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[greenyes] Composting, Methane, Nitrous Oxide, Carbon


In the interest of education I offer the following:

Research has shown that methane (CH4), a product of anaerobic (without oxygen) bacterial digestion, is approximately 21 times more efficient at trapping heat in the atmosphere than carbon dioxide (CO2). Similarly, research has also shown nitrous oxide (NO) to be approximately 270 times more efficient at trapping heat than carbon dioxide. Both are greenhouse gases like carbon dioxide but neither occur anywhere near as abundantly as CO2.

When accounting for greenhouse gases there is still disagreement on methods, however, the general consensus/agreement amongst researchers is that biogenic sources (sources that would be part of global biogeochemical cycles without human intervention) should represent neither a gain nor loss to the system.

Early modeling of biogeochemical cycles indicated that composting generally represented a net good. However, it has been suggested that these models were NOT complex enough! Compost piles, as it happens, are capable of producing CH4 and nitrogen oxides. How much is produced depends on a complex mix of composting practices including conditions, feedstocks, processes, moisture content, etc. The amount of carbon sequestration and pesticide offset is not clear either. At the moment, there is no agreement on just what is the "average" compost process and other parameters, and the question has been raised as to whether or not the average process can even be modeled.

As was pointed out elsewhere (T. Evans (2005). US Composting Council Compost Discussion List)), if carbon (from decaying organics) in a compost pile is converted to CH4 or nitrogen (N) is converted to NO2, it represents a "new" form or addition to the system. Plants take up carbon as CO2 and N as NO3. They do not take up the greenhouse gases CH4 or NO2. The intake - release ratio is 1 to 21 in the case of CH4 and 1 to 270 in the case of NO.

References:

Peigne, J. and P. Girardin (2004). "Environmental impacts of farm-scale composting practices." Water, Air, and Soil Pollution 153(1): 45-68.

Zeman, C., D. Depken, et al. (2002). "Research on how the composting process impacts greenhouse gas emissions and global warming." Compost Science and Utilization 10(1): 72-86.


Stephan

--
Stephan Pollard
Environmental Dynamics Doctoral Program
University of Arkansas
Rm 113 Ozark Hall
Fayetteville, AR 72701
Tel: (479) 479-6603
Http://www.cast.uark.edu/~sp



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