[Digestion] Digestion Digest, Vol 53, Issue 8

[Hoysall Chanakya]

In response to Dr AD Karve,
"Dear Prof. Chanakya,
it is our experience that anything that is eaten by humans, cattle or
even by carnivores yields biogas if it is used as feedstock. This
automatically means that dry stalks of grass and cereal crops can be
used as feedstock in a biogas plant."

Ruminants take dry feed stocks a part of their diet and generally not as
the sole component.  It becomes the sole component in India and other
places when there is no fresh material.  This is because digestibility of
dried material is lower (both the extent of digestion and rate of
digestion).

This has something to do with plant physiology also - almost all living
plants pull out nutrients and usable carbon from its structural and leafy
parts at the end of its useful life.  Thus the naturally dried
(senescence) part or the dried straw of cereals are less digestible than
the fresh ones that are dried in an oven.

Second, dried feedstocks need to be hydrated for enzymes to function -
even if the material is powdered.  There is thus a discrepancy between
leaf litter and plucked leaves, dried straw and straw left in the field
after harvest, both in situ digestibility in the rumen or in the biogas
plant.

Finally, yes what ever animals and humans eat are certainly digestible
(with a few exceptions like betel nut, roasted coffee, etc).  The question
we need to address however is, can we get sensible rate of  biogas
production?

Best wishes
Chanakya


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