From: VIT
Published December 7, 2007 08:46 AM

Combustion of waste may reduce greenhouse gas emissions

A joint research project of VTT and Finnish Environment Institute (SYKE) has proved that development of waste management is a cost-efficient means to reduce the emissions of greenhouse gases. Considerable reductions can be achieved by combustion of waste and by collecting methane from landfills. The collected methane can either be used directly in energy production or flared off, i.e. eliminated through combustion without energy production.

Landfills are significant sources of greenhouse gas emissions, mostly because of methane. Compared with carbon dioxide, methane is a twenty times stronger greenhouse gas, and landfills originate 4 % of the anthropogenic emissions. To reduce the emissions, the greenhouse gases generated in landfills should be collected, and biodegradable waste should be treated by other methods than landfilling.

According to the results of the study, treatment methods for biodegrad-able waste – composting and digestion – reduce the greenhouse gas emissions compared with landfilling. Biogas production in a digestion plant yields more emission reductions than composting, if the biogas can be utilized for production of heat, electricity, or traffic fuel. The efficiency is even better if the separation of waste components takes place already at the source and if fossile fuels are replaced by biogas.


More research on recycled material needed

According to the results of the project, the use of recycled material does not always reduce the greenhouse gas emissions. This result is based on a comparative life cycle analysis of products made of recycled and virgin materials, respectively. Emission reductions are usually obtained when recycled materials replace fossile fuels. If the replaced material is of biotic origin, it is not always possible to obtain reductions. Even other factors, such as the treatment of the waste material and the fate of the products after the use, affect the emission balance.

In the case studies, the recycled plastic profile was a construction material made of plastic waste, and it was compared with board made of impregnated wood. An oil-absorbing sheet made of recycled textile was compared with oil-repellent products made of virgin polypropylene fibre. In all comparisons, the recycling of textiles led to emission reductions compared with the use of virgin plastic.

The use of recycled plastic as raw material for construction material was founbd to be better than the use of impregnated wood only in case the combustion of plastic was avoided. If the replaced material had been fossile-based, or concrete, or steel, the result would probably have been more favourable to the recycling of plastic. More research on the emission balances of recycling would give us more accurate information on the benefits of recycling processes.

Changes in waste management

The waste management branch is undergoing a period of changes. Landfilling will be reduced and new methods to use the waste are developed. The EU has set the goal to cover 20 % of the energy demand by renewable energy sources by 2020. By using the energy content of waste it is possible to reduce greenhouse gas emissions, as the energy produced by the combustion of wastes can replace energy produced by using other fuels.Waste management systems are complex, and it is not possible to give universally valid instructions for cost-efficient reduction of greenhouse gas emissions. In local waste management development plans, each of the alternative measures should be assessed considering the local conditions. When the decision is made, not only greenhouse gases but all environmental effects should be regarded.

Results were used by the IPCC

The joint research project of VTT and SYKE compared the greenhouse gas reduction efficiencies and the cost efficiencies of various waste management concepts. The project was a part of the Climbus Technology Programme of Tekes, and it was funded by Tekes, YTV (Association of the municipalities of the Helsinki region), Kuusakoski Oy, and Vapo Oy. Some of the results of the project have been used in the assessment report of the Nobel price awarded Intergovernmental Panel on Climate Change (IPCC).


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