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Printable Landfill Gas Factsheet (Updated Nov 2007)
Landfill Gas Powerpoint Presentation (June 2012)
Primer on Landfill Gas as Green Energy
By Mike Ewall
"Landfill gas" is not the same thing as "natural gas" or "methane." They are three separate terms which mean different things. They should not be used interchangeably. The term "landfill methane" is deceiving as it's usually used to imply that landfill gas is simply methane.
Methane is a hydrocarbon gas (CH4). It is a greenhouse gas and it is explosive. It is generated by decomposition (in landfills, from swamps, in the stomachs of cows, etc.).
Natural gas is approximately 80-99% methane, with the remainder being mostly other hydrocarbons (ethane, propane, butane, etc.) as well as some nitrogen, oxygen, water, CO2, sulfur and various contaminants.1
Landfill gas is about 40-60% methane, with the remainder being mostly carbon dioxide (CO2). Landfill gas also contains varying amounts of nitrogen, oxygen, water vapor, sulfur and a hundreds of other contaminants -- most of which are known as "non-methane organic compounds" or NMOCs. Inorganic contaminants like mercury are also known to be present in landfill gas. Sometimes, even radioactive contaminants such as tritium (radioactive hydrogen) have been found in landfill gas.
NMOCs usually make up less than 1% of landfill gas. EPA identifies 94 NMOCs in their 1991 report, "Air Emissions from Municipal Solid Waste Landfills - Background Information for Proposed Standards and Guidelines." Many of these are toxic chemicals like benzene, toluene, chloroform, vinyl chloride, carbon tetrachloride, and 1,1,1 trichloroethane. At least 41 of these are halogenated compounds. Many others are non-halogenated toxic chemicals. 2, 3 More exhaustive test for contaminants in landfill gas have found hundreds of different NMOC contaminants.
When halogenated chemicals (chemicals containing halogens - typically chlorine, fluorine, or bromine) are combusted in the presence of hydrocarbons, they can recombine into highly toxic compounds such as dioxins and furans, the most toxic chemicals ever studied. Burning at high temperatures doesn't solve the problem as dioxins are formed at low temperatures and can be formed as the gases are cooling down after the combustion process.4
Matter cannot be created or destroyed - it is one of the first lessons of high school physics. Throughout EPA's reports on landfill gas utilization, they refer to the destruction efficiency of various landfill gas combustion technologies. They usually assume it's about 98% or more. In other words, they pretend that these halogenated non-methane organic compounds simply go away. There is almost no talk about what happens to the chlorine, fluorine and bromine atoms that go into the burner.
Mercury and tritium cannot be destroyed through combustion and no efforts have been made to prevent their release into the environment when landfill gas is collected and burned.
Landfills Make Mercury More Toxic
There is limited data comparing emissions from landfill gas flares to energy producing combustion devices (which includes boilers, turbines and internal combustion engines).
According to very limited data in a 1995 EPA report, carbon monoxide and NOx emissions are highest from internal combustion engines and lowest from boilers. Flares and gas turbines are in the middle.5
Dioxin emissions data is also very sparse. EPA, in their 1998 dioxin inventory, looks at only a few tests and shows that, for the most part, flares produce more dioxin than internal combustion engines or boiler mufflers.6 However, a more comprehensive review (by the County Sanitation Districts of Los Angeles County in 1998) of about 20 studies involving 76 tests at 27 facilities shows that internal combustion engines on average produce 44% more dioxin than shrouded flares. Since there is high variability in dioxin emissions from landfill gas burners (based on composition of waste dumped and also on the combustion technology - internal combustion engines are much more variable), these figures should not be applied to site-specific situations.7
Burning landfill gas is dirtier than burning natural gas. Whether using an internal combustion engine or a gas turbine, burning landfill gas to produce energy emits more pollution per kilowatt hour than natural gas does.8
Why is it that natural gas (a non-renewable resource which is not considered "green energy") burns cleaner than landfill gas, yet energy from landfill gas gets away with being considered renewable green power?
This is a classic case of asking the wrong question.
It's a very different thing to ask "what is the best way to manage landfill gas?" than to ask "how should we produce green, renewable energy?"
Green energy marketers aren't in the business of managing landfill gas. If they want to be in the waste management business, then that's a different story.
