Credit: Wisconsin Department of Natural Resources, CC BY-ND 2.0

Most of the garbage produced in America ends up in landfills, but there is something sweet in the foul smell: electricity generation. Landfill waste produces significant amounts of methane gas, which promotes the idea of collecting the potentially harmful emissions and converting it to electricity.

The Environmental Protection Agency considers landfill gas (LFG) energy generation to be environmentally friendly and a way to reduce reliance on fossil fuels. It has certain distinct advantages over wind and solar energy, as it’s not dependent on windy and sunny days, eliminating reliability issues during peak-use hours. It also is an economical alternative to other fuel sources, like natural gas.

Landfill gas, caused by the degradation of solid waste by anaerobic microorganisms, can be collected via different methods, a popular one of which is a series of wells drilled into a landfill and connected by a plastic piping system to an extraction site.

The gas in the system is processed and then used directly in reciprocating engines or further refined into a higher-BTU gas for such uses as powering boilers for manufacturing processes or electricity generation via gas turbines.

According to Treehugger.com, this multistep process includes compression, chilling, adsorption and membranes to remove impurities — such as sulfur, carbon dioxide, nitrogen and alcohols — from the gas stream. The purified stream is then fed into a natural gas liquefier, where it is cooled to below the natural gas boiling point of -260 degrees F to produce liquefied natural gas (LNG).

Once liquefaction takes place in an aluminum heat exchanger, refrigerants flow through one side while natural gas flows through the other side, cooling the natural gas into a liquid state so the LNG can be stored in a tank and delivered to filling stations.

In other words, after all the impurities, such as sulfur dioxide, are scrubbed out, you have pipeline-quality gas, which is high-enough quality to be blended with existing natural gas systems.

LFG that’s been processed and scrubbed is entirely suitable for electricity generation applications such as gas turbines and fuel cells, according to the California Energy Commission. It notes, “Southern California Edison and the Los Angeles Department of Water and Power operate a 40-kilowatt phosphoric acid fuel cell using processed landfill gas at a hotel/convention center complex in the City of Industry.”

And it’s been going on for a while; back in the mid-1990s, California already had 56 LFG recovery facilities, according to the CEC, which notes that “14 of them collected only gases and 42 others collected gases to produce electricity. These electricity facilities have an installed capacity of about 246 megawatts.”

So that’s some significant electricity production out of garbage.

And there is promise that LFG will be used to power homes, according to an announcement in late June by Waste Management of the construction of a gas-to-electricity facility at Geneva Landfill in Ashtabula County, Ohio. Scheduled for completion by the end of the year, the Waste Management Geneva Landfill’s gas plant is slated to generate 6.4 megawatts of electricity, which, according to WM officials, is enough to power over 6,000 homes.

Jerry Ross, senior district manager for Waste Management Geneva Landfill, notes that Waste Management is an experienced hand at this, as the company owns or operates over 130 LFG-to-energy facilities in North America — claimed to be more than any other company in the United States. All told, the company generates enough energy from LFG to power 1.1 million homes each year, and Ross says the company is looking to double that total by 2020.

Critics of LFG power generation point out that it’s not exactly “free,” however, since it does require considerable processing, and that it’s not a significant amount of energy produced. Of course, LFG energy is inherently kind of like a county gaining revenue by having inmates in the county prison buy their soft drinks from the commissary when incarcerating them is a net drain on society’s resources in the first place. Sure, it’s great that we can rake off some advantage from landfills by collecting the gas and converting it to usable energy, but, on balance, we’d be better off without landfills in the first place.

There’s also the question of the efficiency of current methane extraction methods. A recent study conducted by the University of Southampton in England noted that LFG collection is usually done by drilling vertical wells in the landfill, “but the effective length of the wells is limited to the depth of the unsaturated zone below the landfill cap. This often restricts the efficiency of such wells, and so several are required to cover a small area effectively.”

Vertical wells can also cause weakness in the cap, the university’s researchers found, as “air ingress can result in aerobic conditions in the landfill, perhaps causing fires and/or the development of explosive gas concentrations within the gas extraction infrastructure.”

There is also the expensive pipework required to connect the well to the extraction system, plus the fact that “vertical boreholes produce a large quantity of spoil when they are drilled,” according to the researchers. They said, “Disposal of spoil can be problematic, especially if it is contaminated.”

They looked into the advantages that horizontal collector wells might have in improving the efficiency of LFG extraction. They noted that such wells have been used in the past, “but, in most instances, the extraction wells have been installed as vent trenches in virgin ground beyond the periphery of the landfill site, or as gas drains within an operational landfill as filling progresses.”

In other words, these methods are “undesirable in closed landfills because the integrity of the engineered cap is compromised and a large volume of spoil is produced.”

That said, horizontal wells do have a larger zone of influence than vertical wells and therefore may increase gas yields or reduce the number of wells required, the researchers found, particularly at shallow sites, where “fewer wells will require less pipework and less balancing.”

The University of Southampton researchers also suggested that the disadvantages associated with conventional installation methods can be overcome by installing the horizontal collector wells via directional drilling technology, by, for example, “penetrating the landfill cap at the points of entry and exit only” and minimizing damage.

In 2006, Manufacturing.net reported that Montgomery, Ala.-based Jenkins Brick Co.’s manufacturing plant in Moody, Ala., was constructed as “the first major U.S. manufacturing facility” to use landfill gas as fuel, off information by the EPA. The $56 million plant sacrificed a bit of feng shui, being built adjacent to a landfill, but company officials told Manufacturing.net that LFG electricity would meet 40 percent of the plant’s energy needs and predicted it to meet 100 percent of needs within 10 years as the landfill grows.

Company officials said their usage of the methane would reduce greenhouse gas emissions by a carbon-dioxide-equivalent 62,000 metric tons per year.

“For centuries, bricks have been the building blocks of society, and now, by turning landfill waste into wealth, Jenkins Brick is also helping build a clean and plentiful energy supply for America,” said EPA Administrator Stephen L. Johnson. Manufacturing.net noted at the time that Veolia Environmental Services, the landfill owner “providing” the gas, and Jenkins Brick partnered with the EPA’s Landfill Methane Outreach Program to create the project. Jenkins Brick officials noted that since 1998, the company has been using clean-burning landfill gas to fuel the plant at its Montgomery headquarters.

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