[Digestion] mixed waste AD

[Anand Karve]

Dear Deepak,
If I have understood you correctly, what you are planning to do is to have
a biphasic digestion system, in which the first tank would be for stirring
the material with water in an open tank, exposed to air, and to allow the
overflow from this tank to enter into the anaerobic digester. The quantity
of biogas generated by anaerobic digestion is directly proportional to the
digestibility of the feedstock. Human food consisting of sugar, starch,
protein and fats has high digestibility, so that 1 kg (dry weight) of any
of the above substances would yield about 1 kg biogas, if it is introduced
directly into an anaerobic digester. In the case of green leaves, the
midribs and veins, consisting of lignin, cannot be digested by the
methanogens, so that the digestible matter constitutes only about half the
dry weight. You would therefore have to introduce about 2 kg (dry weight)
of leaves into the anaerobic digester to produce 1 kg biogas.  In
comparison to the anaerobic microbes, the aerobic micro-organisms are much
more efficient in breaking down biomass. Therefore, stirring the biomass
with water in an open tank would oxidise the easy-to-digest material into
carbon dioxide and water. If you spent too much time on stirring, only the
difficult-to-digest material would enter the anaerobic digester and your
biogas yield would be rather low. My advice would be to introduce food
waste and kitchen waste directly into the anaerobic digester and subject
only the fecal matter to mixing under aerobic conditions.
Yours
A.D.Karve



On Sun, May 20, 2012 at 7:59 PM, Deepak D. G. <ghindwani at gmail.com> wrote:

> Dear expert,
>
> I am planning to build Floating AD (about 4 to 6 m3) using three inputs:
> Goat Waste, Human Waste and Kitchen Waste.
>
> As far as I understand, because of the human toilet system - it makes the
> human waste has too much water. While, I think goat waste is very dry
> (little water) and kitchen waste is very easy to premix with water.
>
> With that understanding, can I just combine all wastes into one chamber
> and feed them  directly  to the digester.?
>
> I have this  idea is to combine all the  waste into one small water tank
> (may be 100 liter or smaller ) and the overflow is fed into a brick well
> with floating plastic gas collector. Do you have any suggestion how to make
> the handling of the waste easier with minimum human interaction?
>
> Does any body have done the same thing or similiar?
>
> Regards,
> Deepak
>
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>
>


-- 
***
Dr. A.D. Karve
Trustee & Founder President, Appropriate Rural Technology Institute (ARTI)
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