Table 3.

Possible reactions involved in glycerol degradation by the enrichment cultures Gly(9) and Col‐Gly and their corresponding Gibbs free energy changes at 25°C.

Reaction	Reactant	Main products	Equation	ΔG 0’ (kJ reaction−1)a
(1)	Glycerol	Acetate	C3H8O3 + 2 H2O → C2H3O2 ‐ + HCO3 ‐ + 3 H2 + 2 H+	−73.1
(2)	H2 + CO2	Methane	4 H2 + ${\text{HCO}}_3^{-}$ + H+ → CH4 + 3 H2O	−135.6
(3) = (1 + 2)	Glycerol	Acetate + Methane	C3H8O3 → ${\mathrm{C}}_2{\mathrm{H}}_3{\mathrm{O}}_2^{-}$ + 0.75 CH4 + 0.25 ${\text{HCO}}_3^{-}$ + 0.25 H2O + 1.25 H+	−174.7
(4)	Glycerol	Lactate	C3H8O3 → ${\mathrm{C}}_3{\mathrm{H}}_5{\mathrm{O}}_3^{-}$ + H2 + H+	−69.1
(5)	Glycerol	Ethanol	C3H8O3 + H2O → C2H4OH + ${\text{HCO}}_3^{-}$ + H2 + H+	−82.7

^aGibbs free energy changes (at 25°C) calculated under standard conditions (solute concentrations of 1 mM and gas partial pressure of 10⁵ Pa) at pH 7. Standard free energies of formation were obtained from Thauer et al. (1977) (Thauer et al., 1977).