[Digestion] Attachment to previous Article - More scientific based research and questions

Paul Harris paul.harris at adelaide.edu.au
Thu Oct 7 15:09:27 PDT 2010


G'day All,

 

In the discussion below I see the term TS (Total Solids) used, and it is
important to remember that flour and sugar TS will be almost 100% VS
(Volatile Solids) and equate to very high COD per kg. It is VS/COD that is
available as substrate for anaerobic digestion, so when comparing other
substrates we really need a VS figure (or VS as % of TS) as a measure of
digestibility - manure VS is about 10% of TS so there will be huge
differences.

 

I also noticed in an earlier post the comment about methanogens being
present in our digestive tract (I agree that they are), but why? I think it
has been suggested they balance the H+ and H2 system so our digestive system
can operate (so they may be "good" bugs) but it may also be that we provide
an environment for their survival so they compete for nutrients. I know
CSIRO have done work on reducing methane emissions from cattle so I will try
to follow that up and I will also ask a gastroenterology colleague here as
well, but comments are welcome.

 

Happy digesting,

HOOROO

 

Mr. Paul Harris, Room S116b, Waite Main Building Faculty of Sciences, The
University of Adelaide, Waite Campus, PMB 1, Glen Osmond SA 5064 Ph    : +61
8 8303 7880      Fax   : +61 8 8303 4386
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http://www.adelaide.edu.au/directory/paul.harris

 

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From: digestion-bounces at lists.bioenergylists.org
[mailto:digestion-bounces at lists.bioenergylists.org] On Behalf Of Alexander
Eaton
Sent: Friday, 8 October 2010 3:30 AM
To: For Discussion of Anaerobic Digestion
Subject: Re: [Digestion] Attachment to previous Article - More scientific
based research and questions

 

Thanks All for the background documents.  These are extremely useful.  

Best,

A

On Thu, Oct 7, 2010 at 7:56 AM, David Fulford <davidf at kingdombio.com> wrote:

Hello Alex and Listers,

The best independent papers on the ARTI system are by EAWAG
(www.eawag.ch/organisation/abteilungen/sandec/publikationen/publications_swm
/
<http://www.eawag.ch/organisation/abteilungen/sandec/publikationen/publicati
ons_swm/index_EN#owm> ) who have also looked at the digestion of food
residues from markets in Kerala, South India. While food residues have an
average TS of 50% or less, Dr Karve bases his results on starch residues
(e.g. flour dropped on the floor from milling). Suich residues have a TS of
almost 100%. This means that we need to consider his gas production results
as per kg total solids, rather than per kg of wet material.

As the assessor from Ashden Awards who visited ARTI in 2006 (see
www.ashdenawards.org/winners/arti06), I had to evaluate Dr Karve's
statements.and his technology. The biogas plant uses simple cylindrical
drums, so there is nothing special about the design. The major difference is
the use of food residues rather than dung as the feed material. Since an
animal has used as much of the input energy in the food as it can before it
evacuates the rest, the gas production from undigested food is likely to be
much higher than that from dung. Processed food (flour, sugar and cooked
food) is likely to have a higher gas output than raw food, as much more of
the material is accessible to the microbes. There are several other biogas
projects in India using food residues as feed material, that started at
about the same time as the ARTI one. I have visited the first Biotech Ltd
project in Kerala (www.ashdenawards.org/winners/biotech) about which the
EAWAG report was written and another in Mumbai called the Nisargruna system
developed by BARC (see www.green-ensys.org/site/Biogas_Plant.html), which
uses a two-stage digestor design.
 
Looking at the basic thermodynamics of the process, it seems quite feasible
to generate 1 kWh of electrical energy from 1 kg of starch, as Dr Karve
suggests, although it does suggest a very high efficiency for the conversion
of starch to biogas. However, in practice, a 1 cu.m ARTI biogas plant is too
small to run an ic engine, as small ic engines are not very efficient.

Regards,

David Fulford 

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