ERI is the combustion of waste under controlled conditions in which the heat released is recovered for a beneficial purpose. This may be to provide steam or hot water for industrial or domestic users, or for electricity generation. Combined heat and power (CHP) incinerators provide both heat and electricity. The fuel value (calorific value) of household waste is about one third that of coal: as a rough guide, for every 100,000 tonnes of ERI capacity about 7 megawatts (MW) of electricity could be exported to the grid to meet the needs of about 11,000 homes.

The first fully functional waste incinerator was built in Nottingham, England in 1874. The facility operated for 27 years and the ash was used as a building material. Following the realisation that heat released by burning waste could be recovered for useful purposes, the world’s first waste fired electricity generation facility opened in 1885 in Shoreditch, London. Considerable development of the mechanisms for feeding waste and removing residues followed and, by 1912, there were 300 waste incinerators in the UK, 76 of which were generating power. The growth of incineration outside the UK got off to a slower start and was initially based on English technology. The City of Hamburg’s first waste incinerator began operation in 1895 and, shortly after incinerators were established throughout continental Europe, especially in Germany and major cities such as Brussels, Stockholm and Zurich.

The early designs of incinerator were based on batch-wise (ie non-continuous) operation. Control over the combustion conditions was ineffective and consequently a good deal of combustible material was left in the waste and stack gases prompting frequent complaints about smoke and smells. The development of mechanical grate systems providing automatic waste feeding and better control over combustion air supply led to significant improvements in combustion and emissions. Many of the patents for grate systems were registered in the 1920s and 1930s. Companies such as Von Roll and Martin in Germany and Voland of Denmark who developed these technologies remain key players in waste incineration today.

The amount of waste and its value as a fuel increased dramatically in the boom years following the Second World War with the growth of consumerism and increased use of throw-away items made of plastics and paper. This, coupled with the fact that waste avoidance and recycling were of no real concern, led to a major wave of construction of new waste incinerators in the 1960s and 1970s.

In the UK, about 40 municipal waste incinerators were built at this time. Only five of the larger plant were equipped to recover energy. The objective behind waste incineration at that time was to reduce the bulk of waste generated in the metropolitan areas to a small volume of sterile ash that would then cost less to transport to rural landfills. The abundance of low cost landfill sites has been one of the main reasons why ERI (and also recycling) has got off to a relatively slow start in the UK, compared with other EU countries without access to low-cost landfill. In contrast to the UK, in countries where energy efficiency had a high priority, most municipal waste incinerators recovered energy for district heating and/or power generation. Particular examples are Sweden, Germany and the Netherlands.

Most of the incinerators developed in the 1960s and 1970s had relatively rudimentary emission control systems compared to modern plant. 1989 saw the introduction of the two EC Directives introducing the first major EU-wide initiatives to raise environmental standards for waste incineration.

The 1989 EC Directives and UK legislation required all new incineration plant to comply with strict limits for dust, acidic gases and heavy metal emissions. Further tightening of EU-wide incineration emission limits is proposed with a new Directive likely to come into effect in 2000. All current and proposed plant will have to comply. The application of ERI as a significant treatment option for the UK was strongly advocated by the Royal Commission on Environmental Pollution in its Seventeenth Report.

Opportunities for ERI have improved as a result of changes in the electricity market. The most important of these is the Non Fossil Fuel Obligation (NFFO) introduced with the privatisation of most of the electricity supply industry in 1989. The NFFO allows the Secretary of State to require the regional electricity companies to contract to buy a specified amount of electricity from renewable energy sources, including ERI. The mechanism provides guaranteed access to the electricity grid (subject to payment of connection charges etc). There have been four orders under the NFFO so far. Government policy is to use the NFFO as a mechanism for building confidence and experience so that renewable energy technologies can eventually compete in the open market. Successive NFFO rounds have therefore shown a reduction in price towards market electricity prices. The NFFO is the principal means of working towards the target of 1,500MW generating capacity from renewable energy sources by 2000, of which ERI technologies are expected to contribute about one third.

