Mechanical Biological Treatment Facility (MBT)
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Five state-of-the-art Mechanical Biological Treatment (MBT) plants are planned for Greater Manchester and are currently under construction.
The MBT's are located at the following sites:
- Reliance Street, Newton Heath
- Longley Lane, Sharston
- Cobden Street, Salford
- Arkwright Street, Oldham
- Bredbury Parkway, Stockport
So what is MBT?
MBT is the name given to several processes that are used to treat the waste that arrives at the plant. As the name suggests, MBT involves both mechanical and biological methods.
The ‘mechanical’ part refers to the processes that are used for preparing and separating the waste when it arrives at the plant. There are a number of waste preparation techniques, such as shredding and sieving, which are used mainly
to reduce the size of the waste. Further methods, such as screens, separators, and secondary crushing, are then used to separate the waste into ‘fractions’. Under the new contract between Greater Manchester Waste Disposal Authority (GMWDA) and Viridor Laing (Greater Manchester) Ltd (VLGM), five state-of-the-art Mechanical Biological Treatment (MBT) plants are planned for our area.
How will it work in Greater Manchester?
Waste arrives at the plant, where it is tipped into a large reception
hall. It then goes to the mechanical treatment area, where, using some of the processes mentioned above, it is separated into the following fractions:
- Fine or organic - small particles of mainly organic and non- metallic materials
- Light - mainly non-recyclable plastic, paper, card and textiles
- Ferromagnetic metals - segregated for recycling
- Non-ferromagnetic metals - all other metals, also separated for recycling
- Heavy residue - mainly stones and similar materials, to be used as aggregate
The organic fraction gets mixed with water and processed further to recover any more recyclable materials, such as sand or plastic, and to produce a slurry. Light material is incorporated into a High Calorific Value Refuse-Derived Fuel (HCV-RDF) and heavy residue is reused as aggregate.
So where does the biology come in?
The ‘biological’ part of MBT refers to either composting or digesting of the slurry using aerobic bio-drying, aerobic in-vessel composting or anaerobic digestion. Greater Manchester’s MBT plants will use a wet AD process.
What is Anaerobic Digestion?
This is a renewable energy technology that captures gas (methane) from the decomposition of organic materials, such as manure and slurry; sewage sludge and food waste. By harnessing the natural process that occurs when organic matter is broken down by bacteria in a closed vessel (a bit like what happens in your home composter – but on a bigger scale) the biogas produced can be used as an energy source for both heat and power.
In Greater Manchester the slurry passes through a hydrolysis tank after which it remains in Anaerobic Digestion tanks for up to 25 days. The biogas produced goes to the gas accumulator for use in a Combined Heat and Power (CHP) plant. The remaining product then goes through a process known as de-watering and is further dried to produce a material suitable for use as a Low Calorific Value Refuse-Derived Fuel (LCV-RDF).A Combined Heat and Power (CHP) plant at Runcorn, Cheshire will use the HCV-RDF and LCV-RDF to produce electricity and steam, replacing non-renewable sources of energy.
What are the advantages of MBT using wet AD?
- The mass of waste coming into the plant is reduced
- Additional recyclable materials can be extracted
- The technologies are proven
- The calorific value of waste is increased, so it can be used as fuel
- Works well as part of an integrated waste management system
