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Residues and Emissions
Burning waste produces certain residues and emissions. These are tightly controlled by the Environment Agency and most emissions have been reduced dramatically since 1990. Between 1990 and 1997 dioxin emissions from municipal waste incinerators fell by over 98 per cent and emissions of several heavy metals are now close to zero.
Residues
The main residues from incineration plants are incinerator bottom ash and air pollution control residues, approximately 25% and 3% by weight, respectively, of the incoming waste stream.
Incinerator bottom ash (IBA) from modern efw plants is an inert waste discharged from the end of the grate. The ash is cooled and is widely used throughout Europe as a secondary aggregate in road construction and the building industry. A report by the Environment Agency (July 2002) concluded that IBA is a valuable secondary aggregate and can be safely used in construction.
Air pollution control (APC) residues are generated when flue gases from the boiler pass through sophisticated multi-stage scrubbing systems for acid gas removal and a high efficiency filtration system. These residues are hazardous and must be safely disposed of in licensed engineered landfill site under very strict regulatory conditions.
Emissions
Emissions to the atmosphere from efw facilities are closely monitored for a wide variety of potential pollutants, including hydrochloric acid, nitrous oxides, sulphur oxides, dust, oxygen, total hydrocarbons, carbon monoxide, PCB's, dioxins and heavy metals. The Environment Agency makes sure that emissions from efw facilities are kept well below stringent levels set by UK and EU legislation. In this way, pollution is reduced to a level where it does not pose a significant risk to public health or the environment. Recent studies have reported that the potential for health effects from municipal waste incinerators that operate to Environment Agency emission standards is now so low as to be negligible.
Emissions from efw facilities are often significantly lower than emissions from other sectors. For example:
| Dioxins |
In 1999, efw plants contributed 0.8% of total regulated dioxin emissions compared with power stations (4.7%), iron and steel industry (13.1%), domestic heating (19.4%). |
| Dioxins |
Dioxin levels in processed IBA are typically < 10 ng/kg - comparable to typical urban soils in the UK - and lower than dust found in the streets of central London. |
| NOx |
In 1999, efw plants accounted for 0.2% of total UK NOx emissions, compared to road transport which accounted for 44.5% of the total. |
| CO2 |
Incineration of the biogenic fraction of municipal waste is a carbon neutral process, while CO2 emissions from the non-biogenic fraction are significantly lower than those from coal fired power stations, per kwh. |
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