When organic waste ends up in a landfill, it will inevitably produce landfill gas (LFG is roughly 50% methane and 50% carbon dioxide). However, what happens to that gas varies greatly. Though most landfills have some gas collection infrastructure (functioning at various degrees of efficiency), nearly 80% of the time collected gas is simply be flared off. However, of approximately 2,400 landfills in the US, about 500 have some type of LFGTE (landfill gas-to-energy) system. This means that the landfill has a series of wells and pipes dug through it to capture the LFG and bring it to a power plant for conversion to energy. Estimates suggest that such systems can capture 60-90% of LFG. In 2011 it is estimated that these systems together produced more than 15 million kWh.
We visited one such gas-to-energy project at the Roosevelt Regional Landfill in Klickitat County, WA. Roosevelt, operated by Republic Services, was one of the first landfills in the US to capture LFG, and remains one of the largest projects of its type. The landfill receives ~2.5 million tons of waste per year from across the Northwest, and produces 21 megawatts of energy annually from this garbage at its onsite H.W. Hill Landfill Gas to Energy Project. The energy produced can power between 7,000 and 20,000 homes, depending on which estimate you read and the energy emitted at any one time. As the landfill grows, this capacity may also grow, and Republic Services estimates that future capacity may power as many as 30,000 homes.
The landfill includes a lechate recycling system, whereby lechate from the landfill is collected and poured back into the landfill. This is meant to speed up anaerobic decomposition, increasing gas output.
The EPA appears to be a major supporter of LFGTE projects as a source of ‘green energy’ and began its Landfill Methane Outreach Program (LMOP) in 1994. The EPA states that it “launched LMOP to encourage productive use of this resource as part of the United States’ commitment to reduce greenhouse gas emissions.”
But how do we define a ‘green’ or ‘renewable’ energy source? There is a major debate surrounding the classification of landfill gas-to-energy projects as ‘green.’ I’ll save this for a future post, but for now, consider a few things:
– To be effective, the smallest LFGTE project needs to receive at least half a million tons of MSW a year, which may result in an incentive to send organic materials to landfills. This may have something to do with the fact that there have recently been a number of cases in which Waste Management (the #1 waste company in the US) has worked to overturn several state bans on sending organics to the landfill.
– According to University of Washington professor Sally Brown, anaerobic digesters could capture significantly more gas from organics than landfill gas-to-energy systems, increasing the energy production potential significantly. So, if we are to take this energy source seriously as a ‘green’ energy alternative, do landfill capture systems make the most sense?
– LFGTE projects are said to ‘offset’ CO2 emissions. The Klickitat County Public Utility District writes that, over its 80 year lifespan, H.W. Hill will offset 35.4 million tons of CO2. But these figures are based on the CO2 that would be emitted from burning coal to produce the equivalent energy. These figures are a little bit misleading because they assume that the coal will be burned anyway.
Food for thought!