Table 2.
Gibbs free energy values for different methanogenesis substrates
| Substrate | Reaction equation | ΔG′° (kJ/mol CH4) |
|---|---|---|
| H2 + CO2 | 4 H2 + CO2 → CH4 + 2 H2O | − 131 (a) |
| HCOO− | 4 HCOO− + 4 H+ → CH4 + 3 CO2 + 2 H2O | − 145 (a) |
| CH3CH2OH + CO2 | 2 CH3CH2OH + CO2 → 2 CH3COOH + CH4 | − 121 (e) |
| H2 + CH3OH | CH3OH + H2 → CH4 + H2O | − 113 (e) |
| CH3OH + CH3CH2OH | 2 CH3OH + CH3CH2OH → 2 CH4 + H2O + CH3COOH | − 100 (b) |
| CH3CHOHCH3+ CO2 | 4 CH3CHOHCH3 + HCO3 + H+ → 4 CH3COCH3 + CH4 + 3 H2O | − 37 (c) |
| CH3OH | 4 CH3OH → CO2 + 3 CH4 + 2 H2O | − 107 (a) |
| CH3-COOH | CH3COOH → CO2 + CH4 | − 36 (a) |
| CH3-SH (CH3‑S‑R) | 4 CH3SH + 3 H2O → 3 CH4 + HCO3− + 4 HS− + 5 H+ | − 49 (b) |
| Betaine (CH3‑N‑R) | 4 (CH3)3N+CH2COO− + 2 H2O → 4 (CH3)2N+CH2COO− + 3 CH4 + CO2 | − 241 (c) |
| Choline (CH3‑N‑R) | 4 (CH3)3N+CH2CH2OH + 6 H2O → 4 H2NCH2CH2OH + 9 CH4 + 3 CO2 + 4 H+ | − 63 (d) |
| Trimethylamine (CH3‑N‑R) | 4 (CH3)3N + 6 H2O + 4 H+ → 4 NH4+ + 9 CH4 + 3 CO2 | − 31 (d) |
| 2-methoxyphenol (CH3‑O‑R) | 4 2-methoxyphenol + 2 H2O → 4 2-hydroxyphenol + CO2 + 3 CH4 | − 90 (f) |
The values for the standard free energy change (ΔG′°) are derived from (a) (Thauer 1998), (b) (Finster et al. 1992), (c) (Watkins et al. 2014), (d) (Watkins et al. 2012). (e) are values calculated by the webtool eQuilibrator (Flamholz et al. 2012) and (f) gives values calculated by use of the standard free energies of formation at 25 °C