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Biogas Q + A

How does a wastewater system produce usable fuel?

The average person in the U.S. creates about 100 gallons of wastewater every day. This wastewater must be treated and purified before it can be reintroduced into the environment.

The decaying of organic materials in wastewater produces methane gas as a by-product. This gas can be converted to energy by co-firing it with coal or using it as a substitute for natural gas.

How is the methane gas captured?

Methane gas for Green Power Switch comes from the city of Memphis wastewater treatment plant. The plant’s lagoon is covered to capture the methane, which otherwise would have to be burned off in order to reduce the danger that comes from gas buildup. The gas is captured and piped to Allen Fossil Plant, where it is burned in the boilers along with coal.

How does co-firing methane with coal help the environment?

If methane is released directly into the atmosphere, it is a potent greenhouse gas. In fact, its global warming potential is 21 times greater than that of carbon dioxide. Burning it to produce electricity dramatically reduces its global warming impact. In addition, because it replaces coal, it helps reduce emissions of sulfur dioxide and nitrogen oxides, which contribute to acid rain and global warming.

TVA’s use of methane fuel eliminates the consumption of more than 20,000 tons of coal per year. Producing electricity from methane avoids the need to use coal, a nonrenewable resource, to produce the same amount of electricity. The project provides 8 megawatts of power production.

Can this form of renewable energy be expanded?

Burning methane to generate power can be done either in new, dedicated combustion systems or by retrofitting older coal units. Because of TVA’s years of experience with coal generation and the comparatively small investment required to retrofit coal plants, co-firing methane in coal plants is a practical way for TVA to increase the generation of renewable power.