Bioengineering of anaerobic digestion for volatile fatty acids, hydrogen or methane production: A critical review

Figures & data

Table 1. Physicochemical properties and potential applications of individual volatile fatty acids.

VFA	Molecular formula	Molecular weight (g/mol)	Boiling point (°C)	pKa	Area of application
Acetic	CH3COOH	60.05	118	4.76	Food additives, plasticizers, dyes
Propionic	CH3CH2COOH	74.08	141	4.88	Resins, pharmaceuticals, paints
Isobutyric	(CH3)2CHCOOH	88.11	154	4.84	Pesticides, food additives, paints
Butyric	CH3CH2CH2COOH	88.11	164	4.82	Perfumes, textiles, vanishes, plastics
Isovaleric	(CH3)2CHCH2COOH	102.13	177	4.77	Pharmaceuticals, perfumes, fungicides
Valeric	CH3(CH2)3COOH	102.13	185	4.84	Perfumes, plasticizers, lubricants
Caproic	CH3(CH2)4COOH	116.16	205	4.88	Rubber, grease, tobacco flavor

Table 2. First-order hydrolysis constants for selected macromolecules in organic wastes [81].

Substrate	T (°C)	First-order rate constant (day ^−1)	Mode of cultivation
Starch	35	0.20–1.08	Semi-continuous
Cellulose	35	0.12	Batch
Cellulose	35	0.28–0.52	Semi-continuous
Glutamic acid	35	1.12	Semi-continuous
Leucine	35	0.31–0.63	Semi-continuous
Gelatin	37	0.60	Batch

Figure 1. Schematic flow of the reactions involved in formation of volatile fatty acids coupled with the product extraction during anaerobic digestion.

Table 3. Typical kinetic constants during acidogenesis of hydrolysis products [74,81].

Substrate	µmax (day^−1)	YX/S (mg VSS/mg COD)	KS (mg COD/L)	Doubling time (h)	b (day^−1)
Glucose	1.25	0.162	22.5^a	0.5	–
Glucose	0.3	0.15	400^a	2.3	–
Cellulose	0.071	0.16	36.8^a	9.8	–
Unsaturated oleic acid	0.44	0.11	3180	–	0.01
Unsaturated linoleic acid	0.55	0.11	1816	–	0.01
Saturated myristic acid	0.105	0.11	105	–	0.01
Saturated stearic acid	0.085	0.11	417	–	0.01

 

^{a= reported as mg/L}

Pavlostathis SG, Giraldo‐Gomez E. Kinetics of anaerobic treatment: A critical review. Crit Rev Environ Control. 1991;21(5–6):411–490.

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Gavala HN, Angelidaki I, Ahring BK, et al. Kinetics and modeling of anaerobic digestion process. In: Ahring BK et al., editors. Biomethanation I. Berlin, Heidelberg: Springer; 2003. p. 57–93.

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