| Right! In fact, all of these answers are right! Global warming -- Methane is 23 times times stronger (for a given weight, averaged over 100 years) than carbon dioxide as a greenhouse gas. Since one molecule of carbon dioxide is 2-3/4 heavier than a molecule of methane, it takes 11 methane molecules to equal the weight of 4 carbon dioxide molecules . When you adjust for this fact, it shows that methane is, molecule for molecule, a little over 8-1/3 times more powerful as a greenhouse gas than carbon dioxide. Therefore, every molecule of methane that is trapped and used for energy, releasing a molecule of carbon dioxide afterwards, not only makes the methane a renewable fuel, it also prevents the 8-1/3 greater greenhouse effect that would have happened if the methane had been released unchanged into the atmosphere. Where does methane come from? Houweling et al. (1999) give the following values for methane emissions [http://www.grida.no/climate/ipcc_tar/wg1/134.htm#4211]: Methane (CH4) emissions (Tg/yr -- note: Tg = "teragrams" or trillion grams) You can see that the total methane emissions per year is about 620 Tg. The contribution from livestock (overwhelmingly from cattle) is about one fifth of that total output, and more than a third of all methane released by human activity. Manure odor problems -- The complex brew of gases released by manure in a livestock manure lagoon creates a powerful odor in the surrounding environment. An enclosed methane digester uses anerobic bacteria to consume most of those chemicals and create the methane fuel. Solids remaining after the digestion process have very little if any odor. Further drying renders a pathogen-free fibrous material that retains the nutrient value of nitrogen, phosphorus and potassium, and it can be used as fertilizer or even bedding (see http://www.auri.org/news/ainapr02/11page.htm). Improved farm profits -- Farm-based methane generators have been around a long time on a small scale, but environmental concerns, rising energy costs, and new technologies have been helping bring them more into the limelight. Some of Another link for agricultural methane production information (with more links) is http://www.mnproject.org/programs/energy_sub/farmbasedenergy.htm. Click here to visit this site now. |
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| It's likely that methane generation from livestock manure could only ever be a locally important energy resource for certain areas of Minnesota. But in a world economic environment that's changing the rules for both agriculture and for energy, methane generation is something that deserves a closer look, especially when we consider all the renewable energy resources as a complete picture. |
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| Natural emissions |
|
| Wetlands (incl rice production) |
225 |
| Ocean |
20 |
| Termites |
15 |
| Methane hydrates(frozen in permafrost and ocean beds) |
10 |
| Natural total |
290 |
| Anthropogenic emissions (caused by human activity) |
|
| Energy |
110 |
| Landfills |
40 |
| Livestock |
115 |
| Waste treatment |
25 |
| Biomass Burning |
40 |
| Anthropogenic total |
330 |