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General Studies I

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2008 Paper

Question
53 out of 150
 

Consider the following:

1. Rice fields

2. Coal mining

3. Domestic animals

4. Wetlands

Which of the above are sources of methane, a major greenhouse gas?



A 1 and 4 only
B 2 and 3 only
C 1, 2 and 3 only
D 1, 2, 3 and 4
Ans. D Apart from gas fields an alternative method of obtaining methane is via biogas generated by the fermentation of organic matter including manure, wastewater sludge, municipal solid waste (including landfills), or any other biodegradable feedstock, under anaerobic conditions. Methane hydrates/clathrates (icelike combinations of methane and water on the sea floor, found in vast quantities) are a potential future source of methane. Cattle belch methane accounts for 16% of the world’s annual methane emissions to the atmosphere. The livestock sector in general (primarily cattle, chickens, and pigs) produces 37% of all human-induced methane”. However animals “that put their energies into making gas are less efficient at producing milk and meat”. Early research has found a number of medical treatments and dietary adjustments that help limit the production of methane in ruminants.

Industrially, methane can be created from common atmospheric gases and hydrogen (produced, for example, by electrolysis) through chemical reactions such as the Sabatier process, Fischer-Tropsch process. Coal bed methane extraction is a method for extracting methane from a coal deposit, while enhanced coal bed methane recovery is a method of recovering methane from an unminable coal seam.

Until now, it has been assumed that biogenic methane is formed anaerobically, that is, via micro-organisms and in the absence of oxygen. In this way, acetate or hydrogen and carbon dioxide are transformed into methane; they themselves are created in the anaerobic decomposition of organic materials. The largest anoxic sources of methane are wetlands and rice fields, as well as the digestion of ruminants and termites, waste disposal sites, and the gas produced by sewage treatment plants. According to previous estimates, these sources make up two-thirds of the 600 million tonnes worldwide annual methane production.

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