[Digestion] Biogas plant at Zoo

[Anand Karve]

Dear Mr. Eaton,
one can very easily dry dung, at least in a semi-arid country like India,
by just exposing it to sunlight. For greater output, one can use a filter
press, as is used in a sugar factory to separate fine particles of bagasse
from sugarcane juice. Dung cakes is a source of income to villagers. 40 kg
dung, which is required daily as input in a family size biogas plant,
yields dung cakes that can be sold in India for about US$1. It requires
daily only about 2 to 3 kg of cotton stalks to cook the the daily meals for
a family of 5, if it uses an improved stove based on the rocket or TLUD
principle. Woody agricultural waste like stalks of cotton and pigeonpea, or
shanks of maize are readily available to rural people. They are not a
saleable commodity, and therefore they are available free of cost. *B*ecause
of the reason that dung cakes are a saleable commodity, people in
Indian rural areas have refused to use biogas plants based on dung. In
spite of all the propaganda by Government of India and a subsidy of 20% on
the cost of construction, less than 2% of the Indian rural population
has working dung based biogas plants.
         I agree with your view that a biogas plant in a zoo would
eliminate the waste and would also have educative value. But the education
should be all-inclusive and not one-sided. For instance, it should be
taught to the public that making biogas from dung is a wasteful process.
1kg dry dung would give about 3500 to 4000 kcal/kg if burned directly,
whereas the same quantity of dung would yield only 600 kcal/kg if it is
converted into biogas. They should also be told the truth about the
virtues of biogas slurry as fertilizer.  In organic agriculture, the plants
get the major part of their minerals from the soil itself, and not from the
decomposed organic matter. The organic matter is used up mainly by the soil
micro-organisms to multiply their numbers. It is an accepted fact that
the number of microbes in the soil is directly correlated to soil
fertility. Therefore the aim of organic farming should be to increase the
number of microbes in the soil, and therefore a farmer should apply high
calorie, non-composted organic material to the soil. If one were to provide
all the plant nutrients to one's crop through compost, one would require 50
ton compost per ha per crop. There are literally thousands of farmers
in Maharashtra State, India, who apply only about 25 kg sugar or 125 kg
green leaves per ha, once every three months, to their field, and get very
high yields.     Yours
A.D.Karve

On Fri, Jun 28, 2013 at 8:28 AM, Alexander Eaton
<alex at sistemabiobolsa.com>wrote:

> Dr. Karve,
>
> You have held this stance in many past posts, comparing starch to waste,
> and arguing waste as not an ideal feedstock for AD.  I have always thought
> that your point is valid, but a bit academic and missing the fact that AD
> systems can be seen as an extension of the animal digestive system,
> treating waste further and extracting energy that has not been used.
>  Clearly starch creates more gas, but the questions posed here is not about
> choosing starch or animal dung for a digester, it is about whether a zoo
> would be wise to consider a digester to treat animal waste and recover
> energy.  Is dedicating space and time at a zoo to dehydrating animal dung
> and then developing a system to burn it and recover the energy really a
> better alternative than an AD system?  From an energy and process balance,
> can you explain a system that would perform better than a digester in this
> context?
>
> Best,
>
> A
>
>
>
>
>
>
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