnology Process
Long standing, well-established process with societal and industrial acceptance
Provides public acceptance of other biofuels in future (e.g. biodiesel)
Multiple renewable biomass feedstocks
Still questions regarding food/fuel and energy balance
Cellulosic ethanol in near future (biofuel from wood, grasses, inedible plant parts)
Typical example of end product inhibition bioprocess
Biobutanol and Aceton-Butanol-Ethanol (ABE) Fermentation
Butanol can be blended with traditional unleaded gasoline just like ethanol, but at larger
concentrations than ethanol-gasoline blends.
Energy content of butanol is higher than ethanol and about the same as gasoline – will yield fuel
consumption close to that of gasoline.
Evaporates more slowly than ethanol and vapours do not case smog.
Can be transported through existing pipelines for distribution since it’s less hygroscopic (absorbs
water) than ethanol and is less susceptible to separation in presence of water.
When petrochemical production of solvents became easier and cheaper in the 1960s,
fermentation processes began to experience a decline. Process features:
Anaerobic, usually use Clostridium acetobutylicum
Acid production (acidogenic) followed by solvent production (solventogenic)
A:B:E = 3:6:1
Slow (2 – 6 days)
The final total concentration of ABE solvents produced ranges from 12 – 20 g/L
End product inhibition!
ABE Fermentation: Current trends
High feedstock cost significantly increase operating Transition towards cheaper (and more sustainable)
costs feedstocks e.g. wastes and agricultural residues.
Low butanol titres increase recovery costs, reduce Develop improved microbes with improved
sugar loadings and increase water usage. solvent titres or develop methods for in situ
product removal to alleviate end product
Low butanol yield increases feedstock costs. Develop improved microbes with higher butanol
yields or higher butanol:solvent ratios.
Low volumetric solvent productivities increase Develop continuous fermentation processes that
capital and operating costs. reduce time and increase volumetric productivity
Solvent recovery using conventional distillation is Develop low energy methods for solvent recovery
energy intensive and relatively expensive. and purification. Recovery also improved by
improving solvent titre.
High water usage is not sustainable and increases Recycle process water back through the
the cost of effluent treatment. fermentation.
The Development of Antibiotics: A Paradigm fo