The UK aims to produce 15% of its energy from renewable sources by 2020 (Department of Energy and Climate Change). One potential strategy towards meeting this target is to produce electricity by incinerating household waste, and there are already several plants in operation which do just this. The process has the added bonus of helping to meet stringent EU landfill targets by reducing the amount of household waste which is consigned to landfill sites.
What are the benefits of incineration?
Household waste incinerators with energy recovery have been operating in the UK since 1973. The waste is incinerated at a high temperature to convert it mainly to carbon dioxide, water and other gaseous substances. The flue gases are carefully treated to remove pollutants and then released into the atmosphere. The energy from this combustion is converted to electricity to supply the National Grid.
The incinerator bottom ash which remains after all combustible elements have been burned constitutes about 20-30% by mass of the original waste consignment (DEFRA 2007). Ferrous metals are removed from this ash to be recycled and the remainder can be used as an aggregate material principally for building roads.
Treatment of the flue gases involves injecting ammonia solution to convert nitrogen oxides to nitrogen gas and water, and the addition of lime milk to neutralise other acidic gases. Activated carbon is used to absorb any heavy metals or dioxins, and finally the gases are passed through a bag filter to remove any particulate waste (SELCHP Energy Recovery). The Air Pollution Control (APC) residue which results from these processes is classed as hazardous waste, and is therefore the only waste product which needs to be disposed of in landfill. It constitutes 2-6% of the original mass of the waste, thus representing a reduction in landfill mass of up to 98%.
The amount of energy generated from household waste incinerators is significant. For example, the Lakeside Energy from Waste plant at Colnbrook burns 410 000 tonnes of waste per year, generating 37MW of electricity: enough to power 50 000 homes, which is more than the population of Slough (Grundon Waste Management).
What are the potential environmental hazards?
New waste energy recovery plants inevitably meet with local opposition as they can be large, unsightly structures, and local residents worry about the environmental implications, in particular the risk of a reduction in air quality and the potential release of dioxins. The industry is therefore heavily regulated, and plants must comply with stringent standards set out in the Waste Incineration Directive.
There are two main areas for regulation set out in these directives. Firstly, the waste must be burned at a minimum combustion temperature for a minimum amount of time. This is to ensure the combustion of the waste is complete, and the minimum temperature also ensures toxic by-products of the combustion of plastics can be fully decomposed. Secondly, there are strict limits on the emission of a number of gaseous waste products to ensure air pollution is not significantly increased.
Clearly, there will be some increase in air pollution, however minimal, and carbon dioxide released from products manufactured from fossil fuels will also contribute to global warming. There will also be other local environmental issues such as the increase in traffic and associated pollution as trucks deliver the waste. However, these concerns need to be balanced against the need to significantly reduce waste going to landfill.
What are the future plans?
In 2001, the UK incinerated only 9% of its municipal solid waste (MSW). This is significantly less than a number of other countries including Denmark (52%) and the USA (15%) (DEFRA 2004). However, the figure has been rising, and in 2009 the amount of waste incinerated was 3.5 million tonnes, which represents 13% of the total waste produced (DEFRA website). In 2009, 12.7 million tonnes went to landfill, and this must be reduced to 10.1 million tonnes by 2020 in order to comply with the EU Landfill Directive.
New energy recovery plants are being planned and built in order to help increase the amount of waste incineration, thus reducing the need to use landfill. Two new facilities are currently under construction at Belvedere and Newhaven, and between them they will increase the capacity for waste incineration by nearly 700 000 tonnes. Both are due to come into commission in 2011.
A sustainable solution?
Energy recovery by waste incineration reduces the requirement to use landfill facilities, which improves sustainability. Waste products of the process are mostly recycled, but a small proportion (APC residue) has to be disposed of as hazardous waste. Waste incineration does produce polluting gases, although the emission of these is tightly regulated. Compared with generation of energy through burning fossil fuels, waste incineration is much more sustainable, especially when its favourable effects on waste management are taken into account.
DIRECTIVE 2000/76/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 4 December 2000 on the incineration of waste
“Incineration of Municipal Solid Waste” DEFRA 2007