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Energy

Methane Digesters (Large)

This sewage sludge digester fermenter facility, sewage treatment plant works, produces methane biogas as a bi-product.

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.

When produced at industrial scales, biogas can displace dirty fossil fuels for heating and electricity generation. When cleaned of contaminants, it can be used in vehicles that would otherwise rely on natural gas. On the solids side, digestate supplants fossil fuel-based fertilizers while improving soil health.

Germany leads the way among established economies with nearly eight thousand methane digesters as of 2014—almost 4,000 megawatts of installed capacity in total. Adoption is increasing in the United States, including use at the waste water treatment plant for the nation’s capital.

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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