Global Warming, Greenhouse Gases and Waste Disposal/Incineration
By Brian Latham, Enviros Associate.
(The views expressed do not necessarily reflect those held by Enviros or the Landfill Gas Team.)
Let us begin with a fact. There is abundant evidence from geology, archaeology, history and meteorology, that climate changes from time to time and there is abundant evidence that changes can be rapid and extreme. For example about 100,000 years ago the climate of British Isles, like the rest of Europe as far south as the Alps, changed from sub-tropical to arctic in the space of a few hundred years.
There are many such instances and yet there seems to be a presumption that climate change is a new phenomenon brought about solely by modern man's abuse of the environment.
Intergovernmental Panel on Climate Change
Human activity is not the primary cause of climate change although it might well affect the way that changes occur. This was recognised by the Intergovernmental Panel on Climate Change (IPCC) when, in 1996, it reported "the balance of evidence suggests a discernible human influence on the climate".
Read this carefully and note the level of uncertainty. "Balance of evidence", "suggests", "discernible" and even "influence" are a long way from a categorical statement that human activity is causing an otherwise stable climate to change. Yet there seems to be a widespread belief that this is what the report said.
Published at a different time, the IPCC report might have disappeared into obscurity. Instead it struck a chord with politicians and public alike and continues to have a profound influence on the western way of life at the start of the 21st Century. Politicians throughout Europe and some in the United States, are promoting policies intended to reduce energy consumption and produce less waste. They enjoy a level of public support that they probably never imagined, all in the name of preventing climate change. How so? Because irrespective of abundant evidence of past climate change and the uncertainties in the findings of IPCC, the public at large has a gut feeling that it cannot be beneficial to push all of this stuff into the atmosphere and the climate must be changing because it is too hot, too wet, too windy etc. Cause and effect are never questioned.
Fascinating though they are, the causes of climate change are academic to the waste manager who has to deal with the practical consequences of political policies. At the Kyoto Summit, the UK Government pledged to reduce the emission of greenhouse gases into the atmosphere and waste management is one of the key sectors involved. One of the key elements of the Government's and Europe's strategy to reduce greenhouse gas emissions is to shift the disposal of biodegradable waste away from landfill to other systems, particularly composting and incineration. The objective is simple, to reduce the amount of methane (a greenhouse gas about 21 times more powerful than carbon dioxide) produced as landfill gas and released into the atmosphere. This objective is fundamental to the EU Landfill Directive.
Would that it were so simple!
Greenhouse Gas Generation - Landfilling and Incineration Compared
When waste is incinerated, two greenhouse gases are produced, carbon dioxide and nitrous oxide. The IPCC has produced detailed guidance on what counts as greenhouse gas and what does not. Applying these rules to incinerator emissions, only the carbon dioxide produced from combustion of fossil (non biogenic) carbon (eg plastic) counts as greenhouse gas. That from biogenic material (paper, wood etc) does not count because its carbon is part of the natural carbon cycle. If the incinerator utilises the combustion heat then the energy produced substitutes for energy generated from fossil fuel. The net greenhouse gas emissions from the incinerator are calculated by subtracting the emissions avoided from the gross emissions.
When similar waste is landfilled, only one greenhouse gas is produced, methane. All of the methane is counted as greenhouse gas because methane is not part of the carbon cycle. The carbon dioxide in landfill gas is produced by anaerobic digestion from biogenic carbon and so it is counted as greenhouse gas. If the methane is flared it is converted to carbon dioxide which again does not count as greenhouse gas because it is biogenic in origin. Furthermore if the methane is utilised as an energy source the energy produced substitutes for fossil fuel derived energy and the avoided emissions can therefore be subtracted from the gross landfill emissions. Landfilling has one other surprise in store. Some of the organic matter degrades so slowly that it is classed as stored or sequestered. This can also be counted as avoided emission and deducted from the gross emissions.
All of this sounds like comparing apples with oranges. How can the real greenhouse gas impacts of different gases be compared and how can the avoided emissions be quantified?
And then, if we are to compare the merits of alternative waste management schemes, how are we to take into account the greenhouse gas emissions from waste collection, haulage etc?
In fact, IPCC recommends a fairly straight forward methodology whereby different greenhouse gases can be compared by using carbon dioxide as a datum for comparison. By definition 1 kilogram of carbon dioxide has a Global Warming Potential (GWP) of 1. Methane has a GWP of 21 so 1 kg of methane has the same heat trapping potential as 21 kg of carbon dioxide.
To enable simple direct comparisons to be made between different gases and different scenarios, it is helpful to convert emissions to their Total Carbon Equivalents. Carbon dioxide is 12/44 (0.27) carbon. The TCE of any greenhouse gas can be calculated simply by multiplying its GWP by 0.27. So 1 tonne of carbon dioxide is equal to 0.27 tonnes Total Carbon Equivalent (TCE) and 1 tonne of methane is equivalent to 21 x 0.75 or 15.8 TCE.
If we assume that after decomposition, in the long term, all the carbon in the waste sent to landfill will be converted to carbon gas, as it will, we assume do so in the short term, during incineration, the relative carbon tonnages are equal.
However, the impact of even a small methane emission, (even if most methane gas is flared and becomes carbon dioxide), is so much greater than the TCE for the equivalent carbon dioxide produced, that the incineration option has to be considered.
The results of comparing incineration of a unit tonnage of typical household waste with landfilling the same tonnage - assuming collection, haulage and the other externalities are brodly similar in both cases - are surprising because they depart significantly from the "landfill bad - incinerator good" dogma with which we have become so familiar. The fact is that we should be quite clear that if incineration is to be rejected as a main-stream residual waste treatment option in the UK, the reasons for doing so will clearly lie elsewhere.
In a recent US study, the landfill with methane extraction and electricity generation comes out slightly better than the incinerator, but the differences are so small that the externalities such as emissions from haulage can make all the difference.
Conclusion
Global warming (Climate Change) may or may not be a reality.
By applying the IPCC protocol, it becomes clear that there is not much to choose between the net greenhouse gas emissions of an incinerator with energy recovery and a landfill with landfill gas utilisation.
The reasons for public rejection of incineration may be many, but should not be based on global warming issues in this instance.
|
