Mechanical biological treatment

Mechanical Biological Treatment (MBT) is a category of waste treatment technologies that enables recovery of the resources contrained in waste. These resources 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.

Mechanical element

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 typcially 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).

Some systems such as 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 Herhof and Ecodeco. 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.

Biological element

See also composting and anaerobic digestion

The "biological" element refers to either:

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 such as ArrowBio 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 simply employing composting.

Some systems, such as UR-3R involve both a partial anaerobic digestion stage along with a secondary composting stage.

MBT and 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.

MBT System Examples

ArrowBio: Water-based MBT

ArrowBiois a variant technology that comes under the general category of mechanical biological treatment, however is distinct in its alternative use of water. The system combines mechanical sorting (in a water based materials recovery facility) with water based UASB anaerobic digestion.

The system washes and extracts the recyclable elements of the unsorted bin bags recovering resources such as metals, plastics and glass. ArrowBio does not produce RDF and does not require its outputs to be burnt. The technology produces green energy from biogas and clean soil improver.

External links

ArrowBio UK 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

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