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methane digester question.  RSS feed

 
Kendra Nelson
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Sorry if this is not the right place for this, I wasn't sure where to put this question.

I have been doing research on different toilet/septic options. I know Paul is a big fan of the composting toilet, or tree bog toilet, but what are the feelings about methane digester? My understanding is, and i could be wrong, that you collect your poo, and it goes in to your digester, and is digested by bacteria, to produce methane gas that is then captured and used for cooking fuel, heating, and for your hot water heater. At some point you have poop kol-aid that comes out that as been digested and can be directly added to your compost pile. Is this a correct interpretation? This seems like a great system to me, you get fuel and compost, but i would like to hear pro and con of this system from anyone who knows, and comparisons of this to other waste management systems.
 
Abe Connally
Posts: 1502
Location: Chihuahua Desert
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you will have to heat the water a bit to mix with the humanure. Also, to produce enough gas to be useful, you are going to need a lot of humans, one or two won't produce much gas.

Now, if you had a pig or 20 chickens or something like that, as well as kitchen waste and humanure, you might be able to produce enough gas for cooking.

You really need to keep the temps of the digester around 90F, so you need to include a way to do that.

For humanure, I would do a flow-through design with a retention time of at least 60 days, and then hot compost the effluent, just to make sure you get all the nasties.
 
Kendra Nelson
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Thank you for the info, i'll continue to research this topic.
 
Hanley Kale-Grinder
Posts: 112
Location: Mountain West of USA, Salt Lake City
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As mentioned...imo this involves to much infrastructure for just a few people. If implemented on a community wide scale or as a way of capturing some outside waste stream it starts to make sense.
 
Joshua Chambers
Posts: 71
Location: the state of jefferson - zone 7
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I have been researching this subject heavily in the last couple of years and designing a system for a community house we are planning. Apparently China has seven million of these household scale digesters, and India hundreds of thousands. The basic digester design is fairly straightforward though expensive no matter how you cut it, but hey so is a septic tank, which a digester rather resembles, except that the purpose of a septic tank is to settle the solids and not so in a digester. My design will use the "Sol Viva" (from a book by that name) compost bin design to process the outflow from the digester with a sealed worm bin lined with a think layer of wood chips to filter and process the solids and then a constructed wetland, leach field or other method for processing the black-water. Also, other inputs will be needed, as my research shows that human toilet flushings alone (flush toilets are a perk if that's your inclination!) do not contain sufficient carbon for efficient methane production, so not only would we need a lot of shit, but also added carbon, which we will add from an external loading port as sawdust or other agricultural "wastes". Also, I plan to use the perk of "garbage disposals" in the kitchen sink to eliminate taking out the compost while grinding the compost for ease of digestion!

I'm very excited about this system, and have it's construction hopefully in two summers.
--Joshua
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