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using aerobic process to heat anerobic digester?

Posted: Mon Feb 02, 2009 10:05 am
by davidwillis
I am working on my plan for an anaerobic digester, and just got to thinking, it may be easier to keep it heated directly by aerobic digestion. This may be simpler than burning methane to heat the digester.

I have two ideas, the first one would be the easiest, but I am not sure if it would work, or if it would kill the anaerobic bacteria.

Idea 1
introduce small amounts of air into the anaerobic digester to promote some aerobic bacteria into the digester. The more air you put in the more anaerbic bacteria, and heat produced. The temperature could be controled directly by the amount of air put into the digester. Sounds nice, but will the air kill the anaerobic bacteria, or will the aerobic bacteria consume it, and heat the digester without disterbing the anaerobic bacteria?

Idea 2
if idea 1 is not viable, I was thinking of having an aerobic digester on the outside of the anaerobic digester (have a tank inside of a tank). The temperature could be controlled the same as in idea number one, but the two bacteria would be kept seperate. I could possibly even use the spent material from the anaerobic digester to feed the aerobic digester, as I am sure there is still some undigested material left.

Anyway, just a couple ideas I was thinking about, and wanted to get some feedback.

Re: using aerobic process to heat anerobic digester?

Posted: Tue Feb 03, 2009 11:26 am
by Bob
Idea 1: ...will the air kill the anaerobic bacteria
Yes. It could also make a dangerous, potentially explosive fuel/air mixture. You don't want to do that.

Your Idea 2 sounds too complicated and expensive. (I would use all the organic material I had available to make biogas from, and focus my efforts on measures to reduce the demand for heat -- i.e. add insulation, heat exchange between inflow and outflow, and/or higher solids content, reducing the volume of water needed to be kept up to temperature.

Re: using aerobic process to heat anerobic digester?

Posted: Wed Feb 04, 2009 8:19 am
by davidwillis
Thanks bob... I didn't think about the explosive mixture!