[Stoves] Heat destroys Jatropha toxins Re: jatropha, stoves, and biochar.

Fri Jan 28 16:46:43 CST 2011

>From David House in response to some comments on this list.

Regards

Crispin

++++++

Dear David

Any ideas here? I don't want to bother you with asking to join in the
conversation, it is not that interesting, but the from following you might
have something to say.

I appreciate the invite, but I'm just too busy to engage much. This is one
reason why I don't always respond even in this forum...

Biomass briquettes are normally made from very liquid retted material. If
the liquids from the digester were taken off and the fibres remaining
briquetted, it may suit everyone.

There is good literature about de-watering slurry and making bedding
material, a use which likely shares a good many process steps with making
briquettes.

The discussion on what is left in jatropha as toxins after digestion or
heating stalled when everyone agreed no one knows the next answers.

It sounds as though the distinction between toxic and toxic to who or what
was not clearly made in the discussion. Dihydrogen oxide is toxic in some
conditions. Oxygen is toxic to obligate anaerobes. One of the better papers
regarding the pertinent chemistry of Jatropha is "Agroclimatic Conditions,
Chemical and Nutritional Characterization of Different Provenances of
Jatropha Curcas L. from Mexico"(
http://www.eurojournals.com/ejsr_39_3_08.pdf). Although again it's negative
evidence, considering its aims, I think it can be taken as significant that
this paper mentions composting Jatropha without indicating any problems:

In some places in Mexico, J. curcas has been intercropped with beans,
peanut, chilli, coffee, medicinal and aromatic plants for the first two
years, giving additional productive outputs. In addition, J. curcas fruits
are used as compost or to generate biogas.

Likewise, the Institute for European Environmental Policy (Nele Bunner,
author), in a paper about biofuels in South America (here
<http://www.gotaverde.org/userfiles/file/D51a%20-%20Final%20Report%20IEEP_EN
.pdf> ), says that

Independently from the production model, all projects make use of the
possibilities that Jatropha offers to improve soil quality. Among the
practices taken to keep or further enhance the soil quality many projects
leave primary material (leafs and tree-cut) on the fields instead of
collecting them. The resulting biomass provides micronutrients directly on
the field. Concerning other residues from processing, most projects claimed
that they can make use of all parts harvested from the Jatropha plant.
Projects which already had a substantial harvest said that all the material
was reused in some stage of the plantation cycle. One project developer
explained the detailed analysis they undertook of the residues. After
harvesting the fruit, opening and pressing it, the hull can be used
two-fold: to produce organic briquettes (3kg briquette has a calorific power
of 1 kg fossil oil), or as a fertilizer. For the latter one it was grinded
and composted anaerobically and became a very good fertilizer (with NPK, 15%
each). This project further analyzed the seed cake which they tested for the
use of three different purposes: when the cake is detoxified it can be used
for animal feed with 56% protein, it can be used as a biopesticide and as
fertilizer.

If the Jatropha curas L. in question were the most common toxic variety, I
would not burn the seed cake until exhaustive analysis had demonstrated to
me that no toxins were present in the smoke from a poorly combusted fire.
The reason is two-fold. Of course if it is well and completely burned as it
would be in a well-designed stove, then analysis of the smoke might
demonstrate safety. However, as soon as it becomes known as a fuel, it is
bound to be used in all kinds of stoves, and not just those which are
well-designed. And the second reason is that if I would not expose my
grandchild to it, then I could not in conscience advocate its use. And given
that, for example, Jatropha has some carcinogens in it, it would take a lot
to convince me that it was safe not only according to present tests, but
safe beyond what might presently be demonstrated: again, absence of evidence
is not evidence of absence.

No question, small children are exposed every day to toxic smoke products.
That is regrettable and another excellent reason for your work. Taking
action that might add to that toxic burden strengthen that tragedy, and
unless there are really compelling reasons for it-- which I don't think
there are, since the better part of the energy from the seed cake can be
harvested through biogas-- I would not want to take a position that might
inadvertently exacerbate existing or cause new problems.

d.

-- 

David William House

"The Complete Biogas Handbook" www.completebiogas.com

Vahid Biogas, an alternative energy consultancy www.vahidbiogas.com 

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