Types of Energy from Waste (EfW) Facilities 

Different energy from waste plants are used to treat different types of waste. All are strictly monitored and must comply with European Directives on incineration. The local authorities or the Environment Agency ensure that all emission limits are met. Plants are regularly reviewed to ensure that emissions are reduced over time as the technology allows and as legal limits are tightened. 

Hazardous Waste Energy from Waste Plants
Hazardous waste plants primarily treat dangerous wastes from industrial sources, including the chemical and pharmaceutical industries, paint, food factories and metal processing operations.

There are two types of hazardous waste energy from waste plants: merchant or in-house. ESA’s Members are responsible for the two operational merchant hazardous waste plants in the UK. These facilities treat about 100,000 tonnes of hazardous waste each year between them. It is estimated that there are approximately 60 in-house energy from waste plants in the UK, but these are usually small, dedicated units. 

Municipal Waste Energy from Waste Plants
Municipal waste plants treat all types of municipal waste, burning the waste at high temperatures to reduce the volume of the waste and produce energy.

The capacity of the individual facilities range from 26,000 tonnes per annum (tpa) at Lerwick to 530,000 tpa at Edmonton in London, and together have a total capacity of 4.3 million tpa. EfW facilities in the UK currently recover value from approximately 8% of municipal waste.

Clinical Waste Energy from Waste Plants
There are currently around 250 energy from waste plants in the UK which deal solely with clinical waste, located mainly in hospitals. Clinical waste includes waste from hospitals, dentists, veterinary surgeries, nursing homes, etc. These wastes pose a significant threat to human health as they may contain waste tissue, blood, dressings, and other contaminated material. Chemical waste generally cannot be treated or disposed of by landfill or other processes.

Sewage Sludge Energy from Waste Plants
Currently, approximately 20% of sewage sludge (2.4 million tonnes) is incinerated in the UK. Incineration is usually carried out in multiple hearth or fluidisied bed systems, sometimes after mixing with municipal solid waste. The calorific value of dewatered sludges is typically sufficient to give self-sustaining combustion. 

Pyrolysis and Gasification
New technologies also offer the potential to recover other products from the waste stream which complete combustion would not allow. A number of these processes, such as pyrolysis and gasification, are under development at the moment, with a significant proportion focusing on biomass waste.

Pyrolysis involves heating waste in the absence of oxygen at temperatures of 400-800°C. The heat breaks down complex molecules and resultant gases are then passed into a combustion chamber where they are heated (in the presence of oxygen) at temperatures around 1250°C. The process produces a liquid oil which is used as a fuel.

Gasification involves heating wastes in a low-oxygen atmosphere to produce a gas with a low energy content. This gas can then be burned in a turbine or engine.

Combined Heat and Power
Combined Heat and Power (CHP) systems can make incinerators more energy efficient providing energy and heat for local communities and businesses. A number of the UK’s EfW facilities have a CHP system in place, but the absence of appropriate infrastructure restricts its use at other facilities. CHP is particularly suited to facilities which are close to new housing developments or industrial parks where a heating scheme can be incorporated at an early stage of construction.