Waste Technologies
This section provides a brief guide to the key waste technologies. These are the main types of treatment that can be used to deal with our waste.
Each technology guide provides information on what waste types can be inputted into the technology, the treatment process, and the outputs. Each guide also provides summary information about the potential impacts of the technology, the regulations that apply, and sources of further information.
Anaerobic Digestion
Anaerobic digestion (AD) is a managed biological process in which biodegradable waste is broken down by naturally occurring micro-organisms in the absence of oxygen to produce a stabilised residue. AD can reduce the volume of waste by approximately 60%. While it has not been used for treatment of Biodegradable Municipal Waste (BMW) in the UK, the practice is increasingly common in Europe. In Scotland there is a plant currently under construction in the Western Isles for the treatment of BMW.
AD may be combined with a range of other waste treatment technologies. It can be used after waste has been treated at an MRF separation facility, and in conjunction with waste treatment technologies for the non-organic fraction of waste.
Inputs
BMW, agricultural residues, sewage sludge, and industrial organic wastes. Food wastes may be treated only if the plant is compliant with Animal By-Products (Scotland) (SSI 2003/411). Ideally this process should treat only segregated biodegradable waste. Mixed waste can be treated by anaerobic digestion; however this may result in contamination of the liquid and solid fractions which can make them less suitable as soil conditioners or fertilisers.
Process
Waste is collected and brought to the site where it is pre-treated to remove non-biodegradable materials such as plastics, metals and stones, and shredded to a uniform size in order to aid digestion. The biodegradable materials are transferred to an enclosed, oxygen free, warmed container. Bacteria then digest the waste, which can take from 12-30 days, producing biogas. The digested matter, or digestate, is then pumped into a storage tank, where biogas continues to be produced. The residual digestate can then be separated to produce fibre and liquor, which must be refined for use in horticulture or agriculture. Material going to landfill is stabilised and compacted in order to reduce leachates, dust and odour when it is in landfill. The waste water, which is high in nitrates, should be treated.
Outputs- 30-60% is converted to biogas, which is rich in methane and can be used to generate electricity or heat;
- Fibre, which is nutrient rich and can potentially be used as soil conditioner, though the quality of this product and the certainty of end use depends heavily on the waste input and the extent of refining;
- Liquor can potentially be used as a liquid fertiliser, though as with fibre, the quality of this product and the certainty of end use depends heavily on the waste input and the extent of refining;
- Waste water and water vapour which may be recycled for the dilution of fresh waste is sent to a wastewater treatment plant, or applied to farmland as liquid fertiliser; and
- Non-organic waste (depending on contamination of input).
Regulation
- EU Landfill Directive (99/31/EC) requires a reduction in the amount of BMW to landfill.
- Integrated Pollution Prevention and Control Directive (96/61/EC) was created to prevent or minimise emissions to air, water and soil, as well as waste.
- Animal By-Products Regulation (Scotland) (SSI 2003/411) establishes health rules concerning animal by-products not intended for human consumption and applies to food waste that is composted.
- Public Participation Directive (2003/35/EC) requires that the application and decision document for a waste treatment installation permit must be made available to the public for their comment.
Further Information
Introductory:
Intermediate:Detailed:Gasification
The key aspect of gasification is that it is done in a low-oxygen atmosphere thus avoiding direct combustion. Gasification is the controlled combustion of waste at temperatures up to 1400oC producing a synthetic gas known as syngas which can then be used to generate electricity and/or heat. Gasification can reduce the volume of waste by up to 90%. Gasification is a relatively new technology for the treatment of Municipal Waste (MW). There are currently no gasification plants treating MW in Scotland; however there is a fully operational (but not full scale) demonstration plant in Bristol that combines both Gasification and Pyrolysis. Gasification can be combined with a range of other waste treatment technologies.
Inputs
Gasification can treat MW and other waste types including commercial and industrial waste, and clinical waste.
