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Name:  Sarah M.
Status: educator
Age: 20s
Location: N/A
Country: N/A
Date: 10/24/2004


Question:
Hi, We have been unsuccessful in our attempts to capture methane gas from decomposing organic material in our lab activity that is designed to simulate the process of how Natural Gas is created. We have used fruit, vegetables, grass clippings, and dirt collected in an empty water bottle covered by both a balloon and a lab glove. The balloon and glove have been secured with duct tape. While the ingredients have been decomposing, our balloons have not been inflating. Do you have any suggestions for us that would help in the success of our lab?


Replies:
Sounds like a little too much uncertainty for me to pin it down. It may also be a large program to get successfully started, even if it is considered technologically quite doable.

- Duct tape, while strong, is not known for making air-tight joints. Somehow you will need to prove that your balloon-and-bottle assemblies have no slow leaks.

- Methane, in addition to being a gas like air, is a hydrocarbon like oil or propane. Rubber is a hydrocarbon too. So methane has a higher solubility in rubber than does air. So methane will leak out through the walls of a perfectly intact balloon faster than will air. Air itself would only last about a week. So you would need to be filling your balloon with methane in something like two days. That is pretty brisk for bio-generation, even if you knew it was operating properly. So I would suggest starting with a silvery Mylar balloon, because the aluminum on its plastic will stop methane for a month or more. Lab gloves will vary depending on their material, but they generally are not nearly as good as Mylar.

- When you have methane running, you might consider capturing the methane by running a tube to the bottom of a jug of adsorbent, such as activated charcoal or zeolite molecular sieve. These are gritty, porous granules with very high surface area that can grab the methane while letting air pass through. And no perfect seal would be necessary. Then later you would release the methane by warming the bottle or granules, and perhaps briefly demonstrate a dense enough stream to run a gas flame.

- Imagine you are about to become a maker of cheese or yogurt. You are in an experimenting phase, trying develop a culture, trying to find, capture, isolate, and mass-produce a good micro-organism for generating methane from your particular raw materials in your conditions. Not so many bugs will qualify for your use. And those that do qualify must be given the right fuels and conditions. Many bacteria do not make methane, and many that make methane will not do it from your materials, or will not do it in air or at your temperature, or will not bother with the low-energy methane reaction if they have the fuels they need to run a higher-calorie reaction they know of.

- we know cows definitely make some methane, so include some (10%?) fresh cow manure. Maybe that will successfully seed your "culture" or breeding program.

- we know swamps sometimes make methane. The silty, stinky mud at the bottom of many swamps is definitely anaerobic and can only be making methane. It does not have any air to burn. The muck is thick enough that it never gets new oxygen stirred into it from the water above, and it is loaded with micro-organisms which compete to quickly use up what little oxygen reaches them. Get some of that mud, maybe a lot of that. The bacteria there are a known positive, and even the surface area of rock-particles in the mud can be useful as mass homes for the bacteria. provided enough of the right food is slowly circulated within it. For this muck you know it can bio-generate while fully submerged in water, so your food can be homogenized in a blender, and probably should be for fastest action. Later when you have it operating in larger batches for longer periods, you can omit the blender.

- If/when you do get a bottle making noticeable methane, never throw it all out, always keep some of the mash to seed other bottles. Maybe keep a collection of sealed, dried or frozen small samples as your program continues. You never know when you will want to go back to some previous good moment and start again from there.

- "pre-digest" your mix to get the bacteria going strong before you try to do collection. Cap the bottle with no balloon, and keep it warm to hot, and tumble it a few times a day for a few days. I would guess it needs to start smelling distinctly before it will be generating methane. Besides, a capped bottle is more likely to have all its oxygen used up, starting anaerobic behaviors. (assuming those are the good ones.) Your capped bottle might well need a long, very narrow tube to let pressure out.

- consider whether you have the best amount of water in your mix. Complete submersion might drown your bugs if they want oxygen, and too little makes it unlikely they will multiply, migrate, and feed fast enough. Water helps bugs with no feet get around to where the food is. I guess the pile should seem pretty wet but still have air-paths throughout. (I may be wrong about air-paths.)

- get yourself an inexpensive consumer-grade breath-alcohol meter. If you somehow draw a little of the bottle's air through it, I think it will react to the methane in the air just as it would to alcohol in breath. The advantage here is it can directly see < 1% methane in air, the kind of very small quantities you need to compare in order to quickly improve upon very low levels of generation. I'm sure there are flammable- or toxic-gas detectors from safety-equipment vendors which would do the same thing.

- do some literature searching and web-surfing and reading, about particular bacteria which make methane.

Look for what temperature they need, whether they need anaerobic conditions (absence of oxygen) to make methane, what food of mix of foods causes them to do that most strongly, and what their best or second-best generation rate is. You may find you cannot expect the contents of, say, a 1-pint bottle, to fill a modest balloon in 2 days. Large operating scale many be a big point in this business. If so, it makes it harder for you to get started successfully.

- I am wondering if sugar is perhaps less-than-optimal food for methane-generators.

Except when your are giving them air to let them multiply fast.

good luck-

Jim Swenson



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