[Digestion] biogas from restaurant oil & food waste

[Anand Karve]

Dear Mr.Zschech,
any biogas plant would be able to accept the fatty material as
feedstock. You may have to conduct some experiments to determine the
quantity to be introduced daily. Castor beans, for instance, contain
about 50% oil. We have been able to use about 1g macerated castor
beans per litre of digester capacity in our ARTI biogas system, which
yielded  A biogas plant is an open system, which harbours different
kinds of micro-organisms. If you introduced more  feedstock than the
optimum quantity, the unused feedstock would be consumed by the other
organisms. If they are allowed to multiply their numbers, the system
suffers a break down. A biogas plant is also susceptible to
temperature. When it is cold, the gas production gets reduced. Novices
feel that they should increase the feedstock quantity in order to get
more gas. But that is a wrong notion. Low biogas production under cool
temperature means that the organisms are eating less. One should
therefore reduce the feedstock quantity proportionately.
Yours
A.D.Karve

On Wed, Oct 5, 2011 at 3:47 PM, Wayne Zschech
<waynezschech at calvarychapel.com> wrote:
> G'day All!
>
> The waste vegetable oil we collect from the restaurants has up about 10-12%
> water and food waste in it.  We heat the oil up to 65oC and then drop this
> 'soup' out from the bottom.  We want to utilize this waste about 1,5-2,0
> tonnes per month as a feedstock for biogas production.  We also end up with
> about 500kg of rancid fats/oils that we can't use for biodiesel production.
>
> I understand that both the soup and the rancid fats should be able to give
> me lots of gas but don't know how to calculate the needed reactor volume.
> I'm also concerned that the fat will float at the top of the reactor and
> cause problems. Could anyone give some reactor design tips for these
> feedstocks?
>
> Also is it possible to produce a digestate that can be used as animal feed
> or feed supplement?  from this waste? from restaurant food waste in
> general?  We have long winters and I don't want to have to store the
> digestate as fertilizers for many months if I can produce a product local
> pig farmers can use.  It has been suggested that I should make batch type
> reactors so as to be sure that all the organics have been digested before
> 'packaging' or storing it.  Are pathogens likely to be a problem?  Should I
> consider thermophilic temperatures? I've read that heating such waste to
> 70oC for 1 hour is the industry standard.
>
> What other problems can I expect to encounter.
>
> Any input would be appreciated.
> Many blessings,
> Wayne
>
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> http://www.adelaide.edu.au/biogas/
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>
>
>



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