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Table 1 Main balance reactions presented in anaerobic microbial fermentation

From: Total solids content: a key parameter of metabolic pathways in dry anaerobic digestion

Metabolic pathway Equation number Type of fermentation Reaction Informative products
Hydrogen-producing 1 Glucose fermentation C6H12O6 + 2H2O → 2CH3COOH + 2CO2 + 4H2 Acetic acid, hydrogen
Hydrogen-producing 2 Glucose fermentation C6H12O6 → CH3CH2CH2COOH + 2CO2 + 2H2 Butyric acid, hydrogen
Hydrogen-producing 3 Propionic acid fermentation CH3CH2COOH + H2O → CH3COOH + CO2 + H2O + H2 Acetic acid, hydrogen
Hydrogen-consuming 4 Homoacetogenesis 2CO2 + 4H2 → CH3COOH + 2H2O Acetic acid
Hydrogen-consuming 5 Propionic acid production C6H12O6 + H2 → 2CH3CH2COOH + 2H2O Propionic acid
Other metabolism 6 Propionic acid and ethanol consumption CH3CH2OH + CH3CH2COOH → CH3CH2CH2CH2COOH + H2O Valeric acid
Other metabolism 7 Butyric acid and ethanol consumption CH3CH2OH + CH3CH2CH2COOH → CH3CH2CH2CH2CH2COOH + H2O Caproic acid
Other metabolism 8 Glucose fermentation C6H12O6 → 2CH3CH2OH + 2CO2 Ethanol
Other metabolism 9 Glucose fermentation C6H12O6 → 2CH3CHOHCOOH + 2CO2 Lactic acid
  1. Hydrogen-producing, hydrogen-consuming, and other metabolites are produced during acidogenesis and reveal the use of the substrate. For a more efficient methanogenesis, hydrogen-producing pathways should be favored. Adapted from Guo et al. [16], Valdez-Vazquez and Poggi-Varaldo [17], Cord-Ruwisch et al. [22], and Stadtman et al. [23].