Page 215 - Advances in Eco-Fuels for a Sustainable Environment

Anaerobic digestion of various feedstocks for second-generation biofuel production 179

production. But the advantages that can be understood from codigestion and the
expected drawbacks that we come across need to be assessed carefully. The inhibition
can be local in a solid heterogeneous complex and all the inhibitions are boosted by the
quantity of solid waste used [95]. There is a lack of inoculum acclimation study. The
inhibition process in a highly fermentable substrate leads to low production of meth-
ane. It also affects the size of the biogas plant and process drifts, which ultimately
results in low profitability.

6.11.6 Changing aspects of microbial population

The anaerobic digestion fundamentally depends upon the dynamics of the microbial
populations. The population growth of these microbial communities depends upon the
environment conditions. The activities of the microbial communities re also affected
by the surrounding environment conditions [96]. The total solid content in the anaer-
obic digestion also plays an important role in regard to microbial communities such as
in the case study of the analysis of household garbage waste containing 10%–35% of
total solid content, which showed an impact on the activity of microbial communities
[96]. The solid-state studies regarding population dynamics are very few; mostly, the
population dynamics in the liquid state are studied and documented [97]. The study
becomes even tougher because the development of the biofilm can interfere with the
biogas transfer and hydric transfer. This challenges the study of microbial population
dynamics even greater when there are no reliable monitoring indicators. The liquid
phase management depends on the process; a recent study [98] of anaerobic digestion
of cow manure in a reactor with a capacity of 8L was unable to deliver proof for trans-
fers of microbial populations between the liquid and the solid phases of the investi-
gation, or key fluctuations as a function of the depth of the sampling.

6.12 Conclusion

The biogas production from anaerobic digestion is affected by temperature, pressure,
pH inside the digester, carbon nitrogen ratio in the feedstock, and the type of digester
used. The composition of biogas mainly depends on the activity of the different types
of microorganisms that take part in the decomposition of the substrate at the various
levels. The activity of these microorganisms mainly depends on the temperature, pH,
and pressure; this also applies to their survival and reproduction. The favorable tem-
perature range seen was 50–60°C and the pH level inside the digester for producing
higher methane in the biogas and a higher activity of the microorganism ranges from
5.5 to 7.5, depending on the stages of the anaerobic digester. The carbon-nitrogen ratio
affects the pH value, and therefore the activity of the microorganism and biogas pro-
duction. The maximum carbon nitrogen ratio allowed for having a pH value close to 7
is 30:1. The HRT is 25 days longer in a two-stage mesophilic digester than a single-
stage thermophilic digester. It is so because the temperature in the thermophilic
digester is 20°C higher than the mesophilic digester, which helps the thermophilic
digester increase the activity of the microorganisms. To improve the anaerobic