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From Garbage to Gas to Energy

Landfill Gas to Energy (LFGTE) isn't likely to win any beauty prizes in the renewable energy sweepstakes -- wind and solar continue to garner all the glamour. But this unsung method of harvesting landfill methane for conversion to electricity (or for direct use as a fuel for industry or vehicles) continues to prove that LFGTE is a scrappy long-term contender in the war on man-made greenhouse gases.

The technology is now fully mature.  Of some 2400 landfills in the U.S., more than 500 landfill gas conversion plants are operating today, with another 500 sites under consideration. 

“People have been commercially recovering landfill gas since 1975,” said Jean Bogner, a 2007 Nobel Peace Prize laureate and geochemist at the University of Illinois at Chicago.  “Compared to biomass, the good thing about municipal solid waste is there’s a good, established collection system for it.” 

Landfill methane gas is generated by decomposing organic material in municipal solid waste like food, yard waste, leaves, grass, paper, and lumber and accounts for about a quarter of total man-made U.S. methane emissions.  Even so, LFGTE projects still amount to only a fraction of a percent of the country’s total energy production.

“We’re starting to more and more view waste as a valuable product that we can either reuse or that has organic content that we can extract,” said Mikhail Chester, a civil engineer at Arizona State University.

The U.S.’ Clean Air Act dictates that at the very least, landfill owners capture gases and periodically flare them off to prevent dangerous buildup.  Beyond the landfill gas’ local volatility, due to methane’s heat trapping ability, this greenhouse gas warms the earth 23 times more than carbon dioxide. Thus, it only makes sense to use this landfill gas to either directly to run an industrial boiler or kiln, or run a turbine that can generate electricity.

Landfill gas is extracted using a series of wells, pipes and vacuums that collect upwards of 95 percent of an average landfill’s gas.  The gas is oxidized during the burning process to produce water and carbon dioxide, then used directly to replace fossil fuels in industrial and manufacturing operations, or cleaned of impurities so that it can be used in pipelines and vehicles.  But electricity from LFGTE still makes up about 70 percent of the U.S. projects that do more than just flare the gas.

Suburban Atlanta’s Seminole landfill in DeKalb County became Georgia Power’s first green project in 2006. Since 2010, the utility has also been buying electricity from Savannah’s Superior Landfill to energy project, set up by Houston-based Waste Management Inc. 

Georgia Power only pays the landfill operators what it would cost the utility to generate the equivalent amount of electricity.  Although combined both these plants have a total capacity of about 10 megawatts (MW) — a fraction of the utility’s total electrical capacity of almost 16,000 MW — Georgia Power spokesperson Lynn Wallace says the company is considering other such partnerships.

For its part, Waste Management is currently operating 131 such plants in the U.S. and Canada with 10 more now under construction or scheduled to break ground this year and another 30 in development.

“Our goal is to quadruple the amount of energy we produce from waste,” said Waste Management’s spokesperson Lynn Brown.  “We’ve upgraded our turbine technology in the last 5 years to make it more efficient.  But each landfill has its own characteristics.  Even climate can dictate how much gas you get out of a landfill.  In dry climates you don’t get much; if you get a lot of rain you might get more.”

Installation costs average $1.2 million to 1.8 million per megawatt with a typical urban project running between $5 and $10 million.

But to be effective, the smallest LFGTE project requires at least half a million tons of solid waste.  This isn’t an option for home recyclers or even fiercely independent large-scale ranchers. (For every one million tons of municipal solid waste that is collected, a 780-kW capacity electricity plant could be built.)

The EPA’s landfill methane outreach program notes that LFGTE projects generated more than more than 15 million megawatt-hours last year, with the biggest single U.S. project being the 50-MW Puente Hills landfill project. 

At the other end of the spectrum, in 2010, Green kW Energy installed a project on the site of a landfill closed in 2001 in Montgomery County, Virginia.  With an estimated 15 years of gas left to capture, electricity from its 265-kW generating system is being sold back on the grid.

“Green kW put up the capital and we just put in additional piping and meters,” said Alan Cummins, executive director of Montgomery Regional Solid Waste Authority in Christiansburg, Virginia.

As a result, Montgomery Regional Solid Waste Authority should soon start receiving about a $1000 a month, which they will put into a fund for a future local green energy education/training facility.

“More and more we’re seeing landfills outfitted with these systems,” said Chester.  “That tells me that the economics are working.  And it’s cost effective even when you have to go back and rip up the landfill to put it in.” 

In ranking how best to use the landfill gas once it’s extracted, Bogner puts direct use in existing gas-fired industrial boilers first.  Landfill gas methane also has the advantage of being more efficient than conventional natural gas, because it burns at a lower temperature. 

“If you have a factory or a sewage treatment plant next to a landfill site,” said Bogner, “you can run the gas right there without the expense of electrical generation equipment.” 

Conversion to electricity, she ranks second, followed by the third option of injecting the gas into pipelines or compressing or liquefying it for use in vehicles.  But Bogner says this third option is the most costly.  That’s because before use, the gas first has to be stripped of impurities, which for the moment, makes it the least attractive.

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