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Energy

Methane Digesters (Small)

Methane digester

Agricultural, industrial, and human digestion processes create an ongoing (and growing) stream of organic refuse. Without thoughtful management, organic wastes can emit fugitive methane gases as they decompose. Methane creates a warming effect 34 times stronger than carbon dioxide over one hundred years.

One option is to control decomposition of organic waste in sealed tanks called anaerobic digesters. They harness the power of microbes to transform scraps and sludge and produce two main products: biogas, an energy source, and solids called digestate, a nutrient-rich fertilizer. The digestion process unfolds continuously, so long as feedstock supplies are sustained and the microorganisms remain happy.

Anaerobic digestion is used in backyards and farmyards around the world, and that use is on the rise. Small-scale digesters dominate in Asia. More than 100 million people in rural China have access to digester gas, which is used for cooking, lighting, and heating. In fact, during his years in ancient China, Marco Polo encountered covered sewage tanks that produced cooking fuel.

Biogas can reduce demand for wood, charcoal, and dung as fuel sources and therefore their noxious fumes, which impact both planetary and human health. Digestate enriches home gardens and small agricultural plots.

References

Alessandro Volta…“air from marshy soil”: Wolfe, Ralph S. “A Historical Overview of Methanogenesis.” In Methanogenesis: Ecology, Physiology, Biochemistry & Genetics, edited by James G. Ferry. Dordrecht, The Netherlands: Springer Science+Business Media, 1993.

methane in a pistol: Sethi, Anand Kumar. The European Edisons: Volta, Tesla, and Tigerstedt. New York: Palgrave Macmillan, 2016.

scientists [discovered] microbes were responsible: Wolfe, “Methanogenesis.”

methane [vs.] carbon dioxide: Myhre, Gunnar, Drew Shindell, François-Marie Bréon, William Collins, Jan Fuglestvedt, Jianping Huang, Dorothy Koch et al. “Anthropogenic and natural radiative forcing.” In Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, UK, and New York: Cambridge University Press, 2013.

[history of] organic waste as an energy resource: Insam, Heribert, Ingrid Franke-Whittle, and Marta Goberna, eds. Microbes at Work: From Wastes to Resources. Heidelberg, Germany: Springer, 2010.

[use in] Germany: Buckley, Pearse, ed. IEA Bioenergy Annual Report 2015. Dublin, Ireland: IEA Bioenergy Secretariat, 2015.

rural China…digester gas: REN21: Renewables 2016 Global Status Report. Paris: REN21 Secretariat, 2016.

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Errata

p. 26

Correction: The cumulative result: 10.3 gigatons of carbon dioxide emissions avoided at a cost of $217 billion.

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