Animal digestive strategies versus anaerobic digestion bioprocesses for biogas production from lignocellulosic biomass |
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Authors: | Ali Bayané and Serge R Guiot |
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Institution: | (1) Biotechnology Research Institute, National Research Council Canada, 6100 Royalmount Avenue, Montreal, QC, H4P 2R2, Canada; |
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Abstract: | Herbivorous mammals and wood-eating insects are fairly effective in the digestion of plant polymers, such as lignocellulosics.
In order to improve methane production from the lignocellulosic biomass, several kinds of anaerobic digestion processes derived
from animal models have been devised. However, the rates of biodegradation occurring in the anaerobic bioreactors still remain
lower than in animal guts. The effectiveness of the digestive systems of those animals results from the concerted action of
the various enzymes (e.g. cellulases, xylanases, esterases, ligninases) produced in their guts as well as their integration
with mechanical and chemical actions. Powerful pretreatment (prefermentation) operations are integrated to and support efficiently
the microbial fermentation system, e.g. the rumination (i.e. mechanical) in ruminants and the secretion of endogenous cellulases
(i.e. enzymatic) or the alkaline treatment (chemical) at mid-way in xylophagous insects. The oxygen gradients along the gastrointestinal
tract may also stimulate the hydrolytic activities of some microbial populations. In addition, the solid retention time, the
digesta flow and the removal of the end-products are well ordered to enable animals to thrive on a complex polymer such as
lignocellulose. At the same time, technologies were developed to degrade lignocellulosic biomass, such as the rumen derived
anaerobic digestion (RUDAD) process and the rumen simulating technique (RUSITEC), more elaborated and using rumen microbial
consortia. Overall, they showed that the fermentation taking place in the rumen fermentation and even in the hindgut are biological
processes that go beyond the limited environmental conditions generally found in anaerobic digesters. Hence, knowledge on
herbivores' digestion mechanisms might be better exploited in the design and operation of anaerobic digesters. This literature
review is a cross-analysis of the relevant information about the digestive strategies of herbivorous and wood-eating animals
and the bioengineering techniques in lignocelluloses degradation. The aim is to highlight strategies of animals' digestion
simulation for more effective anaerobic digestion of lignocellulosic compounds and other solid residues. |
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