Process
Waste is collected and delivered to the site where it is pre-treated to remove non-combustibles such as glass and metal, remove excess moisture, and sometimes shredded to a uniform size. It is then fed into the gasification reactor where it is burnt. The unburned residue, or bottom ash, from the non-organic fraction of MW is stabilised and is deposited into a quench tank. Magnets remove any ferrous metals from the ash for recycling and the remaining ash may be recycled for use in construction. The combustion process also produces carbon which is transformed into syngas. This can be used at the plant to generate electricity and/or heat, or can be refined, using a system of scrubbers and cleaners, to produce a highly efficient gas which can be further scrubbed of pollutants for combustion on-site or transported to other energy generation sites. Gasification plants are able to operate at less than 100% of capacity and do not need to run 100% of the time, as start-up periods are relatively short, so there is flexibility when there is a decline waste availability.
Outputs
1 tonne of MW produces approximately:- 150-300kg of ash residue for use in construction or landfill;
- 20kg of hazardous waste to landfill; and
- Syngas
Regulation- EU Landfill Directive (99/31/EC) requires a reduction in the amount of BMW to landfill. The Directive also requires Member States to set up a national strategy for the implementation of these targets.
- Integrated Pollution Prevention and Control Directive (96/61/EC) was created to prevent or minimise emissions to air, water and soil, as well as waste.
- Waste Incineration (Scotland) Regulations (SSI 2003 No170) introduced strict regulatory controls and set minimum technical requirements for waste incinerators.
- Public Participation Directive (2003/35/EC) requires that the application and decision document for a waste treatment installation permit must be made available to the public for their comment.
Further Information
Introductory:
- www.defra.gov.uk/environment/waste/wip/newtech/pdf/att.pdf
- www.sepa.org.uk/waste/information__resources/idoc.ashx?docid=10558a4f-2d53-4301-85d9-b54aa17ff23f&version=-1
Intermediate:
- www.foe.co.uk/resource/briefings/gasification_pyrolysis.pdf
- www.mbt.landfill-site.com/Pyrolysis___Gasification/pyrolysis___gasification.html
Detailed:
- www.defra.gov.uk/environment/waste/research/health.htm
- www.communities.gov.uk/documents/planningandbuilding/pdf/148385.pdf
Incineration
Incineration is the controlled combustion of waste including energy recovery. Heat released from the combustion can be recovered and used to generate electricity, heat, steam or hot water; this process is often known as Energy from Waste (EfW). Incineration can reduce the volume of waste by up to 90% and reduces the hazardousness of waste. It is a common technology in Europe, and there are a number of plants operating in the UK including a small-scale plant in Lerwick, Shetland and a large-scale plant in Dundee. Incineration may be combined with a range of other waste treatment technologies.
Inputs
Incineration can treat a wide range of waste types including Municipal Waste (MW), industrial waste, and Refuse Derived Fuel (RDF). While large-scale plants can treat unsorted waste, small-scale plants are specifically designed to take a relatively homogenous, pre-processed feedstock.
Process
Waste is collected and delivered to the site where it is deposited in a bunker and mixed to ensure a more consistent and even calorific mix. It is then fed into a furnace where it is burned. Small-scale plants may require an initial injection of auxiliary fuel to start up. There are a number of different furnace designs: the furnace may use oscillation, rotation, or a grate system to ensure a more even burn, or may use fluidised beds to create turbulence in order to maximise combustion of waste. The unburned residue, known as bottom ash, is stabilised and is deposited into a tank. Magnets remove any ferrous metals from the ash for recycling, and the remaining ash can be recycled for use in construction. The hot gasses produced during combustion are then directed to a boiler where electricity can be generated and heat recovered. Gases are thoroughly cleaned using a range of emission control systems before they are emitted to the atmosphere. Filtered particles are collected and sent to special waste landfill. Under the Waste Incineration (Scotland) Regulations 2003 all emissions are continuously monitored.
Outputs
1 tonne of MW produces approximately:- 30-60kg of hazardous waste for landfill;
- 200-300kg of bottom ash for landfill;
- 30-50kg of metals extracted from bottom ash for recycling;
- waste water for treatment via a sewage treatment plant;
- Electricity and Heat: approximately 2,000 kilowatt hours of heat per tonne of waste can be recovered, of which 90% is available for export once a certain fraction has been used for running the plant; and
- Emissions.
Regulation- EU Landfill Directive (99/31/EC) requires a reduction in the amount of BMW to landfill. The Directive also requires Member States to set up a national strategy for the implementation of these targets.
