Page 214 - Advances in Eco-Fuels for a Sustainable Environment

178 Advances in Eco-Fuels for a Sustainable Environment

It does not have optimization nor of comprehension of the bad distribution of the
liquid in the solid phase in the process, returns the phase solid partially degraded and
the impact on the production of methane and profitability. The rheological and hydro-
dynamic behavior is influenced by many other factors in the solid-state matter in the
process of anaerobic digestion. One such factor is biofilm development in the solid
matter [89]. Due to the development of the biofilm, the permeability of the medium
gets negatively affected and hence changes the porosity of the medium. This blocking
of pores will restrict the transfer of biogas as well as hydric transfer [90].
With water being the main component of the solid matter anaerobic digestion, a
linear relation of it with methanogenic activity was found [91]. But the location of
water in the solid entity is still hard. There are various methods to measure the local-
ized water content in the medium, but they alter the experiment in many ways and
result in biasing the true results of the experiment. Methods such as using neutron,
TDR, or capacitive probes, fiberoptics, etc., would require a substantial number of
cables, probes, or fiberoptic cables to properly measure the localized content. The
application of such a method in the solid medium of such dimensions would be tough
and it would not signify the actual medium without probes. These probes and cables
would ultimately disturb the natural path of the liquid flow and will increase the num-
ber of flow paths, making the experiment less true and biased. There are successful
methods to determine the localized liquid in a solid entity. Cow manure is the most
general feed for anaerobic digestion and many researchers have found interesting
results and correlations, one of which is determining the partitioning and localized
liquid in the cow manure entity by the resistivity method after performing many mea-
surement sessions. In this method, the mapping of the reactor is possible, as is the
optimization. Electrical tomography methodology is also one such successful method
to locate the repartitioning of the liquid state as well as the fermented and
nonfermented areas.
Rheology is the study of the flow of liquid mediums or the deformation of solids
under conditions in which they respond with plastic flow. In the solid-state anaerobic
digestion, the study of rheology becomes quite exhaustive and complex because the
main component in this solid entity is the solid phase. This becomes the reason why
there are only a few studies describing the rheology solid medium [92]. There are only
a few studies about rheological properties and they show that they mainly depend on
the composition of waste. These properties get changed during the course of anaerobic
digestion [93]. It has been found that the rheological characteristic of the digestrate
behavior is viscoelastic. The flow depends mainly on the water content on the
biowaste, present in various forms, such as free water or water capillary or of the sur-
face, easy to drain, nonrelated to solid particles, present in spaces between microor-
ganisms and particles [94].

6.11.5 Codigestion and inhibition
Codigestion is the digestion in which a combination of selected biodegradable feed-
stocks has a base substrate mixed with a substrate that produces a large amount of
biogas per unit mass than the base substrate in order to maximize the biogas