Landfill gas is often mistaken for being a single type of gas due to being referred to by the LFG term. Yet, it’s actually a combination of hundreds of different gases. Each day’s gas production can vary slightly, making it tricky to exactly track the composition and energy value of the supply. Most power and heating projects that rely on LFG use processing equipment to separate the gases out, resulting in a relatively steady supply during certain periods of production. Mixed gases harvested during certain periods of the landfill’s aging process are pure enough to use with little to no additional processing. Explore the main components of mixed LFG and how they change in volume over time to get a better understanding of what needs control and containment at a capped landfill site.
Methane
The most valuable gas produced by the municipal solid waste landfill is methane. It makes up approximately half of the LFG by volume, although this varies greatly during the different phases of decomposition. Methane comes primarily from the breakdown of organic material, so landfills with greater volumes of yard waste, food scraps, and other materials will produce more methane. However, carbon dioxide production also goes up in scale with the methane production, so the gas mix will remain close to half and half for both regardless. Only processing can change the percentage of methane in the final gas product and increase methane concentration to make it more valuable as a heat and power source.
Carbon Dioxide
Burning LFG with carbon dioxide mixed in produces a lower ratio of fuel to power, but it results in the destruction of carbon dioxide with minimal release into the air. Nearly half of all LFG over the course of a landfill’s lifespan will be carbon dioxide, with the first phase of gas production consisting almost entirely of CO2 and nitrogen gas. Separating methane from carbon dioxide is a common processing step for fuel production, but that leaves the CO2 behind and in need of disposal. Incineration works well, but it requires energy rather than producing it. Other uses for concentrated CO2 gas include delivering it to nearby greenhouses to increase the growth rate and fruiting of the plants inside.
Nitrogen
Making up nearly 80% of LFG in the first few months of decomposition and then falling to a mere 5% of total volume the rest of the time, the nitrogen from a landfill is volatile and hard to use. It’s also a common cause of bacterial and plant growth issues if allowed to escape since it’s a potent fertilizer. Since the volume of this gas is relatively low during most stages of LFG production, it’s generally processed out of purified methane to keep it from interfering with power or heating uses. Nitrogen is often condensed along with ammonia gases in a leachate system for eventual reuse as a plant fertilizer or soil conditioner.
Ammonia
One of the most potent odor issues from landfill gas comes from ammonia. Although it only accounts for 1% or less of the total volume of the LFG, it’s easily detected in low concentrations by the human nose. It’s also a potent irritant and can damage metal equipment and piping through the acceleration of corrosion. It’s essential for gas control systems to be built to resist the most volatile gases like ammonia. If this gas is separated out from the methane to improve its fuel value, it’s usually converted into fertilizer or released into greenhouse environments to stimulate growth and for pest control.
Trace Gases
The rest of any LFG supply is made up of trace gases that usually come from the volatilization of chemicals mixed into the municipal waste supply. These gases can include various sulfides, organic compounds like benzene, and small amounts of hydrogen. While each of these gases can have various industrial and chemical uses elsewhere, the volumes are usually so low they’re not worth harvesting separately. These gases are generally burned up as raw LFG is combusted for power generation or extracted during processing and disposed of in another form.
When you consider the varying percentage of oxygen, you can see why LFG is a complex product to collect and use. Make the best possible use of the methane and other gases with impermeable covers that allow for pressurization of the entire system. BTL Liners has the cover and liner products that are durable enough to last for decades, even in the challenging environment of a modern sanitary landfill cell.
