Energy recovery from municipal waste technologies
A recent study has explored the impact of greenhouse gas (GHG) emissions from different technologies used to treat municipal solid waste for energy recovery.
Municipal Solid Waste (MSW) consists mainly of household and some commercial and industrial waste, collected by a local authority. On average in the EU, almost 19 per cent of MSW is treated for the recovery of energy, but figures vary widely. For example, in 2006, 54 per cent and 46 per cent of MSW was treated in Energy from Waste (EfW) plants in Denmark and Sweden respectively. This compares with only 11 per cent in England.
Using England as a case study, the researchers modelled emissions of three main greenhouse gases (GHGs): carbon dioxide, methane and nitrous oxide, released by waste management. They also considered GHG emissions saved through recovering energy from waste and recycling of materials. Significant amounts of methane in particular are generated by landfill.
Three types of treatment options were examined.
- Mass Burn Incineration (MBI). This is the combustion of large volumes of MSW in a single-stage chamber. Usually energy is recovered from electricity generated by high temperature steam turbines.
- Mechanical Biological Treatment (MBT). This involves mechanical sorting of some parts of the waste for recycling and biological treatment of other parts. There are many different products of MBT, including metals, compost, stabilised waste for landfill and Solid Recovered Fuel.
- Mechanical Heat Treatment (MHT). This uses a relatively new technology in which steam pre-treats the waste to break it down into its organic and inorganic components before it is separated into fractions including secondary recycling (e.g. metals) and cellulose fibre (which could be used for Solid Recovered Fuel or compost).
Results from the study suggest that overall GHG emissions are greatly affected by how the Solid Recovered Fuel is treated and used. MHT provides the greatest GHG savings provided there is an end market for the fuel. As the fuel produced using MHT contains substantial amounts of biodegradable waste, it could release significant amounts of methane if placed in landfill. If a Solid Recovered Fuel market does not exist, further biological treatment would be necessary to reduce the amount of biodegradable material.
Recycling significantly reduces GHG emissions. However, if demand for recyclables is low, savings of GHGs can still be made by all options except MBI (in cases where no energy is recovered) and MBI if energy is recovered through electricity generation.
If 25 per cent of MSW is treated in EfW plants in 2020, England could make GHG emissions savings ranging from 1.12-2 million tonnes of CO2 equivalents (global warming potential of an equivalent amount of carbon dioxide), depending on the technologies used and the state of the recycling market.
Source: Papageorgiou, A., Barton, J.R., Karagiannidis, A. (2009). Assessment of the greenhouse effect impact of technologies used for energy recovery from municipal waste: A case for England. Journal of Environmental Management. 90:2999-3012.