The most widely deployed ERI process is called ‘mass burn’. Waste is burned on a moving grate in a boiler with little or no pre-processing. The boiler and grate system therefore have to be large and robust enough to withstand all conceivable articles in the waste stream.

The basic components of a plant are the:

• waste bunker and reception building where waste is delivered by road, potentially rail, or occasionally by river and stored prior to use
• combustion unit(s) which burn the waste
• heat recovery and power generation plant
• flue gas cleaning equipment which cleans the combustion gases prior to discharge to air
• ash collection facility
• exhaust stack which discharges the combustion gases to the air.

These main components are typically supported by facilities such as a gatehouse and weighbridge, storage facilities and silos for process materials, maintenance stores etc.

To ensure an even heat input, waste arising at the plant is mixed in the storage bunkers before being loaded, by means of a grab, into the grate feed chute. from here, the waste falls onto the moving grate system. Various designs are available but all have the purpose of mixing and moving the burning waste through the furnace so that by the time it is discharged into the ash pit all combustible material has been burnt. Air is introduced beneath and above the grate in carefully controlled amounts to ensure proper combustion. Additional fuelling with natural gas or oil may be required to maintain specified combustion conditions, especially during shutdown or start-up.

The hot gases from the secondary chamber are directed to a boiler to recover heat. During this stage the temperature drops as the heat is recovered as superheated steam through a series of heat exchangers. A nominal 550-650 kilowatt hours (kWh) of electricity or approximately 2,000kWh of heat per tonne of waste burned can be recovered. The efficiency of energy recovery depends upon the use - electricity or heat supply - and the plant design. Typically, about 10% of the electricity produced is used in running the systems within the plant and the rest - 90% - is available for export.

After the boiler the combustion gases are cleaned. There are a range of designs for flue-gas cleaning equipment but the system for a modern plant is likely to consist of the following:

• Acid gas scrubbing using a lime mixture injected into the gas stream which reacts to neutralise the acid gases such as sulphur dioxide, hydrogen fluoride and hydrogen chloride.
• Activated carbon injection to remove organic compounds such as dioxins and volatile metals such as mercury and cadmium.
• Particulate (dust) removal using an electrostatic precipitator or filters. These fine particulates are known as ‘fly ash’.
• Measures to reduce emissions of oxides of nitrogen. Those measures available range from controlling combustion conditions, eg by recycling some of the flue gas through the boiler. These simple measures will not, however, meet the new limit proposed in the draft EC Incineration Directive. To achieve these higher standards will require techniques such as Selective Catalytic Reduction (SCR) and selective Non-Catalytic Reduction (SNCR). Both are widely developed elsewhere in Europe. They rely on chemicals such as ammonia or urea injected into the flue gas to destroy oxides of nitrogen. SCR requires the use of special catalysts and natural gas burners to re-heat the flue gas to promote the reaction.

Emission control equipment can account for about 60% of the capital cost of a modern ERI plant.

Mass-burn facilities range in capacity from about 25,000 to over 1 million tonnes/year throughput but under UK conditions, plant below about 100,000 tonnes/year are likely to be economic, at least present.

The economics of ERI depend greatly on scale of operation. Plant capacities of 100,000-400,000 tonnes/year, typical of projects being developed in the UK, have net costs of about £47/tonne and £28/tonne respectively when selling electricity at market price. However, as with any large capital project, the economics are very sensitive to factors such as the discount rate and period of the loan. The structure of finance packages can therefore have significant effect project economics. In addition to income from the gate fee and power sales there are opportunities for selling recovered metal and possibly grate ash as a construction material.

