Curtis,

On 8/21/2010 12:00 PM, lapg-request@arashi.com wrote:

Date: Fri, 20 Aug 2010 16:02:52 -0700
From: CURTIS BLANKINSHIP <curtis.blankinship@gmail.com>
Subject: [Lapg] methane digesters are the sh...t

This is a link to a small scale methane digester. the extra water tank is used to create pressure to use the gas for cooking or powering a generator. Does everyone get that we can produce power from our own excrement with very little pollution[?] This would get us back within earth's cycles...

The amount of biogas produced from one person's feces is about a cubic foot per day. Sewage digesters are designed with that figure in mind all over the world. A cubic foot of biogas is not enough to offer anything except a demonstration that burnable gas has been produced (that is, a cubic foot of gas will burn off in a few seconds).

That is not to say that making biogas is a bad idea; not by any means. Biogas is a more efficient means of turning biologically collected sunlight into energy than making alcohol or biodiesel. (Skeptical? See the chart at the bottom of this page. Acre for acre, biogas can out-produce alcohol by 800%!)

As far as a water tank creating pressure, actually the process that produces the biogas also pressurizes it, or at least provides enough pressure for cooking, lighting, and similar uses.

The digester shown in the video to which you directed us is actually too small (~55 gal) for real and practical use. (Figure that a digester that is properly fed and kept warm will create its own volume of gas every day.) You need a digester of at least 200 gal, for example, to get enough fuel for daily cooking. Putting four 55 gal drums together to get that 200 gal volume is not the best option, however. (Hard to heat, complex, relatively expensive.) A far better idea is to create a digester out of a plastic tube (these are found from sites on the web that sell shipping supplies, like ULine and Grainger's), sealed at both ends, with two pipes (inlet and outlet) and a gas outlet line. (A 40 inch dia plastic tube 12 feet long, when laying flat, will easily hold about 200 gal of digesting material.)

My next project is to build a larger digester (3,000 gal, 10 cu m) to utilize all the food waste from a local fast food outlet. I'm going to make it out of plastic sheets, of the sort used to cover greenhouses...

And by the way, I teach people how to make these digesters (in October, for example, there will be workshops in Hawaii and Pennsylvania), so please contact me if you are interested in learning more about it.

Be well.

David William House

"The Complete Biogas Handbook" www.completebiogas.com
Vahid Biogas, an alternative energy consultancy

www.vahidbiogas.com

"Make no search for water. But find thirst,
And water from the very ground will burst."

(Rumi, a Persian mystic poet, quoted in Delight of Hearts, p. 77)

http://bahai.us/