[Digestion] Digestion Digest, Vol 2, Issue 33

Anand Karve adkarve at gmail.com
Sat Oct 16 20:37:23 PDT 2010


Dear Mr. Kasulla,
thanks for the compliments. In spite of your request for specific answers to
specific questions, I must give you some background information. The
discussion of this particular theme started when I made a statement
that ARTI biogas system was primarily aimed at getting biogas whereas the
aim of other systems was waste disposal. We look at biogas as our primary
product, and therefore,we want as much of the feedstock to get converted
into biogas as possible. In the traditional, dung based biogas plants, only
about 5% of the dung gets converted into biogas, while the rest comes out in
the form of slurry, which is waste in another form. To make it palatable to
the users it is touted as a good organic manure. My statement resulted in a
request from Alexander Eaton to elaborate how our system worked. I therefore
explained the premises on which I had based my particular biogas technology.
It was from this point of view that you should look at my statements. In our
work we found that VS had no relevance to the amount of biogas produced. So
we started looking for another parameter that was more reliable, and we
found that digestibility of a product was more closely correlated to biogas
production. Sugar, starch, proteins and fats are mentioned in the textbooks
to have a high degree of digestibility, and we found in our experiments,
that these substances were generally completely converted into biogas. In
short, if you introduced into a biogas plant about 1 kg (dry weight) of food
waste comprising these substances, you would get about one kg biogas. In the
case of grass and green leaves, the digestibility is reported to be about
10%. We get about 90 to 100 litres of biogas from 1 kg green leaves, a value
that is very well correlated with the digestibility. Therefore, if anybody
asks us if a certain substance could be used as feedstock, we look at the
digestibility of the substance and not at its VS.  We get along very well
with our research without considering VS at all.
Now we come to your query about the dung. You have to agree that dung is not
digested by the methanogens. At least in the case of cattle feeding on plant
based fodder, dung consists mainly of lignin, which neither the animals nor
the microbes in the gut can digest, and microbial biomass. Most textbooks
tell us that there is a chain of microbial reactions, through which the
feedstock passes. The last lik in this chain is acetic acid, which is
converted into methane and carbon dioxide by the methanogenic bacteria. This
reaction takes about 40 days and only about 5% of the dung gets converted
into biogas. It is on this basis that I claim that dung is not the food of
the methanogenic organisms. You have accused the methanogens to be very slow
in their metabolic activity. They are slow, if you feed dung to them. But
they are extremely fast if you feed them with sugar or starch. In fact, in
the case of sugar, we start getting combustible biogas just 2 hours from the
time of introduction into a biogas plant. Saying that dung is the food of
the methanogens, is like saying that manure is the food of humans, because a
chain of biological reactions in the field results into the conversion of
manure into the food that we eat.
The C/N value is a ratio. It is neither the value of C nor of N. Textbooks
say that this ratio should be between 20 and 30. In our practice we have
been able to get good results with material having a very low C/N ratio, the
vlue being lower than 10, and often even as low as five.
Yours
A.D.Karve
On Sun, Oct 17, 2010 at 3:15 AM, Srinivas Kasulla <srinivaskasulla at gmail.com
> wrote:

