Burning Takes Bite Out of Landfill Gas

Although planes, trains and automobiles are responsible for the lion's share of global greenhouse gas emissions, sources such as industrial plants and landfill sites are also major contributors. Understanding more about emissions from these stationary sources — and the effectiveness of technologies being used to control them — assists in designing preventative and control measures to reduce their impacts on air quality and climate change.

Environment Canada's Environmental Technology Centre (ETC) is determining how these sources stack up by collecting, analyzing and monitoring emissions at sites across Canada. Among the assessments currently under way is one on the combustion of landfill gas — a mixture of gases produced by the decomposition of degradable organic material in landfill sites. The ETC's efforts have determined that several of these methods are effective ways of destroying many harmful components of landfill gas, and reducing its impact on climate change.

Landfill gas is composed primarily of methane and carbon dioxide, but can contain trace amounts of hundreds of other compounds, with the exact composition varying from site to site. Carbon dioxide is the greenhouse gas most commonly associated with climate change, and the most prevalent of those emitted as a result of human activity. However, methane is a much more powerful greenhouse gas — with a warming effect 21 times that of carbon dioxide. Since one quarter of all the methane produced by human activity is from landfill, limiting emissions from this source is one of the strategies encouraged by the Kyoto Protocol on Climate Change.

Burning landfill gas converts methane into carbon dioxide, and therefore dramatically reduces its impact on climate change. If even half of all the landfill gas produced in Canada were combusted, it would mean a reduction equivalent to some six million tonnes of carbon dioxide annually. There are a number of landfill sites across the country where landfill gas is collected and burned in flares — either in the open air or in more efficient enclosed stacks. At a growing number, however, landfill gas is burned in boilers or industrial-scale internal combustion engines to produce energy. These methods have the added benefit of offsetting the consumption of other pollution-producing fossil fuels.

Although traditional methods of burning landfill gas destroy many of its harmful components, some compounds may still be released into the air — including volatile organic compounds (VOCs), which are precursors of smog, ozone-depleting substances such as freons, and toxic substances such as vinyl chloride and 1,3-butadiene. Others may be created through the combustion process or as the result of incomplete combustion, including carbon monoxide, sulphur and nitrogen oxides, dioxins and furans, and polycyclic aromatic hydrocarbons.

In order to reduce the potential impacts of these emissions on human and environmental health, Environment Canada is evaluating the effectiveness of several technologies used to burn landfill gas. Emissions studies have been carried out at the Meloche landfill in Montréal and in Waterloo, Ontario, on reciprocating engines that burn landfill gas to generate electrical energy that is then fed into electricity distribution grids. Additional studies have looked at emissions from a boiler in suburban Toronto, and an enclosed flare in Ottawa.

More studies are already being considered, but results to date show that boilers and enclosed flares can destroy over 99 per cent of the amount of the compounds present in the landfill gas, while reciprocating engines can destroy about 95 per cent. Engineers have found that these processes also produce relatively low levels of other gases such as carbon monoxide, hydrogen sulphide and halogenated hydrocarbons.

These results present a compelling argument for capturing landfill gas and turning it into “green power”. The further development of this kind of power generation will require commitments from municipalities and private landfill operators to invest in existing and new technologies, while incentives will also be required to promote the recovery and use of landfill gas across Canada.

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