Table 1
Stoichiometric relationship for methanogenesis of anaerobic digestion process
Vapour/liquid transitions Electrolytes transitions Redox reaction
C2H4O2 (g)C2H4O2 C2H4O2C2H3O2
− +H+ C2H4O2 +2H2O2CO2 +8H+ +8e−
H2O (g)H2O H2OH+ +OH− CH4 +2H2OCO2 +8H+ +8e−
CH4 (g)CH4 CO2 +H2OH2CO3 H22H+ +2e−
H2 (g)H2 CO2 +H2OHCO3
− +H+ 2H2O (l)O2 (g) + 4H+ +4e−
CO2 (g)CO2 CO2 +H2OCO3
−2 +2H+
constant (K).
ln K =
−
i
viμ
◦
i
RT
=
i
ln avi
i (3)
Examples of equilibria and their thermodynamic laws based
on Eq. (3) are shown in Table 2. The equilibrium constant (K) in
Eq. (3) can also be applied to the anaerobic digestion process.We
categorised the equilibrium relationships in anaerobic digestion
into three types: vapour/liquid, electrolyte ionisation, and Redox
equilibrium.