Environmental Engineering Reference
In-Depth Information
3.11 Influence of oxidation state on gas composition (adapted from
Speece, 1996).
to a very limited extent. Furthermore, a BMP test is quite complex and
errors can occur quite easily, as explained in Section 3.3.7.
Continuous tests
The most accurate data on biogas production from a feedstock or feedstock
mixture can be obtained from continuous fermentation tests (see Section
3.4.5). However, these tests are rarely done for the sole purpose of
estimating the energy recovery potential due to the very great effort and
costs involved.
3.5.2 Influence of carbon oxidation state on methane
concentration
The methane concentration in biogas can be estimated using the Buswell
formula or according to feed analysis. The relationship between carbon
dioxide and methane in biogas depends on the mean oxidation state of
carbon in the feedstock. Figure 3.11 gives a good overview of the mean
oxidation state of different substrates and the corresponding CO
2
and CH
4
concentrations.
Carbohydrates show CH
4
concentrations of about 50%, proteins in the
range of 55-70% and fats between 70 and 75%. The feed that actually goes
into biogas plants is more likely to be a mixture of these components.
Therefore, in most biogas plants, the CH
4
concentration of biogas lies
between 50 and 60%. In addition, it should be mentioned that some of the
Search WWH ::
Custom Search