Building a (one-stage) Anaerobic Digester

14 thoughts on “Building a (one-stage) Anaerobic Digester”

1. Methane is a powerful greenhouse gas.

   “Methane in the Earth’s atmosphere is an important greenhouse gas with a global warming potential of 25 compared to CO2 over a 100-year period. This means that a methane emission will have 25 times the impact on temperature of a carbon dioxide emission of the same mass over the following 100 years. Methane has a large effect for a brief period (a net lifetime of 8.4 years in the atmosphere), whereas carbon dioxide has a small effect for a long period (over 100 years). Because of this difference in effect and time period, the global warming potential of methane over a 20 year time period is 72. ” From Methane’s wikipedia article.

   I can appreciate the desire to help these people, but if anthropogenic climate change is actually a problem then this could be a disaster if widespread.

   Anyone have any thoughts on this?

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   1. I think the goal here (or at least one of them) is to burn the methane.

      When methane is burned it releases CO2. Obviously that’s also a greenhouse gas, but it won’t produce any more than was sucked out of the atmosphere in the first place to grow the “organic matter” you’re using as feedstock.

      Reply

   2. You’re quite right (though I can’t verify your figures) Methane is a more potent greenhouse gas than Carbon Dioxide.

      It is certainly important to burn the biogas otherwise you could argue that it’s doing more harm than good — but that’s the whole point of the exercise! FREE FUEL!

      À propos; Biogas is a variable mixture of Methane and CO2 – commonly around 60% percent methane but this depends on many factors.

      Reply

2. Also fun : Notice the improvised bucket and funnel in the picture.

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3. Doing this with dung is possible but the retention time — the length of time the dung needs to be in the system before it has released it’s potential biogas — is usually 30-45 days (depending on temperature and other factors).

   National Geographic Emerging Explorer, T.H. Culhane of SOLAR CITIES… http://solarcities.blogspot.com/ …is doing similar things but feeding the system with food waste — as inspired by Dr Anand Karve’s work at India’s ARTI Institute.
   http://www.arti-india.org/index2.php?option=com_content&do_pdf=1&id=45

   The retention time for a food waste fed digester is 2-3 days! and it yields more gas from much less feedstock and water input.

   (approx.) DUNG FOOD WASTE
   retention time 30-45 days 1-2 days
   feedstock 40kg 1.5kg
   water 40 ltrs 1.5 ltrs (at every feeding)

   It produces more gas, in a much smaller space, with much less feed – and you don’t have to handle dung!!

   SPREAD THE WORD!! ;)

   STOP PRESS… research work is being conducted into the use of cold-loving bacteria rather than the warm loving bacteria that are commonly employed. This would mean that these systems could be effectively and readily used by people in temperate climates rather than warmer climes.

   (I’ve tried hailing the makezine blog on this stuff before but to no avail. How about a post about it? – or a make magazine feature? This information needs spreading and there’s plenty of maker-spirit and ingenuity needed to move it forward!)

   Thanks.

   Marcel Lenormand

   Reply

4. Allow me to attempt to clarify that table a little (spaces got removed)

   (approx.)__________DUNG______/__FOOD WASTE
   rRetention time___30-45 days_/___1-2 days
   Feedstock__________40kg_____/_____1.5kg
   Water______________40 ltrs____/_____1.5 ltrs (at every feeding)

   (Here’s hoping the multiple underscores don’t get deleted!)
   [m]

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5. How do you transfer methane from tank spicket valve to another container.Say a usable bottled gas container to run a stove.

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