Methane from Man Made Sources

Methane is a powerful greenhouse gas- 25 times more effective than carbon dioxide at trapping heat over a 100-year period. While it does occur naturally, major human-generated sources include landfills, refineries, oil and gas fields, natural gas infrastructure, dairies and wastewater treatment plants.

Concentrations of methane now exceed 1875 parts per billion, about 2.5 times as much as was in the atmosphere in the 1850s. Methane emissions come from diverse sources and sectors of the economy, unevenly dispersed across the landscape and not well tracked. Methane is also released from the natural biological process of enteric fermentation which is fermentation that takes place in the digestive systems of animals. In particular, ruminant animals that have two stomachs and eat grasses (cattle, buffalo, sheep, goats, and camels) produce and release methane from the microbial fermentation that breaks down the grass and hay into soluble products that can be utilized by the animal. Also, when natural gas and other petroleum products are used as a fuel incomplete combustion releases traces of methane.

“Atmospheric methane (CH4) is the second-most important greenhouse gas after carbon dioxide (CO2); the Intergovernmental Panel on Climate Change (IPCC) estimates that it was responsible for ∼about 20% of global anthropogenic direct radiative forcing from 2000 to 2010” begins a paper by Maryann R. Sargent et al-Majority of US urban natural gas emissions unaccounted for in inventories.

Globally wetlands contributed 30% of global methane emissions, with oil, gas, and coal activities accounting for 20%. Agriculture, including enteric fermentation (cow belching), manure management, and rice cultivation, made up 24% of emissions, and landfill gas contributed 11%. 

Landfill gas is generated during the natural process of bacterial decomposition of organic material contained in the trash buried in the landfill. Landfill gas is approximately forty to sixty percent methane, with the remainder being mostly carbon dioxide. Landfill gas also contains varying amounts of nitrogen, oxygen, water vapor, sulfur, and other contaminants.

The report highlights five areas where landfill methane emissions can be reduced:

• Preventing food waste from being generated along the entire supply chain
• Diverting organic waste from landfills by separating compostable waste. The limited success of recycling programs is a discouraging example of the potential for this solution.
• Rehabilitating old dump sites to install gas capture systems
• Changing landfill design and operation to enhance gas capture systems and minimize the release of methane
• Monitoring and quantifying emissions at landfills and composting facilities to pinpoint emissions sources and validate implemented abatement strategies

RMI, Carbon Mapper, and Integrated Global Greenhouse Gas Information System (IG3IS) released a report recently identifying the potential greenhouse gas reductions achievable through addressing methane emissions from municipal solid waste. Some of the flyover flights have identified landfills as point sources, not however Prince William County Landfill.

PW Landfill has operated for almost 40 years and has more than 7 million tons of trash buried at the landfill. That trash currently generates nearly 3,000 standard cubic feet per minute of landfill gas. In the late 1990’s NEO Prince William (Fortistar) installed a landfill gas collection system and a 1.9 Mega Watt generator tied into the electrical grid. This first stage of the renewable energy development program became operational in November 1998. The landfill electrical generation plant was expanded in November 2013. The facility, still operated by Fortistar, now generates a total of 6.7 MW of electricity. This is enough power for approximately 5,000 homes. NOVEC buys the renewable energy produced at the landfill and resells it to their customers.

Even with the expanded electrical generation there is still excess landfill gas available. So, the county built a pipeline from the landfill to the county animal shelter on Bristow Road with connections to several buildings along the way to provide landfill gas to heat the Fleet Maintenance Building and provide fuel to the Animal Shelter incinerator. A connection to the School bus garage was added in 2014 and other buildings are under consideration. This has allowed the County to replace propane with landfill gas which is a “Renewable Fuel Resource,” and reduce the energy footprint of our county.

  

For More Information read:

R B Jackson, M Saunois, P Bousquet , J G Canadell, B Poulter, A R Stavert , P Bergamaschi, Y Niwa , A Segers and A Tsuruta: Increasing anthropogenic methane emissions arise equally from agricultural and fossil fuel sources, Environ. Res. Lett. 15 (2020) 071002 https://iopscience.iop.org/article/10.1088/1748-9326/ab9ed2/pdf.