Monday, March 24, 2008

Backyard Biodigester, Part I

If you recall from my earlier post, "Poop Power", I have been reading about the conversion of organic material into methane gas. As my wife, M, was not too keen on a barrel of sewage in the backyard, I looked for alternatives using food scraps. It turns out that in India, lots of urban digesters are being used in homes to turn food scraps into methane gas for cooking.

So I am experimenting with a simple digester using food scraps and yard waste. Let me explain...

This lovely mess is not a salad, but a five-gallon bucket full of wilted spinach leaves, left over Cheetos, stale hot dog buns, purple cabbage, and water.

I tossed these ingredients into the bucket and added some water.

In order for the methane-producing bacteria to thrive, they need carbon as well as nitrogen. The carbon is provided by the food scraps, the nitrogen comes from leaves and those "wormy" pollen pods from my Red Oak trees. They're all over the place at the moment on account of it being Spring.

Adding a couple of gallons of this stuff, and some discarded Easter egg shells, we now have a fine soup, reminiscent of the trash compactor scene in Star Wars Episode IV. "Shut down all the trash compactors on the detention unit!"

Now it goes in an air tight barrel. My homemade funnel didn't work very well, so I had to smoosh the stuff through the opening at the top. It made a mess big enough for me to be glad M talked me out of using sewage.

Next, we need to get a "culture" from the local sewer plant that contains the methane-producing bacteria. They go into the barrel and the lid closes it. As it sits in the sun, the bacteria eat the organic material and give off methane as a byproduct. One carbon atom from the food is joined with four hydrogen atoms from the water.

My hope is to learn "good recipes" for making methane in a third world environment. Methane can be used to cook, or even used as fuel in an electric generator. Anyone have any good recipes out there?


Robert said...

These pictures make me hungry.

Obie Tater

Redlefty said...

I actually produce a decent amount of methane myself some days!

Cool stuff!