Carbon dioxide

CO2

Molar mass 44.01 g/mol
Lifetime in atmosphere No single lifetime can be given
Global Warming Potential over 100 years 1
Estimated emissions in 2008 51,762,916 Gg
Atmospheric concentration in September 2013 393,510,000 ppt

Nearly all of the carbon content in incinerated waste is emitted to the atmosphere as carbon dioxide. Municipal solid waste contains approximately the same mass fraction of carbon as does carbon dioxide itself (27%), so incineration of 1 tonne of waste is estimated to produce approximately 1 tonne of carbon dioxide.

Carbon dioxide emitted by human activity is of course the main cause of global warming leading to climate change. Under the Climate Change Act 2008, the UK is committed to reduce greenhouse gas emissions from 1990 levels by at least 80% by 2050. In 1990, emissions from energy consumption were 10.5 tonnes of carbon dioxide per capita, so the target is slightly over 2 tonnes per capita.

In 2011, UK emissions from energy consumption were 8 tonnes per capita, the reduction from 1990 largely due to the replacement of coal by gas in electricity generation. The Exeter Incinerator is designed to accept up to 60,000 tonnes per year of waste, from Exeter and the immediate surrounding area in Devon. With a population of about 120,000, that means 0.5 tonnes of carbon dioxide added to every person’s carbon budget. But suppose the Incinerator replaced some carbon emissions from other energy plant……

Incinerators have electricity generation efficiencies of 14-28%. The waste heat can be used in a district heating network, giving efficiencies higher than 80%. The Exeter Incinerator will initially provide electricity to the national grid, and has the potential to export heat but only if a district heating network is established on the Marsh Barton estate.

So the Incinerator will produce electricity at a substantially lower efficiency than the rest of the national grid, and displace lower carbon alternatives.

2,3,7,8-Tetrachlorodibenzo-p-dioxin

Dioxin

Polychlorinated dibenzo-p-dioxins (PCDDs; known colloquially and inaccurately as dioxins) are subject to the European Waste Incineration Directive, which puts strict limits on emissions to air. Incineration is controlled to minimise their production, and the flue gas is treated post-combustion. The resulting toxic fly ash must be handled as hazardous waste.

Emissions of dioxins and furans from an incinerator typical of those currently operating in the UK (230,000 tonnes per year) are approximately equivalent to emissions from accidental fires in a town the size of Milton Keynes (population 230,000). That is, emissions from the Exeter Incinerator will be equivalent to half the emissions from accidental fires in Exeter.

The structure of dioxins comprises two benzene rings (six carbon atoms) joined by two oxygen atoms. Chlorine atoms may be attached to this structure at any of positions 1–4 and 6–9 in the above picture, which gives 75 flavours. Hydrogen atoms are attached to the remaining positions.

Dioxins are commonly regarded as highly toxic compounds that are environmental pollutants and persistent organic pollutants. Of the 75 flavours, the seven below are considered toxic by the World Health Organization (WHO). 2,3,7,8-Tetrachlorodibenzo-p-dioxin* became known as a contaminant in Agent Orange, and is the most toxic of all. It is therefore designated the reference molecule for rating toxicity.

Flavour (DD stands for
dibenzo dioxin)

Formula

WHO Toxicity
Equivalency Factor

2,3,7,8-Cl4DD

C12H4Cl4O2

1

1,2,3,7,8-Cl5DD

C12H3Cl5O2

1

1,2,3,4,7,8-Cl6DD

C12H2Cl6O2

0.1

1,2,3,7,8,9-Cl6DD

C12H2Cl6O2

0.1

1,2,3,6,7,8-Cl6DD

C12H2Cl6O2

0.1

1,2,3,4,6,7,8-Cl7DD

C12HCl7O2

0.01

Cl8DD

C12Cl8O2

0.0003

For more information, see the Wikipedia articles about polychlorinated dibenzodioxins and specifically 2,3,7,8-Tetrachlorodibenzo-p-dioxin.

*The ‘p’ stands for ‘para’, indicating the oxygen atoms are opposite each other. The oxygen atoms could be next to each other, which would be indicated by ‘o’ for ‘ortho’, but this molecular configuration is unstable.

