Methane Recycling

Sacramento Regional County Sanitation District's (SRCSD) methane gas recycling program is just one of the ways SRCSD works to reduce impacts to the environment by innovatively reusing valuable resources. Methane gas or "biogas," a by-product of the solids digestion process, is used to produce steam and electricity at the Carson Ice-Gen Project, a cogeneration facility owned by Sacramento Municipal Utility District (SMUD) and located at the Sacramento Regional Wastewater Treatment Plant (SRWTP). Sending gas to the cogeneration facility for recycling purposes, instead of open flaring at the waste gas burners (which was the practice prior to 1996) greatly reduces emissions of air pollutants as well as greenhouse gases (GHG) from the SRWTP.

Power generated:

The SMUD cogeneration plant produces as much as 100 megawatts of power for local residential and industrial use, equivalent to the annual electrical usage by 150,000 households. The electrical power produced with the SRWTP digester gas equates to 4.3 megawatts (MW) per year, or approximately 6,500 households.

SRCSD also buys some of the steam produced by the recycled methane to heat the wastewater digesters at the Wastewater Treatment Plant. In the event of a local power failure, the cogeneration plant serves as a backup power supply to keep the treatment plant running.

Estimated annual emissions reductions from the methane recycling program:

The primary GHG reduction (for Methane) is 96% - from 10.76 tons/year to 0.454 tons/year.

Natural Gas Versus Coal

The Carson Ice-Gen Project uses both natural gas and digester gas to make electricity, which results in an overall emissions reduction which benefits the customers of SRCSD and SMUD, whose two service areas overlap. A lower amount of air pollutants and greenhouse gases are emitted when natural gas is used to produce energy, when compared to burning coal. Typical values for pounds of emissions per billion BTUs of energy produced are:

Source: EIA Natural Gas and Trends 1998

To learn more about natural gas visit http://www.naturalgas.org/environment/naturalgas.asp

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