Modeling of Biogas Reactors

170 6 Modeling of Biogas Reactors
Fig. 6.6 Calibration of the silicon membrane probe coupled to mass spectrometer measuring
the dissolved CO 2 in desalinated water (after Polomski, 1998).
means of isocratic cation exchange chromatography. For the detection of betaine
and N,N-DMG an ultraviolet detector was used. All other substances were detected
by conductivity.
Besides other organic components, such as acetic and propionic acid, betaine is
the dominant organic substance in the wastewater. Up to 33% of the TOC is represented
by betaine. The use of HPLC analysis combined with an automated ultrafiltration
setup for online process monitoring gives interesting information about the
dynamic behavior of the anaerobic process, as demonstrated in Figure 6.7. The
graphs show the effect of hydrogen sulfide elimination from the fermentation broth.
The concentration of undissociated H 2S was decreased by a factor of 2 (from 300 to
150 mg L –1 ). During the same time biogas production increased. The concentration
of acetic acid decreased while the other acids measured remained more or less
stable. Betaine was completely degraded only at lower H 2S concentrations. Interestingly,
the concentration of N,N-DMG, which is a metabolic product of the anaerobic
degradation of betaine, is also decreased.
6.3
Kinetics
The anaerobic degradation of organic substances is performed in a sequence of
biological reactions in a synthrophic cooperation of different microorganisms