In brief, if you ask what the best way to manage landfill gas is, the answer is along the lines of "before you do anything with it, filter out the toxic contaminants and treat them with a non-burn technology." If the question is how to produce green, renewable energy, the answer is "use technologies such as wind and solar that don't create pollution in the process of making energy."
Nothing that emits dioxins should be considered "green" or "renewable" energy.
"Green" or "renewable" resources shouldn't produce pollution in the process of making energy. Anything that has environmentally-damaging emissions you can measure per kilowatt is not deserving of subsidies or preferential pricing afforded to "green power."
Well, let's examine the options:
The default option is to do nothing. Doing nothing leads to gas migration off-site and can cause explosions. The release of the methane creates some global warming problems and the release of the toxic contaminants can cause cancer and other health problems in local communities. A New York study of 38 landfills found that women living near solid waste landfills where gas is escaping have a four-fold increased chance of bladder cancer or leukemia.9, 10
Landfills should install gas collection systems to prevent the problems with gas migration. Once collected, landfills can do any of the other options. These options are focused around handling the methane (usually by burning it) and are not focused around addressing the toxics issues. Regardless of what is ultimately done with the gas, the gas should be filtered so that the halogenated compounds are segregated. Once filtered out, these compounds should not be combusted (as that doesn't tend to improve the situation, but may make it worse). They should be handled as hazardous waste and isolated from the environment as best as is possible until there is a proven technology which can neutralize the toxics by converting the halogens to relatively harmless chemicals like salts.
The general options for dealing with landfill gas (once collected) are as follows:
Note: a more comprehensive list of options is online at http://www.eia.doe.gov/cneaf/solar.renewables/renewable.energy.annual/chap10.html
Flaring of landfill gas is either done in a candle flare or a shrouded flare. A candle flare is an open air flame. With such, there is no reliable means to monitor for dioxins or other toxic emissions. Shrouded flares involve enclosing the flame in an insulated cylindrical shroud which can be anywhere from 16 to 60 feet tall.11 While dioxins can be tested for in such flares, it is possible that enclosing the flare will keep the post-combustion temperature in dioxin-formation range, resulting in increased dioxin emissions. Essentially, this is a lose-lose situation. It should be noted that some (perhaps most or all) shrouded landfill gas flares have exit temperatures of around 1400oF - well above the dioxin formation range (which end around 752oF). In such cases, dioxins will be formed in mid-air as the exhaust hits the cooler background air after leaving the stack.
Boilers are among the cheapest options. They produce heat, not electricity. Boilers are generally less sensitive to landfill gas contaminants and therefore require less cleanup than other alternatives. Boilers have the lowest NOx and carbon monoxide emissions of the combustion technologies.12
Landfill gas use in boilers bring in the issue of piping the gas to local industries. While boilers themselves may not require much cleanup of the gas, the pipelines do require some cleanup, since corrosive compounds in the gas (particularly the acids and hydrogen sulfide - H2S) can damage the pipelines. There have been many concerns associated with landfill gas pipelines brought out by environmentalists living near landfills considering this use. Among the concerns are the integrity of the pipeline (at least one proposal involves lateral seams), liability issues, and the economic support of neighboring polluting industries which might use the gas.13 In addition, such projects have been used as excuses to develop additional polluting industry that would utilize the gas in their processes.
Internal Combustion Engines
IC engines are the dirtiest technology for burning landfill gas. They emit the most carbon monoxide and NOx and they may be the largest dioxin source of the available technologies.14
Gas turbines are somewhere in the middle in terms of carbon monoxide and NOx emissions. There isn't enough data on dioxin emissions from landfill gas turbines to provide any sort of comparison.
Fuel cells are the most expensive technology, as they are still largely experimental. EPA describes fuel cells as "potentially one of the cleanest energy conversion technologies available." In order not to "poison" the fuel cells, halogenated contaminants must be filtered out. This is a wonderful thing, since it demonstrates that such filtering technologies are realistic and may eventually be put into practice. However, in EPA's twisted logic, they state that the filtered contaminants would be incinerated.15 This would defeat the point of filtering them in the first place, unless all we care about is the health of fuel cells.