There are presently seven mass-burn ERI facilities operating in the UK: at Nottingham, Edmonton, Sheffield, Coventry, Lewisham, Billingham and Tyseley. The SELCHP (South East London Combined Heat and Power) plant in Lewisham which opened in 1994 was the first of the totally new generation of ERI plant built since the 1970s. With a waste capacity of 420,000 tonnes/year the plant has a generating capacity of about 30MW and is equipped to supply hot water to neighbouring residences. New plant in Billingham and Tyseley have since opened and similar plant are under construction in Dudley, Stoke and Wolverhampton.

An alternative approach to the widely deployed mass-burn systems is to first sort the household waste to remove recyclable materials and wet putrescible materials. The combustible residue is then shredded and either burnt directly as a coarse ‘floc’ - so-called coarse refuse-derived fuel (CRDF) - to compressed into pellets- densified RDF (dRDF). This process and burn approach can therefore potentially integrate well with recycling and anaerobic digestion options at an MRF. RDF pellets can be sold as a distributable fuel to industrial users - either as a replacement for coal or for co-firing with it in suitable boilers. However, the development of dRDF markets in the UK did not live up to expectations at the time the technology was developed in the 1970s and 1980s. Since then, coal prices have fallen and natural gas has become widely available for industrial users, making it difficult for dRDF to compete, so limiting the market for dRDF pellets.

Interest has now moved towards cRDF fired directly in fluidised bed combustors. This approach reduces the need for the energy-intensive pelletisation steps and for fuel distribution.

Most experience with these systems resides in Scandinavia and Japan. CRDF technologies using fluidised beds are well established for waste throughputs of 75,000 to 200,000 tonnes/year but to date no plant based on this approach is currently operating in the UK, although a 120,000 tonnes/year facility is under construction at Dundee. Net costs are expected to be similar to mass-burn facilities.

In addition to these combustion options, interest has increased recently in gasification and pyrolysis. In the former the waste is heated in a low oxygen atmosphere to generate a low heat content gas for burning in an engine or turbine. In pyrolisis, the waste is heated to high temperature in the absence of oxygen to produce a secondary fuel product. Large-scale plant for household waste treatment by these processes have recently begun operation in Germany. Currently disposal costs are high in comparison with conventional plant. These technologies have yet to establish a sound track record of performance at commercial (>100,000 tonnes/year) scales of operation and none are currently planned for the UK.

Environmental impacts arise from the construction of an ERI plant and its operation. Constructional impacts are similar to those of other large industrial and waste developments. They include additional traffic, noise, visual impact and potential damage to wildlife and cultural heritage. Since most developments will take place on brownfield sites, the last two of these impacts may be less significant and the others can be minimised by careful planning and site management.

Amenity impacts arise from the construction of an ERI plant and its operation. Constructional impacts are similar to those of the large industrial and waste developments. They include additional traffic, noise, visual impact and potential damage to wildlife and cultural heritage. Since most developments will take place on brownfield sites, the last two of these impacts may be less significant, and the others can be minimised by careful planning and site management.

Amenity impacts during operation include vehicle movements, odour, noise and visual intrusion. All of these impacts can be controlled and minimised by careful siting, design and operation of the facility. Other environmental impacts may arise from solid, liquid and gaseous emissions and, in addition, some impacts associated with alternative waste management options, such as landfilling, can be avoided by diverting waste to an ERI facility. These issues are discussed in more detail below.

Solid residues consist of ash and residues from the air pollution control plant. Some gas scrubbing equipment in use elsewhere in Europe uses liquids as the absorbent for acid gases, so generating large volumes of salty water for discharge or treatment. All current and proposed UK municipal waste incinerators use dry or semi-dry scrubbers, so no appreciable amount of liquid discharge is produced. Such discharges would, in any case, be subject to regulation by the Environment Agency.

The main component of the solid residue is grate ash - also known as bottom ash, which represents about 30% by weight of the original waste, and about 10% by volume. Bottom ash is an inorganic, sterile material with the consistency of sandy gravel containing about 10-15% of ferrous metals. After the ash is discharged from the grate, it is quenched in water before metals are segregated by magnets for recycling. The remaining ash is then disposed of to landfill or can be used in road-building and construction. In the UK most ash is disposed of to landfill. This contrasts with countries such as Switzerland, Germany and Sweden where there has been a greater re-use of bottom ash, in particular for roadbase construction, car park bases etc. As the cost of landfill increases it is likely that the UK will see greater pressure to re-use ash.

