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Anaerobic digestion of various feedstocks for second-generation biofuel production 177

interlaboratory assay [83] comprising certain laboratories has revealed that the coef-
ficient of variation of interlaboratory repeatability varies approximately 10% while
interlaboratory reproducibility had a coefficient of variation of approximately 20%
for a given sample, even though protocols used were different subjected to the labo-
ratory. By preserving a sample and identical protocols, interlaboratory reproducibility
indicated a coefficient of variation of 17%, while the coefficient of variation of 5%
was observed for the repeatability of the interlaboratory. The methodology used to
determine the gas [84] overestimated the results by 15% for monomeric methods rel-
ative to volumetric methods. The other difficulty related to BMP is inoculum, which
will be explained in detail later. There cannot be a single and standardized substrate
for representing the warm control sample, which can include all the inoculum used.

6.11.3 Inoculum
The inoculum in the liquid state is a significant factor in anaerobic digestion in solid
phase because it is very useful to convey the micro-organisms, the water of rec-
irculation [85]. The anaerobic digestion of maize showed the importance of the inoc-
ulum used for the degradation of waste [86]. The second important parameter that
affects the inoculum is the amount of waste degraded. If this size is very large, it
may quickly result in inhibition [87]. Still, there isn’t much knowledge about the activ-
ity of the inoculum. Many of the researchers struggle to study the aging of the inoc-
ulum due to its poor documentation. Other observations regarding this issue are lack of
recommendations to accumulate, storage of the inoculum, and lack of a microbial
dynamics study. These issues lead to process drifts, lack of profitability, and decreases
in methane production.

6.11.4 Hydrodynamic, hydric transfers, and rheology
The properties associated with a medium such as the micro and the macroporosity, the
permeability, the degree of compaction, etc.—belonging to hydrodynamics have
undergone few studies to date, and they represent the fundamentals of the process.
The following observations such as lack of knowledge, hydrodynamic parameters
of the medium are less studied, and diffusion and convection are less analyzed. Along
with this, liquid repartition in solid media is less investigated, and biodegradation and
setting of solid media during anaerobic digestion are less studied. There is a lack of
liquid-phase management by recirculation and immersion. The study of hydrodynam-
ics of anaerobic digestion becomes critical due to the dependence on nature and the
content of the substrate, which becomes an important parameter for the hydrodynam-
ics of anaerobic digestion. The dynamic study of percolation of a liquid state over a
solid entity is more complex than it looks, but it is an established process. A case study
of this issue, [88] a method based on columns of hundred liters of cow manure, has
been formulated to identify the hydrodynamic properties of the medium. The produc-
tion of methane is affected by the size of the particles because the size of the particles
differs each time the activity on the particle becomes different and thus does not lead
to the same range of production of methane [88].