Conversion to Methanol and/or Dry Ice
At least one company is involved with converting methane from landfills into methyl alcohol or methanol. However, the halogenated organics they filter out are sent to a flare (again defeating the point).16 Other companies have expressed interest in converting the carbon dioxide in landfill gas to dry ice for sale to industry. They have claimed that the carbon dioxide in landfill gas is actually more profitable to recover than the methane.
Cleaning up the Gas to Pipeline Quality
Since natural gas prices are so low, this is not expected to be economical anytime soon. It also requires a high degree of cleaning and filtering the gas. To the extent that the gas is not adequately filtered, then the landfill gas will be degrading the quality of the natural gas by adding more contaminants to the system.17
As with any waste issue, the proactive solution is to look upstream and see what can be done to stop creating waste products. With landfill gas, it's no different. Landfills are the end-point of much of the excesses of our wasteful economy. At the very beginning of the system, we must look at such things as phasing out of halogens in industrial use. This is the only way that we can stop chlorine, fluorine and bromine pollution and the organohalogens (dioxins, furans, etc.) that come with them. We also must consider the technology of landfills. There are communities in the United States which are recycling 80-90% of their waste (some even higher). It is the act of mixing materials together that makes waste. Source separation and recycling prevents this.
In landfills themselves, it makes sense to segregate organic wastes from other wastes by placing them in different cells of a landfill. This would concentrate the methane generation in an area where many of the toxic compounds won't be present (which is not to imply that yard waste and such doesn't come laden with pesticides and toxic sludge "fertilizer" applications).18 In consideration of landfill gas management, EPA dismissed comments which would favor waste segregation.19
Promoters of landfill gas combustion consistently point to the fact that methane is a potent greenhouse gas. This gets used as a reason to burn landfill gas to produce energy and also to have that energy considered "green." Often ignored is the fact that most landfills which have gas collection systems are burning that gas in one form or another anyway. "Green energy" should not be used as an excuse to move from flares to internal combustion engines or gas turbines, as there is not a solid environmental argument for doing so. The incentives involved in green energy marketing are not enough that landfills without gas collection systems are going to install them to produce "renewable" energy from landfill gas. Landfill gas management should be based on isolation of toxic contaminants and not on the politics of global warming.
Proponents of landfill gas pipelines to boilers of local industries often argue that there would be displacement of other greenhouse-gas emitting fuels in the boilers of the pre-existing industries by the landfill gas that would be used in its place. While this can be a legitimate argument, it does not necessitate piping gas that is not cleaned up to natural gas pipeline standards.
EPA has a misnamed "Landfill Methane Outreach Program" which promotes burning landfill gas to produce energy. This program is part of EPA's Methane Outreach Programs which are a part of their Atmospheric Pollution Prevention Division.20 It is apparent that EPA's agenda on landfill gas management is being driven by global warming politics and not sound management of toxic air pollutants.
As greenhouse gases go, methane is the least potent next to carbon dioxide. According to the EPA, methane is 21 times more efficient at trapping heat than carbon dioxide (CO2). Nitrous oxide (N2O) is 310 times more efficient than CO2. Perfluorocarbons (PFCs) and hydrofluorocarbons (HFCs) are anywhere from around 1,000 to 10,000 times more effective than CO2. Another fluoridated compound, sulfur hexafluoride (SF6), traps 23,900 times as much heat as CO2.21 Methane is responsible for 10.6% of global warming damage from human-sources in the U.S. Of this, 35.8% is from landfill gas. Thus, 3.8% of U.S. global warming damage is from methane in landfill gas.22 This is hardly a reason to advocate burning it one way vs. another, or even burning it at all. Since methane in captured landfill gas can be converted to methyl alcohol without requiring combustion, there is no need to have to subject the other chemical contaminants in landfill gas to incineration.
Landfill gas and other "biomass" (incineration) technologies are cheaper to develop than wind (which is the next cheapest "renewable" technology). Energy from landfill gas projects also provides the easiest-to-obtain new renewable (built since the inception of green energy marketing) for the Green-e certification process.
It is because of this that we don't expect to see as much development of truly clean renewables from green energy marketing as we expect to see development of polluting landfill gas and biomass technologies. While not a renewable energy source, cheap natural gas is also likely to undercut renewables. Until we succeed at knocking out polluting technologies like "biomass" from the definition of renewables, we won't see the true potential for long overdue wind development.