Table 6.
Gibbs free energy of the anaerobic oxidation of acetate, methane, and alkanes using sulfate as an electron acceptor (conditions shown are at standard temperature and pressure).
| Sulfate reduction process | Reaction | ΔG0 (kJ/mol SO2−4)* | Carbon source: SSO2−4 | C:SO2−4 | |
|---|---|---|---|---|---|
| 1 | Heterotrophic (acetate) | SO2−4 + CH3COO− → 2HCO−3 + HS− | −47.7 | 1:1 | 2:1 |
| 2 | Heterotrophic (methane) | SO2−4 + CH4 → HCO−3 + HS− + H2O | −33 | 1:1 | 1:1 |
| 3 | Heterotrophic (ethane) | 14SO2−4 + 8C2H6 → 14HS− + 16HCO−3 + 8H2O + 2H+ | −39.81 | 8:14 | 16:14 |
| 4 | Heterotrophic (propane) | 5SO2−4 + 2C3H8 → 6HCO−3 + 5HS− + H+ + 2H2O | −33.06 | 2:5 | 6:5 |
| 5 | Heterotrophic (butane) | 26SO2−4 + 9C4H10 + 4H2O → 36HCO−3 + 36H+ + 26HS− | −14 | 9:26 | 18:13 |
| 6 | Autotrophic (with H2) | SO2−4 + 2HCO−3 + 8H2 + 2H+ →CH3COO− + HS− + 8H2O | −336.5 | 2:1 | 2:1 |
Autotrophic sulfate reduction, in which hydrogen is used to reduce inorganic carbon, is shown for reference.
*
Δ G0 Values reported are those calculated under standard conditions of 1 M concentrations for soluble reactants, 1 atmosphere pressure for gases, 298.15 K temperature at pH 7.0 and are calculated using values from the CRC Handbook for Chemistry and Physics (http://www.hbcpnetbase.com/).