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One would be presumed crazy to throw cabbage into a dump, let it age and then collect it back on the assumption that is has become sauerkraut. But that is exactly what is done by indiscriminately throwing organic material into landfills and then attempting to collect the methane produced for Landfill Gas To Energy (LFGTE) projects.

The sauerkraut, LFGTE, can be made, but it must be done carefully or you will end up with rotten cabbage and increased greenhouse gas (GHG) impacts.

Plants capture carbon dioxide from the atmosphere to grow and then their ultimate decomposition releases the same carbon dioxide back into the atmosphere. This natural cycle is roughly (GHG) neutral.

But when the decomposition of plants occurs in an oxygen-deprived landfill, about half of the gas created is methane, which has a much greater GHG impact than carbon dioxide.

Many studies on methane’s GHF impacts use the Intergovernmental Panel on Climate Change (IPCC) figure of 25 times that of carbon dioxide measured at the IPCC standard 100 years. But methane decays in the atmosphere exponentially.

Thus the 100-year measure significantly understates the importance of reducing methane emissions in the short term. Over the next 20 years, methane has over 80 times the GHG impact of carbon dioxide, not 25.

Landfills are required to capture their methane, but to reduce the risk from explosion, not the risk from GHG impacts. Landfills are simply not planned, built, operated or capable of doing the needed GHG job.

The EPA’s estimated (and probably understated) 25% leakage rate acknowledges that methane migrates past even the best landfill methane collection equipment. Since landfill gas is about 50% methane with an 80x GHG impact at a 25% leakage rate, landfilling organics changes their natural GHG-neutral cycle into a GHG problem at least 10 times worse.

No amount of efficiency in converting landfill gas to energy can offset the GHG impacts from methane leaks.

The US needs to follow the lead of the EU that has since 1999 totally banned organics from landfills (even for use as alternative daily cover). We are in a deep GHG hole and we simply have to stop digging it deeper.

A ban on landfilling organics allows these resources to be diverted into digesters, composters, torrefiers, or other equipment that creates carbon neutral of negative outcomes.

Dr James Hansen of NASA suggests that the widespread pyrolysis of biomass may be critical to achieve the needed GHG reductions. Thus LFGTE projects should be initiated only to use the legacy landfill gas that remains after organics have been diverted.

And these legacy LFGTE project should utilize best technologies such as landfill covers that microbially oxidize fugitive methane. Legacy LFGTE projects must minimize methane leakage rather than maximizing methane usage.

That can be a high bar, given that LFGTE equipment is expensive and thus there exists an economic incentive to maximize methane output over the exact same short-term that methane leaks pack their most potent GHG punch.

It may be that new technologies, such as those for converting waste heat from landfill flares to energy, offer a more GHG-efficient method for monetizing landfill gas than the traditional LFGTE internal combustion generators.

But as we evaluate the GHG benefits of LFGTE projects, it’s not the fossil fuel displaced by methane that is in the landfill that counts most, but rather it’s the methane that is not in the landfill because organics are being diverted.

1. Global Warming: The Significance of Methane. Dessus, Laponche, LeTreut 2008
2. Target Atmospheric CO2: Where Should Humanity Aim? Hansen et 2008

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