Mechanical biological treatment
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"MBT" redirects here. For other uses, see MBT (disambiguation).
Mechanical biological treatment ("MBT"), or "mechanical biological pre-treatment" is a category of waste treatment technologies that enables recovery of the resources contained in waste.[1] [2]
The resources, including metals, plastics and glass can then be recycled. It consists of any number of combinations of mechanical sorting and biological treatment processes for mixed waste streams. MBT generally, but not exclusively is used to process unsorted household waste.
MBT is also sometimes termed BMT – biological mechanical treatment – however this simply refers to the order of processing. MBT should not be confused with MHT – mechanical heat treatment.
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[edit] Mechanical factor
- See also: Materials recovery facility
The "mechanical" element is usually an automated mechanical sorting stage. This either removes recyclable elements from a mixed waste stream (such as metals, plastics and glass) or processes them. It typically involves factory style conveyors, industrial magnets, eddy current separators, trommels, shredders and other tailor made systems. The mechanical element has a number of similarities to a materials recovery facility (MRF).[3]
Some systems integrate a wet MRF to recover & wash the recyclable elements of the waste in a form that can be sent for recycling. MBT can alternatively process the waste to produce a high calorific fuel given the term refuse derived fuel (RDF). RDF can be used in cement kilns or power plants and is generally made up from plastics and biodegradable organic waste. Systems which are configured to produce RDF include the Herhof and Ecodeco Processes. It is a common misconception that all MBT processes produce RDF. This is not the case and depends strictly on system configuration and suitable local markets for MBT outputs.
[edit] Biological factor
- See also: composting and anaerobic digestion
The "biological" element refers to either:
- Anaerobic digestion
- Composting
Anaerobic digestion breaks down the biodegradable component of the waste to produce biogas and soil improver. The biogas can be used to generate renewable energy. Some processes through water based processing enable high rates of gas and green energy generation without the production of RDF. This is facilitated by processing the waste in water.
Biological can also refer to a composting stage. Here the organic component is treated with aerobic microorganisms. They break down the waste into carbon dioxide and compost. There is no green energy produced by systems employing only composting treatment for the biodegradable waste.
Some systems, such as UR-3R involve both a partial anaerobic digestion stage along with a secondary composting stage.
By processing the biodegradable waste either by anaerobic digestion or by composting MBT technologies help to reduce the contribution of greenhouse gases to global warming.
[edit] Implications on kerbside collection
The more advanced MBT solutions offer the ability to reduce the need for home separation and kerbside collection of recyclable elements of waste. This gives the ability of local authorities and councils to reduce the amount of waste vehicles on the roads and keep recycling rates high.
This goes against some environmental thinking which pushes for people to recycle in the home so they are more aware and take ownership of the waste they produce.
MBT is gaining increased recognition in countries with changing waste management markets such as the UK.
[edit] Friends of the Earth position
Friends of the Earth suggests that the best environmental route for residual waste is to firstly remove the remaining recyclable elements from the waste stream (such as metals, plastics and some paper). The small amount of waste remaining should be composted or anaerobically digested and unless sufficiently clean to be used as a compost should be disposed of in landfill. MBT plants that fit in with these statements could therefore play an increasing role in the environmental management of mixed streams. [4]
[edit] Process examples
[edit] ArrowBio
Water-based MBT; ArrowBio, is a variant technology that comes under the general category of mechanical biological treatment, however is distinct in its application of water.[5] The system combines mechanical sorting (in a water based materials recovery facility with water based UASB anaerobic digestion.[6]
The system washes and extracts the recyclable elements of the unsorted bin bags recovering resources such as metals, plastics and glass. This process does not produce RDF and does not require its outputs to be burnt. The technology produces green energy from biogas and clean soil improver. A "hydrocrushing" stage results in significantly more of the biodegradable material being converted into biogas.[7]
A commercially operating reference facility is based at the Hiriya waste park. A second system is under construction at the Jack's Gulley landfill and will be operated by WSN Environmental Solutions.
Process inputs:
- Mixed municipal solid waste (or similar biodegradable waste stream)
Process outputs:
- Cleaned recyclables: Ferrous metal, non-ferrous metals, HDPE, PET, LDPE
- Biogas (converted into renewable energy)
- Soil improver (digestates from anaerobic digestion)
- A residue of non-recoverable elements which is sent to landfill (c20% of input)
- Cleaned water recirculated in system and exported
[edit] See also
- Anaerobic digestion
- Composting
- List of solid waste treatment technologies
- Materials recovery facility
- Renewable energy
- Waste
- Waste management
[edit] External links
- Example of a water-based MBT process
- Environment Agency Waste Technology Data Centre An independent UK government review of advanced waste treatment technologies.
- Enviros Mechanical Biological Treatment Information Page
- Juniper MBT report An independent study of MBT technologies commissioned with the use of UK landfill tax credits.
- SEPA MBT Planning Information Sheet Fact Sheet for Scottish Planning Considerations
[edit] References
- ^ Enviros (2006) Mechanical biological treatment website, www.mbt.landfill-site.com, Waste Technology Home Page, Accessed 22.11.06
- ^ Juniper (2005) MBT: A Guide for Decision Makers – Processes, Policies & Markets, www.juniper.co.uk, (Project funding supplied by Sita Environmental Trust), Accessed 22.11.06
- ^ Sita (2004) Sita Mechanical Biological Treatment Position Paper, www.sita.co.uk, Accessed 22.11.06
- ^ Friends of the Earth (2005)MBT & FOE, www.foe.co.uk, Mechanical Biological Treatment Briefing, Friends of the Earth, Accessed 22.11.06
- ^ Finstein, M. S., Zadik, Y., Marshall, A. T. & Brody, D. (2004) The ArrowBio Process for Mixed Municipal Solid Waste – Responses to “Requests for Information”, Proceedings for Biodegradable and Residual Waste Management, Proceedings. (Eds. E. K. Papadimitriou & E. I. Stentiford), Technology and Service Providers Forum, p. 407-413, www.alexmarshall.me.uk, Accessed 22.11.06
- ^ Environment Agency (2005)Report on ArrowBio, www.environment-agency.gov.uk, Environment Agency Waste Technology Data Centre, Accessed 22.11.06
- ^ Defra (2005) Defra MBT Publication, www.defra.gov.uk, Mechanical Biological Treatment and Mechanical Heat Treatment of Municipal Solid Waste, Defra Waste Implimentation Programme, New Technologies, Accessed 22.11.06
| Energy Conversion Edit | |
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| Solar power: | Active solar | Barra system | Energy Tower | Photovoltaics | Solar cell | Solar panel | Solar pond | Solar power tower | Solar thermal energy | Solar tracker | Solar updraft tower | Passive solar | Trombe wall | Ocean thermal energy conversion |
| Wind power: | Wind farm | Wind turbine |
| Hydroelectricity: | Marine current power | Tidal power | Water turbine | Wave power |
| Biological: | Mechanical biological treatment | Anaerobic digestion | Biomass |
| Chemical: | Blue energy | Fuel cell | Hydrogen production |
| Geothermal power: | Earth cooling tubes | Deep lake water cooling |
| Electricity generation: | Distributed generation | Microgeneration | Sustainable community energy system | Seasonal thermal store |
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