- Integrated Pollution Prevention and Control Directive (96/61/EC) was created to prevent or minimise emissions to air, water and soil, as well as waste.
- Waste Incineration (Scotland) Regulations (SSI 2003/170) introduced strict regulatory controls, whereby all emissions are constantly monitored, and minimum technical requirements for waste incinerators have been established.
- Public Participation Directive (2003/35/EC) requires that the application and decision document for a waste treatment installation permit must be made available to the public for their comment.
- Animal By-Products Regulation (Scotland) (SSI 2003/411) establishes health rules concerning animal by-products not intended for human consumption and applies to food waste that is composted.
Further Information
Introductory:
- www.defra.gov.uk/environment/waste/wip/newtech/pdf/incineration.pdf
- www.sepa.org.uk/waste/information__resources/idoc.ashx?docid=8ce6602b-e3a0-4e85-a6dd-ec54496f2b3b&version=-1
Detailed:
In-Vessel Composting
In-Vessel Composting (IVC) is a managed process in which biodegradable waste is broken down by naturally occurring micro-organisms with oxygen to produce a stabilised residue known as compost. There are several IVC plants in the UK including one in Lanarkshire, two in Aberdeenshire, one in Fife, three in Argyll & Bute, and one under construction in Highland.
IVC can be combined with a range of other waste treatment technologies. It can be used after waste has been treated at a Materials Recovery/Recycling Facility (MRF) and in conjunction with waste treatment technologies for the non-organic fraction of waste.
Inputs
Biodegradable municipal waste (BMW), agricultural waste and food processing wastes. Food wastes may be treated only if the plant is compliant with Animal By-Products (Scotland) (SSI 2003/411). Ideally this process should treat only segregated biodegradable waste. Mixed waste can be treated by anaerobic digestion; however this may result in contamination of the liquid and solid fractions which can make them less suitable as soil conditioners or fertilisers.
Process
Waste is collected and brought to the site where it is initially sorted to remove any non-biodegradable waste and shredded to a consistent size. It is then put into a closed reactor where the composting process is speeded up through the management of water, air and heat. This process typically takes between 7 and 21 days. The material is then subject to another screening to remove any traces of metals, and goes through a further maturation period of up to 10 weeks. It can then be used as compost or soil conditioner.
Outputs
1 tonne of MW produces approximately:- 200-300kg of emissions (mainly water vapour and carbon dioxide (CO2));
- 500kg-600kg of compost;
- 50-300kg remainder to landfill (depending on contamination level of waste); and
- 200kg of wastewater which can be treated or reused on site or treated at a sewage treatment works.
Regulation
- EU Landfill Directive (99/31/EC) requires a reduction in the amount of BMW to landfill.
- Integrated Pollution Prevention and Control Directive (96/61/EC) was created to prevent or minimise emissions to air, water and soil, as well as waste.
- European Standards, PAS100 and EU Class-1 compost quality control standards.
- Public Participation Directive (2003/35/EC) requires that the application and decision document for a waste treatment installation permit must be made available to the public for their comment.
- Animal By-Products Regulation (Scotland) (SSI 2003/411) establishes health rules concerning animal by-products not intended for human consumption and applies to food waste that is composted.
Further Information
Introductory:
Intermediate:
Detailed:
Landfill
Landfill is the disposal of waste into or onto land. Today, landfill sites are constructed and operated to strict technical standards in order to reduce environmental effects. In 2005 there were 190 landfill sites in operation in Scotland.
Inputs
Most types of waste may be disposed of via landfill; however the EU Landfill Directive 1999/31/EC requires that Landfill sites must now be classified as either hazardous, non-hazardous, or inert. Reducing the amount of waste to landfill is currently being encouraged by the Landfill Directive to recover value from waste and develop more sustainable waste management.
Process
When waste is received it is weighed and checked to ensure it is compliant with its landfill operating licence. It is then tipped into the landfill, compacted and covered to prevent odour, litter, and pest infestations. The waste will then be gradually decomposed by microbes. This decomposition process, mixed with rainwater creates leachates and gas, which are both taken out of the landfill through a system of pipes. The leachates are then usually taken for treatment, while the gas, mainly a mix of carbon dioxide and methane, may be burnt off or used in an on-site energy generation plant which contributes energy to the national grid. When landfill has reached maximum capacity it is covered completely with an engineered cap, e.g. using clay and restored using soils or other covering materials so that the sites can be used for agriculture, amenities or nature conservation.
