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Landfill Gas
Landfill gas is produced when microorganisms in a landfill break down biodegradable waste, such as food waste and paper. The gas is a mixture of methane and carbon dioxide, and the methane makes it a valuable fuel source. It is collected through a series of wells and pipes, constructed within the waste and is used to produce electricity, combined heat and power, or heat only.
Over the lifetime of a landfill, significant quantities of landfill gas are generated, e.g. a landfill accepting 100,000 tonnes of waste each year can generate as much as one MW of electricity on a continual basis. In 2006, 30% of renewable energy in the UK was generated from landfill gas. Over the last decade electricity generation from landfill gas has kept pace with the overall increase in renewable electricity generation, increasing nearly four-fold since 1998 to 4424Gwhr of generation in 2006, generation that otherwise would have been provided by burning fossil fuels.
Methane, the product of the breakdown of organic matter in the controlled environment of a landfill, must be tightly controlled. Historically the gas has been flared off to produce carbon dioxide, which has a much weaker greenhouse gas effect. Methane is around 21 times more potent than carbon dioxide and allowing methane escape to the atmosphere would have significant climate change implications. As the last decade has witnessed, increasingly landfill gas is being used to generate electricity or heat. Over the last decade, waste managers have reacted to a combination of the need to reduce greenhouse gas emissions whilst recovering higher value from the waste stream. As electricity generation from landfill has increased, emissions from the sites have fallen. Between 1990 and 2005 methane emissions from landfill fell by 61%.
ESA Members recognise the importance of effective landfill gas management. Modern landfills not only capture over 80% of methane generated, but incorporate high engineering standards to protect surface and groundwater, and manage gas production to the highest levels.
Landfilling of municipal waste has been in decline, decreasing from 79% in 2000/01 to an estimated 62% in 2005/6, responding to the Landfill Directive introduced in 1999 and landfill taxes introduced in 1996. The Government’s Waste Strategy 2007 was published last year providing a framework for the necessary investment in infrastructure to divert ever more waste from landfill to help Britain achieve its Landfill Directive targets and comply with EU waste law, EU driven targets specify that England must reduce the annual amount of Biological Municipal Waste landfilled to just 5.2m tonnes by 2020, less than half of current levels, with a move to higher levels of recycling and recovery. Defra predicts that the UK must invest £11b in new waste management capacity by 2020 to achieve this shift.
The movement away from landfill will, of course, have implications for the generation of renewable energy from landfill sites. The reduced biodegradable content of Municipal Solid Waste (MSW) being sent to landfill will reduce methane generation in landfill. However, given the lag in waste disposal, subsequent capping of the site, and the beginning and peak of gas production, significant volumes of landfill gas will still be produced for decades, though a long “tail” is anticipated which would be increasingly flared and electricity generation will fall.
Operators should be incentivised to continue to capture and generate energy from landfill gas. However the Government’s Energy Review in May 2007 actually reduced the incentive for operators to generate electricity from landfill gas by reducing economic support under the Renewables Obligation. Given the right economic incentives, much more energy could be recovered from waste – whether from landfill gas or other sources - using a range of technologies and offsetting carbon emissions from fossil fuel-sourced energy. The UK continues to recover much less energy from waste than other Member States and ESA has called consistently for all renewable energy from the biodegradable fraction of MSW to be supported by the Renewables Obligation, no matter what technology is applied.
Link: DTI Energy Statistics on Landfill
Landfill Leachate
During landfill site operation, a liquid known as 'leachate' is produced. This is a mixture of organic degradation products, liquid wastes and rainwater. Leachate is extremely variable in composition, depending on the nature of the waste in the landfill, the landfill design, etc., but typically has high organic carbon content, high concentrations of nitrogen, and is usually slightly acidic.
Landfills are designed and operated to seal the wastes as much as possible from the surrounding environment. Central to this environmental protection is avoiding groundwater
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