2,3,4,7,8-Pentachlorodibenzofuran

Furan

Polychlorinated dibenzofurans (PCDFs; known colloquially as furans) are subject to the European Waste Incineration Directive, which puts strict limits on emissions to air. Incineration is controlled to minimise their production, and the flue gas is treated post-combustion. The resulting toxic fly ash must be handled as hazardous waste.

Emissions of dioxins and furans from an incinerator typical of those currently operating in the UK (230,000 tonnes per year) are approximately equivalent to emissions from accidental fires in a town the size of Milton Keynes (population 230,000). That is, emissions from the Exeter Incinerator will be equivalent to half the emissions from accidental fires in Exeter.

The structure of furans comprises two benzene rings (six carbon atoms) joined directly and by one oxygen atom. Chlorine atoms may be attached to this structure at any of positions 1–4 and 6–9 in the above picture, which gives 135 flavours. Hydrogen atoms are attached to the remaining positions.

Of the 135 furan flavours, the ten below exhibit dioxin-like properties and are given toxicity ratings by the World Health Organization (WHO). Furans are commonly regarded as highly toxic compounds that are environmental pollutants and persistent organic pollutants.The reference molecule for rating toxicity is 2,3,7,8-Tetrachlorodibenzo-p-dioxin.

Flavour (DF stands for
dibenzo furan)

Formula

WHO Toxicity
Equivalency Factor

2,3,7,8-Cl4DF

C12H4Cl4O

0.1

1,2,3,7,8-Cl5DF

C12H3Cl5O

0.03

2,3,4,7,8-Cl5DF

C12H3Cl5O

0.3

1,2,3,4,7,8-Cl6DF

C12H2Cl6O

0.1

1,2,3,7,8,9-Cl6DF

C12H2Cl6O

0.1

1,2,3,6,7,8-Cl6DF

C12H2Cl6O

0.1

2,3,4,6,7,8-Cl6DF

C12H2Cl6O

0.1

1,2,3,4,6,7,8-Cl7DF

C12HCl7O

0.01

1,2,3,4,7,8,9-Cl7DF

C12HCl7O

0.01

Cl8DF

C12Cl8O

0.0003

For more information, see the Wikipedia article about dioxins and dioxin-like compounds.

3,3′,4,4′,5-Pentachlorobiphenyl

PCB

Polychlorinated biphenyls (PCBs, not to be confused with printed circuit boards) are not subject to the European Waste Incineration Directive, but emissions can be controlled in the same way as dioxins and furans; incineration is controlled to minimise their production, and the flue gas is treated post-combustion.

The structure comprises two joined phenyl rings (six carbon atoms). Chlorine atoms may be attached to this structure at any of positions 2-6 and 2′-6′ in the above picture, which gives 209 flavours. Hydrogen atoms are attached to the remaining positions.

Of the 209 PCB flavours, the twelve below exhibit dioxin-like properties and are given toxicity ratings by the World Health Organization (WHO). PCBs are commonly regarded as highly toxic compounds that are environmental pollutants and persistent organic pollutants.The reference molecule for rating toxicity is 2,3,7,8-Tetrachlorodibenzo-p-dioxin.

Flavour

Formula

WHO Toxicity
Equivalency Factor

3,3′,4,4′-Tetrachlorobiphenyl

C12H6Cl4

0.0001

3,4,4′,5-Tetrachlorobiphenyl

C12H6Cl4

0.0003

2,3,3′,4,4′-Pentachlorobiphenyl

C12H5Cl5

0.00003

2,3,4,4′,5-Pentachlorobiphenyl

C12H5Cl5

0.00003

2,3′,4,4′,5-Pentachlorobiphenyl

C12H5Cl5

0.00003

2′,3,4,4′,5-Pentachlorobiphenyl

C12H5Cl5

0.00003

3,3′,4,4′,5-Pentachlorobiphenyl

C12H5Cl5

0.1

2,3,3′,4,4′,5-Hexachlorobiphenyl

C12H4Cl6

0.00003

2,3,3′,4,4′,5′-Hexachlorobiphenyl

C12H4Cl6

0.00003

2,3′,4,4′,5,5′-Hexachlorobiphenyl

C12H4Cl6

0.00003

3,3′,4,4′,5,5′-Hexachlorobiphenyl

C12H4Cl6

0.03

2,3,3′,4,4′,5,5′-Heptachlorobiphenyl

C12H3Cl7

0.00003

For more information, see the Wikipedia articles about polychlorinated biphenyls and dioxins and dioxin-like compounds.