Fly ash arises from the particulate removal during the gas cleaning. It consists of firm particulates in the gas stream and the reagents such as lime or activated carbon and salts removed from the flue gas stream. It represents about 4% by weight of the input waste. The fly ash is conditioned with water and can be pre-treated to reduce or immobilise potentially harmful constituents such as heavy metals. Such pre-treatments include mixing the fly ash with a binding agent such as cement or bitumen. The pre-treated ash is then disposed of as ‘special’ hazardous waste in a designated landfill engineered to prevent escape of dissolved materials. Ash is usually bagged before removal to prevent the escape of dust. Ash can also be compacted, for example by briquetting to improve handling and storage characteristics.

The following table compares current emission limits and those to come in under the proposed EC Incineration Directive due to take effect in 2000. It should be noted that some countries, such as Germany and the Netherlands, have already adopted equivalent standards and have plant operating well within them.

Measurements of contaminants in a gas at such levels are the limits of detection which modern equipment can achieve. Particulates and hydrogen chloride are monitored continuously. For continuous monitoring the emission standards are complied with if 95% of the hourly average readings for each 24 hours do not exceed the value and the peak hourly average does not exceed 1.5 x the value.

The metals, hydrogen fluoride, sulphar dioxide, oxides of nitrogen and volatile organic carbon have to be monitored at least quarterly for the Environment Agency. Annual measurements are required for dioxins. Measuring such small amounts of dioxins continuously is not possible as the concentration of dioxins in the stack gas is well below the sensitivity of current instrumental analytical techniques.

The height of the stack is prescribed and is calculated using a model approved by the Environment Agency which takes into account local meteorological data, local topography, other local emissions, and nearby buildings and structures, and makes allowance for possible plant malfunctions.

(a) All concentrations are given in units of milligrams per normal cubic metre of stack gas, corrected to 11% oxygen at 273K and 101.3kPa, except dioxins, which are expressed in nanograms of international toxic equivalent (I-TEQ) per normal cubic metre of stack gas. The measurement units are outlined in further detail in the section headed ‘Measurements’.

(b) Limits for new incineration plant according to Directive 89/369 EEC, which have been adopted for current UK limits set out in Chief Inspector’s Guidance to Inspectors: EPA (1990) Process Guidance Note IPR5/3. Values relate to seven day averages.

(c) Proposed limits in the Draft Directive on the Incineration of Non-hazardous Wastes, April 1997. Values relate to 24 hour averages.

‘Dioxin’ is the short hand name given to a family of about 200 chlorinated organic compounds known chemically as polychlorinated dibenzo para dioxins and the closely related furans. Dioxins are of concern because of the extremely high toxicity shown by some members of the class.

Dioxins are found throughout the world although they have never been intentionally produced on an industrial scale. They are released into the environment as contaminants in other products, notably some herbicides and wood preservatives. Dioxins are also formed in trace amounts in combustion processes, such as power plant, cement kilns, diesel vehicles, buses, open fires in the home, bonfires barbecues, cigarettes, jet engines, forest fires and waste incinerators.

It is generally accepted that high combustion temperatures in the presence of an adequate supply of oxygen provides a good basis for destroying dioxins that come into an incinerator as contaminants in the waste and for minimising their re-formation in the hot gases. This was the rationale for specifying detailed combustion conditions under current UK and EU Regulations. Dioxins can also be formed in the cooling gas stream as it leaves the incinerator furnace. This process can be minimised by reducing the time the combustion gases spend at the critical temperature range (about 200-450°C) at which dioxin formation is most rapid, and by reducing contact with fly ash, which may help to accelerate formation.