Outputs- Landfill Gas (primarily methane (CH4) and carbon dioxide (CO2), which may be burned for energy.
- Leachates (a liquor resulting from water passing through the waste mass).
Regulation
- EU Landfill Directive (99/31/EC) requires a reduction in the amount of BMW to landfill, the segregation of hazardous and non-hazardous waste, and pre-treatment of waste prior to landfill.
- Scotland's National Waste Plan aims to reduce MW to landfill from 90% to 30% by 2020.
Further Information
Intermediate:
Introductory:Detailed:
Materials Recovery / Recycling Facilities
Materials Recovery/Recycling Facilities (MRFs) are locations where waste undergoes treatment to be separated and sorted mechanically and/or manually. There are a number of MRF sites in Scotland including one in Aberdeen and one in Grangemouth. MRFs can be used as a preliminary waste treatment process and combined with a range of other waste treatment technologies.
Inputs
The waste input depends upon the type of MRF facility. "Clean" MRF facilities processes dry recyclables only, while "dirty" MRF facilities can process mixed municipal waste and some industrial waste. Dirty MRF is also associated with Mechanical Biological Treatment MBT, due to the possible similarities in the way in which dirty MRF and MBT separate mixed waste. MRF facilities in the UK tend to be clean MRF facilities, and it is unlikely that dirty MRF facilities will be introduced.
Process
Waste is deposited at the plant where it is then separated through a system of conveyer belts, screening and other sorting systems. The type of separation process utilised depends largely on both input and after use of the separated materials. After the materials have been sorted they can then be bulked and then transported for further processing.
Outputs
Depending on input, for every 1 tonne of waste there is approximately:- 400-970kg of recyclable material. Dirty MRF will typically recover 100-150kg of material that is recyclable;
- 250-400kg of material for biological treatment usually by composting or anaerobic digestion. Organic outputs from a dirty MRF will usually be contaminated and of limited value; and
- 30-710kg waste to landfill.
Regulation- EU Landfill Directive (99/31/EC) requires a reduction in the amount of BMW to landfill.
- Integrated Pollution Prevention and Control Directive (96/61/EC) was created to prevent or minimise emissions to air, water and soil, as well as waste.
- Public Participation Directive (2003/35/EC) requires that the application and decision document for a waste treatment installation permit must be made available to the public for their comment.
Further Information
Intermediate:
- www.sepa.org.uk/waste/information__resources/idoc.ashx?docid=fa8d8a03-589e-4517-9c41-814d4cccd0fe&version=-1
- www.mbt.landfill-site.com/Dirty_MRF/dirty_mrf.html
- www.mbt.landfill-site.com/MRF/mrf.html
Detailed:
- www.defra.gov.uk/environment/waste/research/health.htmm
- www.communities.gov.uk/documents/planningandbuilding/pdf/148385.pdf
Mechanical / Biological Treatment
Mechanical/Biological Treatment (MBT) is a hybrid treatment which combines biological and mechanical techniques, and may also use techniques to produce Refuse Derived Fuel (RDF). MBT can reduce the volume of waste to landfill by around 20% depending on the input, improves the quality of recyclable materials, and stabilises waste. There are over 70 MBT plants working in Europe, and there are a number of MBT plants operating in the UK including three in Argyll and Bute. MBT may be combined with a range of other waste treatment technologies.
Inputs
Unsorted Municipal Waste and non-hazardous waste. MBT is sometimes referred to as "dirty MRF" as it processes mixed household waste. This is in contrast to "clean MRF" which is associated with processing of dry recyclables.
Process
The MBT process and outputs depends greatly upon the needs of the recipients of the outputs and the availability and access to markets for the outputs. However, the process generally follows one of two routes. Waste is collected and brought to the site where it can then be treated mechanically then biologically, or biologically then mechanically. Waste is treated mechanically in order to reduce its volume and separate it into different waste types. The biodegradable fraction of the waste is treated in a managed biological process in which it is broken down by naturally occurring micro-organisms. The organic output may have a higher level of contaminants (for example plastics and glass) than other biological treatment processes which only treat BMW, such as Open Windrow Composting or Anaerobic Digestion.
