BIOCHEMICAL CONVERSION: ANAEROBIC DIGESTION - Biomass as a Sustainable Energy Source for the Future - page 450

Biomass measurement:

COD = 150 g O 2 . kg -1
ODM = 118g ODM . kg -1
N org =3g N . kg -1

Elemental composition:
CH 2.37 O 0.84 N 0.05

Stoichiometric coeficients:
CH 4 = 0.57
CO 2 = 0.38
NH 4 HCO 3 = 0.05
H 2 O = -0.08

Building block
composition:
PR = 0.20
LIP = 0.32
CHO = 0.48

Biogas composition:
CH 4 60 vol.%, CO 2 40 vol.%
Biogas production:
Biogas = 94 L . kg -1

biomass

FIGURE 14.4 Calculation example demonstrating the characterization of a wet organic substrate
in terms of its elemental composition, building block composition, and end product formation
stoichiometry, enabling the estimation of biogas production and composition. Full biodegradation
is assumed, but a correction for the actual biodegradable fraction can readily be implemented.

(van Lier et al., 2008). In the section on biogas upgrading and utilization , it is shown
that hydrogen sulfide removal from biogas is required to avoid sulfuric acid produc-
tion and corrosion in a biogas burner.

14.2.3.2 Temperature Three major temperature operating ranges can be distin-
guished in anaerobic digestion. These are psychrophilic (4 15 C), mesophilic −

65 C) temperatures. While reactors can operate
between these ranges effectively, optimal temperatures for mesophilic and thermo-
philic organisms are approximately 35 and 55 C, respectively.
The influence of the temperature on biochemical systems can be summarized as
follows:

40 C), and thermophilic (45

(20 − −

￿ Increase in reaction rates with increasing temperature as predicted by the Arrhe-

nius equation

￿ Rapid decrease in reaction rate with increasing temperature above the optimum

temperature (>40 C for mesophilic and >65 C for thermophilic systems)

￿ Increase in biochemical energy requirements for maintenance purposes with

increasing temperature, resulting in lower biomass yield on substrate