Since dioxins contain chlorine, a great deal of debate has revolved around the issue of how effective the removal of chlorine-containing materials (such as PVC) from the waste stream would be in reducing their formation. The problem is that chlorine is present in one form or another in virtually all materials and so there will always be a vast excess available compared with the tiny amounts that may become incorporated into dioxin. Trials on laboratory, pilot and full scale plant have all confirmed the lack of beneficial effects on dioxin emissions, and therefore this cannot be used as a strategy for controlling dioxin emissions.

There are a number of important issues to be addressed in considering how dioxins are measured. Firstly, the number and position of the chlorine atoms in a dioxin molecule have a very powerful influence on its toxicity. In addition, most sources of dioxin produce a very wide range of the possible forms. because of this, it is customary to refer to dioxin concentration sin terms of the equivalent cncentration of the most toxic form, 2,3,7,8- tetra-chloro dibenzo para dioxin, (2,3,7,8-TCDD). Several such equivalent schemes have been devised but the one in most common use is the I-TEQ. which is used here.

Secondly, the amounts of dioxin in environmental materials are extremely small - measuring then is a specialised task. There are at present no monitors that can measure dioxin emissions on a continuous basis at the concentrations produced by ERI plant. Samples have to be collected and then extracted, allowing the tiny amounts of dioxin to be concentrated up to measurable amounts, before analysis.

Scientists refer to dioxin concentrations in units of weight expressed as fractions of a gram. A teaspoon of sugar would weigh about five grams. For comparison purposes, the maximum amount of concentration of dioxins in untreated flue gas (ie before any form of gas cleaning) is about 10 nanograms per cubic metre, a nanogram being one billionth of a gram (1/1,000,000,000 gram or 10^-9 gram). Concentrations in environmental examples are often expressed in units of pico-, or even femto-grams, equivalent to a thousand billionth (1/1,000,000,000,000 or 10^-12) and million billionth (1/1,000,000,000,000,000 or 10^-15) of a gram, respectively. However, the issue is not about how big or small are the amounts of dioxin produces, but rather their possible effects. This is discussed further, below.

In 1995 a report for Her Majesty’s Inspectorate of Pollution (now part of the Environment Agency) examined the sources of dioxins in the UK. It estimated that with the new controls on incinerators post-December 1996, ERI plant would account for a maximum of about 15 grams I-TEQ, ie about 4-14% of the total dioxin sources. Emissions from incinerators are set to fall further with the introduction of the proposed new EC Incineration Directive in 2000, which proposes an emission limit of 0.1 nanogram per normal cubic metre of stack gas. However, dioxins will also be present in waste materials. These may be released or emitted during other waste processing activities, eg recycling, composting.

A more important issue is not the contribution of incinerators to the total environmental ‘burden’ but what the impact or effect of this biurden is. The location of the plant relative to areas of food production (the most important route by which dioxins enter the human body is food), the height of the stack and buoyancy of the releases, and the frequency of the release are more important than the absolute amount of dioxins released. Studies in the USA, Germany and the UK suggest that an individual who might have maximum exposure to dioxins will only derive about 5% of the total dioxins to which he or she is exposed from municipal waste incinerators.

Dioxins are extremely resistant to decomposition, virtually insoluble in water but highly soluble in fats. Because of these properties they are able to accumulate in the food chain (by concentrating in fats) and are now detectable (albeit at extremely low concentrations) in human and animal tissue from all over the world. Whilst dioxins released into the air from combustion sources can enter humans from absorption through the lungs (inhalation) or from deposition onto the skin, the major route is from deposition onto herbage, followed by uptake into grazing animals. It is the food chain which is the most significant in terms of human intake, accounting for 90% of all exposure: meat and dairy products are significant sources. The Ministry of Agriculture Fisheries and Food (MAFF) carries out surveys of the levels of dioxins in food, including milk. The level of dioxins is higher in breast milk than in cows milk, demonstrating the accumulation through the food chain. Accumulation in breast milk is of particular concern since this is often the only source of food for young babies. Studies have estimated the total daily intake of dioxins by the average UK consumer, noting a decline to 69 picograms (pg) TEQ/person/day in 1992, reflecting changing dietary habits and a fall in the average fat content of foodstuffs.