Outputs
1 tonne of MW produces approximately:- 250kg Water Vapour & CO2;
- 35-345kg recyclable materials;
- 500kg organic output - use as compost is dependent on quality of the material. This material may also be used to make refuse derived fuel (RDF);
- 100-200kg of residual waste to landfill;
- Wastewater.
Regulation- EU Landfill Directive (99/31/EC) requires a reduction in the amount of BMW to landfill.
- Integrated Pollution Prevention and Control Directive (96/61/EC) was created to prevent or minimise emissions to air, water and soil, as well as waste.
- Public Participation Directive (2003/35/EC) requires that the application and decision document for a waste treatment installation permit must be made available to the public for their comment.
- Animal By-Products Regulation (Scotland) (SSI 2003/411) establishes health rules concerning animal by-products not intended for human consumption and applies to food waste that is composted.
Further Information
Introductory:- www.sepa.org.uk/waste/information__resources/idoc.ashx?docid=5ce2480f-3964-46e7-af52-23a3fe43b1d9&version=-1
- www.defra.gov.uk/environment/waste/wip/newtech/pdf/mbt.pdf
Intermediate:
Detailed:Mechanical / Heat Treatment
Mechanical/Heat treatment (MHT), including techniques such as autoclaving, is a treatment process which incorporates heat using steam (either wet or dry) with or without pressure, alongside a number of separation techniques. MHT reduces the volume of waste by 60/70%, stabilises waste and produces material suitable for energy generation. MHT is a relatively new technology for the treatment of Municipal Waste, though there are a number of demonstration plants operating in the UK. MHT can be combined with a range of other waste treatment technologies.
Inputs
Unsorted or separated Municipal Waste, commercial waste, clinical waste, animal by-products and certain industrial wastes.
Process
Waste is collected and brought to the site where it is placed in a pressurised container called an autoclave and then "cooked" using steam for about 90 minutes at a temperature of 160oC. The process is effective in killing off viruses and pathogens and transforming the physical characteristics of the waste. The waste is then easily separable into recyclates, Refuse Derived Fuel (RDF) and organic fibre. After separation glass, metals and plastics are cleaned and can then be sent on for further treatment. RDF can be used for energy generation. The organic fibre requires further treatment for use as compost.Outputs
- Organic fibre, which can be blended and used as a soil conditioner
- Recyclable materials
- RDF may also be produced from the organic fibre and residual waste
Regulation- EU Landfill Directive (99/31/EC) requires a reduction in the amount of BMW to landfill.
- Integrated Pollution Prevention and Control Directive (96/61/EC) was created to prevent or minimise emissions to air, water and soil, as well as waste.
- Public Participation Directive (2003/35/EC) requires that the application and decision document for a waste treatment installation permit must be made available to the public for their comment.
- Animal By-Products Regulation (Scotland) (SSI 2003/411) establishes health rules concerning animal by-products not intended for human consumption and applies to food waste that is composted.
- Waste Incineration (Scotland) Regulations (SSI 2003 No170) introduced strict regulatory controls and set minimum technical requirements for waste incinerators.
Detailed:Open Window Composting
Open Window Composting (OWC) is a managed biological process in which biodegradable waste is broken down by naturally occurring micro-organisms to produce a stabilised residue. There are currently a number of OWCs operating in Scotland, including one at Deerdykes in Cumbernauld.OWC can be combined with a range of other waste treatment technologies. It can be used after waste has been treated at an MRF separation facility, and in conjunction with waste treatment technologies for the non-organic fraction of waste.
Inputs
Biodegradable Municipal Waste (BMW). Only meat excluded food wastes can be treated, as stipulated by the Animal By-Products (Scotland) (SSI 2003/411) Regulations. Ideally this process should treat only segregated biodegradable waste. Mixed waste can be treated by anaerobic digestion; however this may result in contamination of the liquid and solid fractions which can make them less suitable as soil conditioners or fertilisers.
