[Digestion] R: biogas from restaurant oil & food waste

[Ing. Alessandro Francese]

Wayne,

why would you transform oil and fat into biogas when you can burn its
directly in commercial gensets to produce electrical energy( efficiency
36/38%)?

Alessandro Francese

 

Da: digestion-bounces at lists.bioenergylists.org
[mailto:digestion-bounces at lists.bioenergylists.org] Per conto di Wayne
Zschech
Inviato: mercoledì 5 ottobre 2011 9.47
A: digestion at lists.bioenergylists.org
Oggetto: [Digestion] biogas from restaurant oil & food waste

 

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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