Health problems associated with dioxins date back to the early 20th century in Germany when chemical workers making pesticides were exposed to large doses of the compound and developed chloracne, a disfiguring but curable skin disorder. Most understanding of the toxicity of dioxins comes from such occupational and accidental exposure or from the study of laboratory animals. For humans, all of the actual incidents of exposure to dioxins so far studied have involved sources other than incinerators, and have been complicated by the fact that individuals have been exposed to a mixture of chemicals, not just dioxins.

In animals, dioxins are known carcinogens (cancer-inducing agents) which modify cell growth. The World Health Organisation(s) (WHO’s) International Agency for Research on Cancer (IARC) had classified the most toxic member of the dioxin family (2,3,7,8-TCDD) as a Group 2 carcinogen, ie possibly carcinogenic in humans. There is evidence from experiments on laboratory animals, including monkeys, that dioxins can adversely affect reproduction and the immune system. However, laboratory studies show wide variations between different species in their susceptibility to dioxins. In the light of evidence showing that 2,3,7,8-TCDD causes cancer in experimental animals at tissue concentrations similar to those in heavily (ie occupationally) exposed humans, IARC in 1997 revised its classification to that of a known human carcinogen.

There are two approaches by which the effects of dioxins are assessed:

• By deriving an Acceptable or Tolerable Daily Intake (TDI). This approach assumes that there is a threshold dose below which no ill effects occur. This is applied to non-genotoxic carcinogens - ie those that do not directly affect genetic material.
• By assuming a no-threshold dose, ie that effects are possible with any intake. This is applied for genotoxic carcinogens that do affect genetic material.

The first approach has been adopted by the WHO and by all European countries including the UK. The second approach is that used by the United States Environmental Protection Agency (USEPA). Both approaches start from the same point which is to determine the manner in which an adverse effect varies according to the dose of the chemical received, and to extrapolate from the high doses which are measured in laboratory experiments to the low doses experienced in the environment and the dose at which no adverse effect is observed.

Currently the WHO and the UK Government accept a no-effect level in animal studies with rats of 1 nanogram per kilogram of body weight per day (1ng/kg.bw/day), Applying a safety factor of 100 for the extrapolation from rats to humans, a TDI of dioxins has been set at 10pg/kg.bw/day. However, because dioxins accumulating in the body take a long time to break down, the UK’s preferred approach is not to regard the TDI as being strictly applicable on a daily basis, but as a time-weighted average tolerable intake, say over a period of a week (which would give a TDI of 70pg/kg.bw/week).

It has been calculated that the daily intake of dioxins for a breast-fed child is of the order of 100pg/kg.bw/day. However, the Government’s medical advisory committee has endorsed the view of the WHO that any potential risks from exceeding the TDI for a relatively short period in early life are far exceeded by the considerable benefits of breast-feeding.

The US approach assumes that there is no safe level of exposure except zero exposure (which of course is impossible given the huge number of uncontrollable sources of dioxins). The USA has identified what it refers to as a virtually safe dose (the dose which has a 1 in 1 million chance of causing cancer: ie a 1 x 10^-6 risk. In 1994 the USEPA’s assessment discussed the potential for adverse effects in human metabolism and reproduction. However, it concluded that there was no indication of increased disease in the general population attributable to dioxins.

Opinions amongst the US scientific community have been mixed., In January 1995 the UK Royal Commission on Environmental Pollution issued a press release which stated that the commission had reviewed its original conclusions on dioxins in the light of the US report and that nothing had emerged which would lead it to alter the views expressed in the Seventeenth Report about the environmental acceptability of incinerators which would meet present day standards for emissions.

