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

Table 1 Main balance reactions presented in anaerobic microbial fermentation

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

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].

ISSN: 2731-3654