> Dear Dr Karve,
> We are really proud of you being an INDIAN and making the entire Nation
> proud with the work you have done in the field of Biogas/Anaerobic digestion
> in India, but after reading some of your views it has confused me very much
> and even after 2-3 days of continuous research ONLINE and going thru some
> books i could find some of the answers for the data you have mentioned
> earlier, I would appreciate if you clear my doubts:
> 1) As am into this field from quite a long time but not as much as you have
> been and whatever you have mentioned about TS, VS, Cowdung, BOD etc is
> making me so confuse that it seems that i have to start from the basics and
> all my knowledge which i have accumulated till date will be waste.......
> you have mentioned that VS and BOD - neither of these are corelated to
> quantity of biogas generated?
> you said digestibility of the feedstock is to be considered for biogas
> generation? if not TS? if not VS? if not BOD? then what is this
> digestibility of the feedstock?
> I can agree that the mistake is to expect the same biogas yields per kg of
> VS or of BOD from a different feedstock may vary.
>
> 2) You have mentioned that DUNG cannot serve as a food for the methanogens
> because they are THROWN OUT of the body alongwith the dung??
>
> 3) The methanogens in the dung are very slow workers and they need
> retenntion time which we give in the digesters and which is missing (the
> number of days for holding - the gut of an animal is limited). the
> methanogens in dung keep on working even when the dung is thrown out of the
> body, and the process becomes slow due to exposure to the oxygen and once
> again they start producing the methane when they are put inside the
> digester........
>
> 4) you have mentioned that the FETISH C/N values should be discarded? how
> can I DISCARD THESE VALUES AND RATIOS? can you please teach me to discard
> the C/N values from my digesters? and you have mentioned the C/N values to
> be 10 or 5 but is it for C or for N?
>
> would be eagerly waiting for your answers to the above questions only, as
> in my earlier few mails i have asked you certain questions and had received
> answers from different experts in the blog and have received some answers
> from you which were not at all connected to my questions.
>
> with warm regards
> SRINIVAS KASULLA
> +91 9004689601
>
>
> On Sat, Oct 16, 2010 at 12:30 AM, <
> digestion-request at lists.bioenergylists.org> wrote:
>
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>>   1. Re: Attachment to previous Article - More scientific based
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>> ----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Fri, 15 Oct 2010 12:37:37 +0800
>> From: Anand Karve <adkarve at gmail.com>
>> To: For Discussion of Anaerobic Digestion
>>        <digestion at lists.bioenergylists.org>
>> Subject: Re: [Digestion] Attachment to previous Article - More
>>        scientific based research and questions
>> Message-ID:
>>        <AANLkTinPEb_k_6gu06EaKu0QPs7zJnuKJ+QjFcoT0KAh at mail.gmail.com<AANLkTinPEb_k_6gu06EaKu0QPs7zJnuKJ%2BQjFcoT0KAh at mail.gmail.com>
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>>
>> Dear Alex,
>> I give below the philosophy of our biogas work. Our first assumption is
>> that
>> because the methanogenic archaea reside in the guts of animals, they eat
>> what the animals eat. Our second assumption is that these organisms are
>> universally found in the fecal matter of animals because they are thrown
>> out
>> of the body along with the dung. Therefore we do not accept that dung
>> serves
>> as food for the methanogenic archaea. In fact, it is mentioned in the
>> textbooks on biogas technology that several species of bacteria are
>> involved
>> in reducing the dung to acetic acid and that the methanogens turn the
>> acetic
>> acid into methane. Our third assumption is that using the terms VS and BOD
>> to describe the feedstock are wrong. Neither of these parameters is
>> correlated with the quantity of the biogas generated. The use of these
>> parameters in biogas work is comparable to using the phlogiston theory in
>> chemistry. We therefore propose that digestibility of the feedstock be
>> considered as the correct parameter to describe the feedstock. Methods are
>> available to determine the in vitro dry matter digestibility (IVDMD) and
>> these values are available in books on cattle fodder. We ask the users of
>> our biogas plants to ask themselves the question if the feedstock would be
>> digested by animals. If the answer is yes, it is the right feedstock. We
>> also feel that the fetish of C/N ratio should be discarded. We have
>> operated
>> our biogas system for months on end, using only green leaves, or oilseed
>> cake, which have a C/N value of less than 10, some time as low as 5.
>> We make only sparing use of a biphasic system. In fact, my advice is to
>> avoid the use of a biphasic system. In a biphasic system, in order to
>> break
>> down the difficult to digest material, one makes use of an aerobic
>> fermenter. In this phase, a lot of the easy to digest material, which
>> would
>> have yielded methane in the anaerobic phase, is lost, being converted into
>> carbon dioxide.
>> You can now understand, why the biogas workers hoot me out and don't
>> believe
>> in me.
>> Yours
>> A.D.Karve
>>
>> >
>> >> On 07/10/2010 01:39, Alexander Eaton wrote:
>> >>
>> >> Dr Karve,
>> >>
>> >> Your innovation and work in the field is quite appreciated, and your
>> >> system really opens doors for us who are also not technically focused
>> in the
>> >> biology of biogas, but rather its application to families and
>> communities.
>> >> That is why it seems your use of food waste and loading rates based on
>> gas
>> >> production for a family really widens the populations we may be able to
>> work
>> >> with globally.  Do you have a paper or document that has this data and
>> other
>> >> user data available?
>> >>
>> >> Best,
>> >>
>> >> Alex
>> >>
>>
>
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>


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

*Please change my email address in your records to: adkarve at gmail.com *
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