Landfill Gas Monitoring

Landfill gas (LFG) is generated during the normal bacterial decomposition of organic material contained in municipal solid waste (MSW) landfills. It is comprised primarily of methane and carbon dioxide, with small amounts of other constituents such as N2, O2, H2, H2S and VOCs.

ALS - Columbia offers a wide variety of tests for the characterization of landfill gas for applications such as routine monitoring, Tier II compliance and gas-to-energy projects.

By volume, LFG is typically 30-60% methane and 30-40% carbon dioxide and water vapor. Oxygen is usually present at concentrations between 1-5%. Nonmethane organic compounds (NMOCs) are generally present between 2,000 to 10,000 ppmV, and hydrogen sulfide ranges from 10 to 500 ppmV.

The balance of the gas consists of small amounts of nitrogen, hydrogen and trace amounts of inorganic compounds. NMOCs include certain hazardous air pollutants (HAPs) and volatile organic compounds (VOCs), which can react with sunlight to form ground–level ozone (smog) if uncontrolled. Nearly 30 organic HAPs have been identified in uncontrolled LFG, including benzene, toluene, ethyl benzene, and vinyl chloride. Some of the constituents of LFG have strong, pungent odors, such as hydrogen sulfide.

LFG can be used as a source of energy to create electricity or heat. It is classified as a medium-Btu gas with a heating value of 350 to 600 Btu per cubic foot, approximately half that of natural gas. LFG can be used in place of conventional fossil fuels in certain applications. By using LFG to produce energy, landfills can significantly reduce their emissions of methane and avoid the need to generate energy from fossil fuels, thus reducing emissions of carbon dioxide, sulfur dioxide, nitrogen oxides, and other pollutants from fossil fuel combustion.

Due to the increased use of disposable personal hygiene products and polymer-based containers, landfill operations have developed an increased awareness of “unregulated” compounds, such as siloxanes. While siloxanes are not currently considered to pose risks to human health, they do create very real mechanical impacts on the equipment.

During combustion, all silicon-containing compounds (siloxanes) react to form silicon dioxide, which results in the formation of deposits on the internal components of combustion engines. These deposits can greatly impede the performance efficiency of the power-generating turbines, thus it is desirable that the siloxanes be removed from the gas by either chemical or mechanical means.

The following is a list of common siloxanes, also referred to as volatile organic silicon compounds (VOSCs):

D₃, D₄, D₅, L₂, L₃ and TMS are the siloxanes most commonly detected in landfill gas.

ALS - Columbia has developed a novel sampling and analytical approach for siloxanes. It involves collecting landfill gas with a sorbent tube, followed by extraction at the laboratory and analysis by gas chromatography/mass spectrometry.

Benefits of this new approach:

• Sampling is relatively simple. It does not require ice baths or complicated setups. Depending on the configuration of the sampling location, it can be as simple as connecting a length of tubing to a sampling port, connecting a rotameter to moderate the flow rate, and attaching the sample tube. After approximately 30 minutes, the sampling is completed, and the tubes may be disconnected and submitted to the lab for analysis.
• Since the samples are collected on tubes rather than with impingers of methanol solutions or in bags with flammable landfill gas, they do not represent a Dangerous Good or Hazardous Material. Therefore, they can be shipped more cost-effectively using normal shipping procedures. They do not require special boxes, containers, labels, documentation or additional procedures.
• The data is reported in several units: µg/Tube, µg/m³, and as µg/m³ as Silicon, to accommodate a variety of uses or calculations by the end user.

ALS - Columbia supports the following methods often used to characterize landfill gas:

• Methane by EPA Method 3C modified or EPA Method 25C modified
• Carbon Dioxide by EPA 3C modified
• Hydrogen, Oxygen, Nitrogen, Carbon Monoxide by EPA 3C modified
• TNMOC by EPA 25C modified
• BTU analysis by ASTM D3588
• Hydrogen Sulfide and reduced sulfur compounds by ASTM D5504
• VOCs by EPA TO-15
• Siloxanes by CAS in-house method

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