AD Thoughts

Digester design and construction info

Moderator: Bob

kjankows
Posts: 3
Joined: Mon Jan 28, 2008 8:10 pm
Location: USA

AD Thoughts

Postby kjankows » Mon Jan 28, 2008 9:38 pm

Ahoy Bob,

Just found your place and I think it is a great idea. I read through several forums regarding AD digestion systems and thought I might provide a little AD in-site, please comment and question I have limited experience in digesters of your size.

When digesting human waste, and basically all carnivores and omnivore waste, pasteurization is required to remove all those harmful pathogens before land application, please don't get sick. It may be best to send your effluent to the WWTP.

Anaerobic microbes take a long time to develop and mature, to optimize your system don't waste your solids, recycle! At the same time, maintain a VSS:TSS ratio of 0.8 or above, which will eventually require wasting your inorganic solids (which unfortunately are going to settle to the bottom), maybe sell or donate your wasted solids to your buddies to inoculate their digesters, or take a portion of your effluent solids and re-inject them into your digester.

On larger systems, mixing is extremely important (I'm talking about complete-mixed here not plug flow). This will provide a greater interaction between the food and microbes and prevent dead space to utilize the most of your tank volume. On plug flow systems, solids recycle are very important.

Heating is also important, 95 - 104 deg F for mesophilic methagonens. If you are using biogas to heat your water, why not wrap a portion of your water supply around your digester to recapture energy. Of course install a bypass when using cold water or when you really want a hot shower :).

Biogas... what a wonderful product. I see lots of people interested in using it for energy generation, however, when using it in a generator biogas conditioning is required to avoid maintenance issues (especially siloxanes) and nuisance gas emissions. This can get costly and may force you to use it only for heat generation. Remember, biogas is corrosive, make sure to use resistant tank and piping materials. The biogas to water interaction will also cause your pH to drop.

I also found this document online that gives a pretty good overview of anaerobic digestion from rural to industrial applications which is easy to read and will help answer many introductory questions:

http://www2.gtz.de/dokumente/bib/04-5365.pdf

Well those are some of my thoughts, please comment and correct me where necessary!

kjankows

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Bob
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Postby Bob » Sat Feb 09, 2008 7:24 pm

Hi kjankows,

(I just discovered your message, posted here almost 2 weeks ago -- but overlooked.)

Thanks for the insights -- and the pointer to the online pdf document. It looks excellent. (When I get a chance, I'll print it out and read it in detail.)

re comments and/or corrections, I appreciate your input. Glad you are here...
:)


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