Saturday, January 3, 2009

Backyard Biodigester, Batch 2

You know you have a tolerant wife when she lets you bring in a 55 gallon barrel into the kitchen. What's more, she let Jono and I fill it with food scraps as part of an experiment. I'm testing my backyard biodigester again.

A biodigester is a simple device: just a sealed chamber full of just about anything that was once alive (such as meat, vegetables, flour, leaves, or poop) and water. These ingredients are consumed by bacteria with a byproduct of methane gas (CH4).

Methane, of course, is combustible, and can be used for cooking, burned for light, or fed into an engine to produce electricity, pump water, or other useful purposes. The only hitch is the digestion process only works in an oxygen-free environment. And in case you haven't noticed, Earth has got oxygen, like, all over the place.

We were cleaning out the refrigerator, so I says to myself, self let's make some gas. The first thing to go in was a jar of pickle juice with a few bits of pickle afloat and seemingly unaware of their immanent sacrifice in the name of science. Then I put in some old raisins that were all stuck together, and some nuts. I chopped them all up in a blender first to liquefy the "feedstock" as much as possible. This is because bacteria don't have teeth.
Next to go were some stale hamburger buns, old baked potatoes, and a few hot dogs of questionable age.

Some muffin mix, cake mix, and cornbread mixes went in easily. A little baking soda helps reduce the acidity which makes the bacteria happy so that they smile little toothless smiles.

I poured in some crushed potato chips and old V8 juice that we bought out of nutritional guilt, a guilt that proved insufficient to actually make us drink it.
The blender made a good paste out of a bag of old peanuts.

Jono helped me with this project. He told me to take a picture of him pretending to eat it. All jocularity, that one.

The food scraps filled the barrel to about 5 gallons. I added equal parts of water for a total volume of 10 gallons. Ready to rot. The 40 gallons of air will not be a problem, as it will be consumed by the first stage of digestion. As long as no new oxygen source is available, we should be growing bacteria like no body's business.
Then I put on the air tight cap and lugged it out into the back yard. It would probably work better in the house because it is winter. The bacteria thrive best between 45-108 F, and lately it has been getting colder than that at night. But you really can't ask your wife to keep a thing like this in the house, no matter how tolerant she is.

More gas news as it passes...


Emily said...

Thanks for stopping by my blog! I always enjoy new comments. And yes, I loved Peace Like a River. I thought it was beautifully written. Have you read Leif Enger's new book entitled So Brave, Young, and Handsome? It's supposed to be just as good.

Paul said...

Interesting! Questions if I may.

Under optimal conditions, how long before the process will be complete?

How much gas will you get from 5 gallons of material?

Orangehouse said...

Emily, I did not know about Leif Enger's new book, thanks. I will have to check it out!

Orangehouse said...

Paul, I'm not sure how much to expect from this mixture, but I do have some data on systems that use manure as feedstock:

Chicken manure, 6-13 cubic feet of biogas per pound of manure,
Hog, 4-8,
Cow, 1.4-4,
Municipal sewage (people manure), 6-9,
I think that using food scraps as feedstock produces higher yields than manure, but I don't have data for this. It makes sense, however, because during digestion, the body removes energy from food. So manure should be less energy-rich than food. So if I estimate that I have 30 pounds of feedstock, and it produces, say 10 cubic feet per pound, then I should yield about 300 cubic feet. That sounds high, but we'll see.

Each cubic foot of biogas, at atmospheric pressure, is 60-70% methane (CH4), 30-40% CO2, 1-10% H2, 0.1% CO, 0.1% O2, and a trace of HS4 (the smelly part).

Straight biogas yields about 650 Btu/cubic foot.

My source for this is Al Rutan's Biodigester videos, which you can find on the web. Check back for info as the digestion occurs. It should take about 30 days or so.

Grafted Branch@Restoring the Years said... it!

Interesting--I'm learning all kinds of things I didn't know there were to know from your blog. It's a good thing.

btw...the new V8 fruit/veggie drinks are pretty good.

Paul said...

Thanks for the reply. It's enjoyable finding new options and giving some of them a try.

Biogas is a viable option on the correct scale. I gave up on composting. I don't have enough material to put into a compost pile to generate the needed temperatures. Now, I bury our organic kitchen waste. It decays quickly, add nutrients to the soil and improves the soil structure. However, I would like to try a batch of biogas and actually put it to use.

Th Linn said...

Ok so this has long been a favorite subject of study for me and I would like to ofer a couple things. First a question, Is this the same design you say you build in rural areas around the globe? This said I would like both any opinion as well as any observations on my post to your Blog. this will be my first respounce to a blog so be nice. Have you seen any of the work on this subject out of the Old Mother Earth Magazines? primaraly the designs they observed being built and used in I beleive it was Japan. Their designs are based on a more natural design than many westerners. They build a concreat ball under ground and run the load lines into it at non parilel to Verticaly nor Horitontaly this proves inportant as they have found that by in putting the fuel stuffs at this combined angle to the body of the fuel inside the digester chamber it will self stir which they say causes the bacterias to work almost non stop from start of batch life till almost the end of about 6 months If I remember right. They also add a water pond over filter that protects from acsidental gas release and posible spontanious combustion when it mixxes with oxegen in proper preportions. I had the misfortune of experiancing this first hand in a house that had been empty for a prolonged period of time, where in the septic system had the pee trap in one of the lavitories evaporate dry. The resulting gas release blew the lid off the toilet tank and cracked the same.) They also said that by placing these systems under ground that the resulting insulation of the bio chamber alowed the decomposition to begin sooner as well as cook at a greater temperature over the life of the cook. These raised heat levels also had a added benifitial feture of killing many if not all of the usualy harmfull to humans perisights and this would alow them to be able to use human as well as any other bio digestable fuel stuffs. { As is not the case in many of the designs I have seen being built in the west}They claimed that the resulting liquid as well as semi-solid left overs taken out of these systems could be used on human food crops and had proven to be quite benifisal when used in this way. They were reporting a operational heat level in these systems that was high enough to be viable to be extractted for heating uses for heating living spaces, water and such ideas. I had the isea that sences they said these systems were heating up and you needed to build ponds over them, that it might be viable to rais cat fish or other such feeder stock, for human consumption or resycling back into the feed stuffs for the system its self. They were useing tween chamber systems so as to maximise the systems use and stedy suply of all benifits. Just some ideas on the subject . Thanks for any feed back you can offer. also sorry for my spelling errors this dislexia is a real pain where I sit. Oh Another Idea I got from an artical in those old Magazines, you might find interesting was " How to grow a house? Yrs I said Grow!! write me at TAG z 333 9 @ ya hoo . com loose these spaces

Orangehouse said...

@Th Linn, no this is not the same design as the one I tried (unsuccessfully) to do in Honduras with fish manure. I have not done any others. I am not an expert, just a hobbyist when it comes to biogas. I have heard of some of the design features you mentioned and seen some of those ideas in a book called "A Chinese Biogas Manual" which is available free online. Those designs mostly use human sewage. I got the idea for this one from some good YouTube videos about biodigesters that use food scraps. There is a company making digesters for the Indian market.