Modeling of Biogas Reactors

180 6 Modeling of Biogas Reactors
usual range of substrate concentrations. If the system was heavily overloaded for
some time and was out of the described range, the microbial population might need
some recovering time, which cannot be described by Eq. 18. Figure 6.16 shows a
sketch of different configurations in which active microorganisms exist in biogas reactors.
They can exist in a freely dispersed form, i.e., as single organisms, or as in the
biogas tower reactor in the form of loose pellets. The microbial system can also be
immobilized in the form of a film on the wall or as a dense pellet. In the second case
the conversion efficiency is also influenced by transport phenomena. The data given
in Eq. 18 hold only for freely dispersed organisms. When immobilized microorganisms
dominate in a biogas reactor the constants (both saturation and inhibition constants)
are larger.
Eq. 18 can also be used to calculate the combined influence of two parameters as
demonstrated in Figure 6.17. This graph shows the gas production as a function of
Fig. 6.16 Configuration of the active microbial system.
Fig. 6.17 Methane production as a function of the concentration of total acetic acid at different
concentrations of total hydrogen sulfide (c HPro = 0).