Glycerol fermentation by (open) mixed cultures: a chemostat study

Area of Science:

• Biotechnology and Bioengineering
• Microbial Fermentation
• Sustainable Chemistry

Background:

• Glycerol is a significant byproduct of bioethanol and biodiesel production.
• Valorization of glycerol into valuable chemicals is crucial for biorefinery sustainability.
• Mixed culture fermentation offers a robust approach for chemical production from diverse substrates.

Purpose of the Study:

• To evaluate the potential of glycerol as a substrate for mixed culture fermentation.
• To determine the product spectrum of glycerol fermentation compared to glucose.
• To investigate the co-fermentation of glucose and glycerol.

Main Methods:

• Operation of two parallel chemostat reactors at pH 8 and a dilution rate of 0.1 h(-1).
• Fermentation of glycerol and glucose as sole carbon sources.
• Co-fermentation experiments with mixed glucose-glycerol cultures.

Main Results:

• Glycerol fermentation predominantly produced ethanol and formate (1:1 ratio) under substrate-limiting conditions.
• Product spectrum shifted to 1,3-propanediol and acetate (2:1 ratio) at increased glycerol concentrations.
• Co-fermentation of glucose and glycerol yielded ethanol and butyrate as major products (38% and 34% COD converted, respectively).

Conclusions:

• Glycerol can be effectively converted into bulk chemicals like ethanol and formate via mixed culture fermentation.
• Product distribution is sensitive to substrate concentration and microbial community composition.
• Metabolic pathways and constraints, including ATP production and redox balancing, explain observed fermentation products.