The UK Committee on the Toxicology of Chemicals in Food, Consumer Products and the Environment (COT) concluded that all available evidence did not support the USEPA approach of treating dioxins as genotoxic carcinogens and in September 1995 stated that there was no evidence that necessitated alteration of the previously agreed TDI of 10pg/kg.bw/day 2,3,7,8-TCCD TEQ.

The focus on dioxins internationally has sometimes led to a failure to recognise that other chemicals, which are components of stack emissions, have the potential to cause adverse health effects. The heavy metals - mercury and cadmium - can also be taken up via the food chain. Fish and shellfish are the dominant dietary source of mercury, and vegetables and crops of cadmium. There is a general policy to reduce the intake of heavy metals as they can interfere with human growth and metabolism. No effects on health, however, have been linked to the release of heavy metals from incineration plant.

The acidic gases (sulphar dioxide, nitrogen oxides, hydrogen fluoride and hydrogen chloride) do not accumulate in the environment. Their main health effects are respiratory irritation, especially in sensitive people such as those who suffer from asthma. However, in the ambient air concentrations resulting from emissions from an incinerator it is most unlikely that any effects would be experienced.

Much attention has recently been focused on the impacts of exceedingly fine particles that can penetrate deep into the lungs. Those less than 10 micrometres in diameter are referred to as PM.

Exposure to small particulates is associated with both acute and chronic (long-term) health effects, particularly in people with existing respiratory disease. The UK has recently set an exposure value of 50 micrograms/cubic metre (m g/m³) as a 24 hour average. However, emissions form incinerators represent very small sources of such particles in comparison with other sources, notable emissions from diesel engines).

Several epidemiological studies have been carried out in areas surrounding waste incineration plant in the UK. They have been undertaken in response to public concerns about possible effects linked to evidence of what appears to be higher than normal incidences of cancer in some areas. The study by the Small Area Health Statistics Unit showed an unexplained excess of liver cancer around incinerators. However, none of these studies has proven any link between the incinerators and healthy. It is also important to understand that all the studies have been conducted in relation to old plant which were operating under much less stringent emission standards than are now required, and to which current plant are operating.

Most planning applications for new ERI plant will need to be accompanied by an Environmental Statement. The potential air and health effects of the emissions would be addressed by such an assessment. Increasingly these statements have included a risk assessment. This models the release of emissions in the environment and allows a site-specific assessment of the potential risks to health from the different chemicals. Importantly the assessment should include monitoring of the existing environment before the incinerator is built. This allows comparison with the situation when the plant is operating.

In May 1996 the Environment Agency published a report presenting a risk assessment of dioxin releases from municipal waste incineration processed, including ERI plant. The report concludes that such plant operating to the new pollution control standards will not pose a health risk to people living nearby, irrespective of the location and size of the plant, the profile of the people concerned (such as breast-feeding children) or the activities in the surrounding area (such as other industrial processes).

All incinerators, including ERI plant, burning household waste are subject to authorisation by the Environment Agency under integrated pollution control. Process guidance notes issued by the Agency set out the emission standards relevant to such plant and provide technical guidance on operation and equipment. An authorisation is only granted after the operator has presented an assessment to the satisfaction of the Environment Agency of the total impact of releases to air, water and land. Applications for authorisation are put on a public register to allow for representations by the public.

Monitoring of emissions is carried out by the operator, subject to checking by the Environment Agency. Monitoring data are replaced on public registers which are open for inspection.

The consideration and monitoring of the authorisation by the Agency also includes reference to the management techniques (not just technologies) used to control the plant.

Most of the carbon in household waste comes from paper, cardboard etc produced from non-fossil fuel sources. Energy from waste can therefore displace electricity and/or heat generated from fossil fuels such as coal, thus making a small contribution towards reducing the emissions of the ‘main ‘greenhouse’ gas carbon dioxide. The magnitude of this effect does depend on the fuel that is displaced by ERI. This is largest if it is old coal-burning plant, but much less if ERI replaces generating plant equivalent to the current fuel mix.