Process
Waste is collected and brought to the site where it is checked to ensure it is of sufficient quality. It is then shredded and piled into windrows, which are elongated piles shaped for ideal composting. Aeration is encouraged by suitable mixing of the initial material and regular mechanical agitation (turning). Decomposition is allowed to continue until the waste has been stabilised and matured. Before use, the compost is checked for contaminants to ensure that it fulfils the physical, chemical and biological requirements for commercial compost.
Outputs
1 tonne of BMW will produce approximately:- 200-300kg of gas emissions including CO2, Water vapour and methane;
- 500-750kg of compost - use dependent on quality of the material; and
- 50-300kg of residual waste to landfill.
Regulation
- EU Landfill Directive (99/31/EC) requires a reduction in the amount of BMW to landfill.
- Integrated Pollution Prevention and Control Directive (96/61/EC) was created to prevent or minimise emissions to air, water and soil, as well as waste.
- Public Participation Directive (2003/35/EC) requires that the application and decision document for a waste treatment installation permit must be made available to the public for their comment.
- Animal By-Products Regulation (Scotland) (SSI 2003/411) establishes health rules concerning animal by-products not intended for human consumption and applies to food waste that is composted.
Further Information
Introductory:
Intermediate:
- www.sepa.org.uk/waste/information__resources/idoc.ashx?docid=6fffd406-4668-44f4-9a6a-3e8f6822a30d&version=-1
- www.mbt.landfill-site.com/Composting/composting.html
- www.defra.gov.uk/environment/waste/wip/newtech/pdf/abt.pdf
Detailed:
Pyrolysis
Pyrolysis is the controlled combustion of waste in the complete or partial absence of oxygen at temperatures between 400ºC and 800ºC. It reduces the volume of waste by approximately 90%, and produces gas for energy generation. Pyrolysis is a relatively new technology for the treatment of Municipal Waste (MW). There are currently no pyrolysis plants treating MW in Scotland; however there is a fully operational (but not full scale) demonstration plant in Bristol that combines both Gasification and Pyrolysis. Pyrolysis can be combined with a range of other waste treatment technologies.
Inputs
Pyrolysis can treat MW and other waste types including commercial and industrial waste, and clinical waste.
Process
Waste is collected and delivered to the site where it is pre-treated to remove non-combustibles such as glass and metal, remove excess moisture, and sometimes shredded to a uniform size. It is then fed into the pyrolysis reactor where it is burnt, or "pyrolysed". The unburned residue, or char, from the non-organic fraction of MW is stabilised and is deposited into a quench tank. Magnets remove any ferrous metals from the ash for recycling and the remaining ash may be recycled for use in construction. The combustion process also produces carbon which is transformed into syngas. This can be refined, using a system of scrubbers and cleaners in order to remove tar, sulphur compounds and other acid gases, which are then sent to landfill. This produces a highly efficient gas for combustion on-site or transported to other energy generation sites.
Outputs
1 tonne of BMW will produce approximately:- 200-300kg of char for use in construction or landfill;
- 20kg of hazardous waste for landfill; and
- Syngas. This provides a high efficiency energy generation in comparison with other heat treatment facilities, due to the degree of refinement of the syngas.
Regulation- EU Landfill Directive (99/31/EC) requires a reduction in the amount of BMW to landfill.
- Integrated Pollution Prevention and Control Directive (96/61/EC) was created to prevent or minimise emissions to air, water and soil, as well as waste.
- Public Participation Directive (2003/35/EC) requires that the application and decision document for a waste treatment installation permit must be made available to the public for their comment.
- Animal By-Products Regulation (Scotland) (SSI 2003/411) establishes health rules concerning animal by-products not intended for human consumption and applies to food waste that is composted.
- Waste Incineration (Scotland) Regulations (SSI 2003 No170) introduced strict regulatory controls and set minimum technical requirements for waste incinerators.
Further Information
Introductory:
Intermediate:- www.mbt.landfill-site.com/Pyrolysis___Gasification/pyrolysis___gasification.html
- www.sepa.org.uk/waste/information__resources/idoc.ashx?docid=f80709d3-d85b-4354-874a-81f6632111b1&version=-1
Detailed:
- www.communities.gov.uk/documents/planningandbuilding/pdf/148385.pdf
- www.defra.gov.uk/environment/waste/research/health.htm