Nitrogen oxides

NOx

Nitric oxide (NO) and nitrogen dioxide (NO2) are subject to the European Waste Incineration Directive, which puts strict limits on emissions to air. But removal of nitric oxide by incinerators is only about 60% effective and the remainder may be converted to nitrogen dioxide to form smog and acid rain.

Nitrogen dioxide has a variety of health impacts, such as higher incidence of respiratory symptoms in children, asthma, chronic obstructive pulmonary disease, lung cancer, heart disease in those over 65, and abnormally elevated immune and allergic responses. When nitrogen dioxide is combined with fine particulates and carcinogenic heavy metals (in particular cadmium), the effects on lung cancer are likely to be more potent.

Particulate matter

PM2.5

Incinerators may emit fine particles, and the EU Waste Incineration Directive puts limits on emissions to air of heavy metals, dust, and total organic carbon, among other pollutants. Therefore, incinerators operate a filtration system to control particulate emissions.

Emissions of particulate matter from an incinerator typical of those currently operating in the UK (230,000 tonnes per year) are approximately equivalent to emissions from a 5 km stretch of typical motorway. That is, emissions from the Exeter Incinerator will be approximately equivalent to the emissions from the M5 between junctions 29 and 30.

PM10 is defined as the mass of particles of less than about 10 microns (or one-hundredth of a mm) in diameter per cubic metre of air. PM2.5 is the mass of particles of less than about 2.5 microns in diameter per cubic metre of air. PM10 and PM2.5 samples from around the world can vary substantially in their chemical composition and size distribution, and it is possible that associated metals and ultrafine particles are important. Yet international and national regulations are currently framed in terms of mass concentrations instead of, say, the chemical (metallic) composition, the number of particles and total surface area of particles per unit volume of air, or the capacity of particles to generate free radicals.

Long term exposure to particles affects the risk of mortality, especially from cardiovascular disease and from lung cancer. Short-term increases in concentrations cause increases in deaths from and hospital admissions for heart attacks and respiratory disease, and related symptoms.

Mercury and other metals

Hg

Of the heavy metals, mercury is a major concern due to its toxicity and high volatility. It is subject to the European Waste Incineration Directive, which puts limits on emissions to air, so the flue gas is treated post-combustion. The resulting toxic fly ash must be handled as hazardous waste.

Acute exposure to mercury vapour can lead to irritation of the lungs, coughing, chest pain and shortness of breath, and central nervous system (CNS) effects such as tremors and mood changes. Chronic exposure also leads to CNS effects such as increased excitability, excessive shyness and irritability.

Cadmium emissions from an incinerator the size of the Exeter plant are approximately equivalent to one-eightieth of the emissions from a medium sized UK coal-fired power station.

Acute inhalation exposure to cadmium can lead to irritation of the lungs. Chronic exposure can cause a build-up of cadmium in the kidneys that can lead to kidney disease.

Although zinc poses no documented health risks, if its physical state is altered during use then health risks can be created. Inhalation of metallic oxide fumes can lead to metal fume fever.

Non-ferrous and/or ferrous metals are recovered (separated from Municipal Solid Waste or Incinerator Bottom Ash) and recycled from most incinerators in the UK.

Hydrogen halides

HHal

Hydrogen fluoride and hydrogen chloride, but not hydrogen bromide, are subject to the European Waste Incineration Directive, which puts strict limits on emissions to air.

They are acidic gases primarily released to air from combustion of fuels which contain trace amounts of fluoride, chloride or bromide. They are highly corrosive, and inhalation of air containing low levels of hydrogen chloride can cause throat irritation or asthma. Exposure to higher levels may result in effects including rapid breathing, blue colouring of the skin, fluid accumulation in the lungs and in extreme cases severe swelling of the throat, suffocation and death. Inhalation of air containing hydrogen fluoride can cause irritation of the eyes, nose and throat. Exposure to high levels may cause muscle spasms and can damage the lungs and heart and in extreme cases can result in death.