[Digestion] [Stoves] Karve connecting Biochar and Biogas

[Duncan Martin]

Dr Karve's clarification of his original point is helpful - but I think it
still leaves some questions.

He implies that the stimulatory effect of charcoal is long-term and gradual,
so the mechanism isn't likely to be the absorption of a nutrient excess or
ant other inhibitors.

However, in this context, I'm not convinced by a role as a biomass support:

   1. Would the flow velocities in a digester be high enough to strip
   biomass off such a support medium? If not, it's hard to see a significant
   role as a source of inoculum. (Bear in mind that anaerobic filters are
   designed to retain biomass at much higher velocities.)
   2. The increased feed rate was 3kg (dry wt) per day, which implies about
   30L of food waste per day by volume (neglecting for the moment the free
   water in which it is suspended). In a 1000L digester, that implies a mean
   retention time of 33 days. (And a very long retention time of 100
days *before
   *adding the charcoal.) That implies a large volume of partly-digested
   solids for colonization by microbial flora. This would provide a major
   source of inoculum, so it's not obvious that charcoal would add
   significantly to it. (Yes, native charcoal has a massive surface area per
   unit weight - but that advantage would disappear if it was covered in
   biofilm.)
   3. In practice, the feedstock would probably be more dilute (depending on
   the digestion technology in use), so the retention time* would be reduced.
   However, it seems unlikely that the volumetric throughput would be high
   enough to negate the above arguments. (*It would be interesting to know what
   it was...)

Yes, Dr Karve's experiment allowed an increased feed rate and, as Crispin
says, the higher gas yield is a direct result of the larger volume of
"material ingested". However, that doesn't explain *how *the increased feed
rate became possible.

I would conclude that Dr Karve's observation remains unexplained - we
shouldn't jump to conclusions.

Duncan Martin PhD
Cloughjordan
Ireland


On 11 October 2011 17:21, Crispin Pemberton-Pigott
<crispinpigott at gmail.com>wrote:

> Dear Ron’N’All****
>
> ** **
>
> I think everyone involved in the gas business is clear that the production
> increase is the predictable results of a change in fuel (not grasses/dung)
> to high starch/sugar feedstocks.****
>
> ** **
>
> The increase in gas is not apparently the result of the char which is used
> more as a culture or host medium to ensure inoculation of the incoming
> feedstock. The speed of gas production is the result of the material
> ingested.****
>
> ** **
>
> Dr AD has been in communication with David House (author of the most
> important handbook on the subject) and everyone seems agreed on the basics.
> The producing increase by this means was demonstrated as long ago as the
> 1920’s.****
>
> ** **
>
> Regards****
>
> Crispin****
>
> ** **
>
> ** **
>
> *From:* stoves-bounces at lists.bioenergylists.org [mailto:
> stoves-bounces at lists.bioenergylists.org] *On Behalf Of *
> rongretlarson at comcast.net
> *Sent:* October-05-11 11:05 PM
>
> *To:* Anand Karve; gasification at lists.bioenergylists.org; Discussion of
> biomass; biochar; digestion
> *Subject:* [Stoves] Karve connecting Biochar and Biogas****
>
> ** **
>
> AD (cc four lists):
>
>     I have not previously seen the connection between Biochar and Biogas
> that you described (below) today on the gasification list.     In
> particular, you say you "..* filled the digester**
> with charcoal, my system accepted three times the normal daily input
> and produced three times as much gas.*"
> I think what you describe can be a very powerful push for both Biochar and
> Biogas.  Can you describe what you have learned a little more?
>
>      I know too little of digesters, so this is not clear.  I think I know
> your kitchen-sized inverted "barrel" gas chamber and think I understand the
> last part - of getting three times as much gas in the next 24 hours or less
> (and 3X is a huge change!).   Does the idea of accepting three times more
> mean essentially the same thing?  I would think you could "jam" any amount
> in;  what limits acceptance?
>
>     Do you agree that this is very important new information?  Do you agree
> this information could help speed up both technologies?  I believe there is
> wide agreement that Biochar benefits from added biological material (that
> would not be long-lived from a sequestration perspective).  Is there any
> reason to think that the traditional use of digester effluent for ag
> improvements will be in any way harmed if it is continued through the
> addition of carbon-negative Biochar?  Should this not promote sales of your
> charcoal-making stoves?
>
>    If I haven't asked quite the right question - please answer the right
> one.  And congratulations on learning and reporting this.
>
> Ron
>
>
>
>
>
> The remainder from AD Karve today on the gasification list:
>
>  There are a lot of very simple ideas that need to be tested.  I am
> currently working on increasing the efficiency of biogas digesters and
> feel that it might be possible to reduce the size and the capital
> expense of a biogas system. For instance, when I filled the digester
> with charcoal, my system accepted three times the normal daily input
> and produced three times as much gas.
>    < snip>
> Yours
> A.D.Karve
> ***********************************************
>
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> for more information about digestion, see
> Beginner's Guide to Biogas
> http://www.adelaide.edu.au/biogas/
> and the Biogas Wiki http://biogas.wikispaces.com/
>
>
>
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