Mechanical Biological Treatment

• Mechanical Biological Treatment (MBT) is a generic term for an integration of several processes commonly found in other waste management processes such as Materials Recovery Facilities (MRFs), Refuse Derived Fuel (RDF), sorting and composting plant.
• At present MBT facilities are currently under development in the UK. The facilities are usually housed and kept under negative pressure with biofilters to help address any odour / emissions to air.

There are a wide variety of systems promoted to the UK municipal waste management market. The principle of the MBT plant is to stabilise and separate the residual waste stream (what is left after recyclate is removed) into less harmful and / or more beneficial output streams. The processes are designed to handle raw 'black bag' municipal waste (after any source segregated recycling and composting has taken place) and tends to involve a recyclate recovery element (typically metals and glass) and a drying / partial composting of the remaining waste to produce a more stabilised residue.

The recyclable component may be extracted either prior to or post 'stabilisation'. The remainder of the waste is screened / sorted and homogenised to produce either a feedstock for another treatment process (e.g. a refuse derived fuel for energy recovery in a gasification, co-incineration, or Energy from Waste plant) or may be sent to landfill as a partially stabilised residue.

Some systems may screen the waste to produce a compostable stream appropriate for in-vessel composting processes. Where the waste is to be used, as a secondary fuel there is usually a minor non-combustible element sent for disposal to landfill. An alternative MBT approach is the extraction of recyclables followed by homogenisation of the residue prior to processing in an Anaerobic Digestion plant. Whole waste composting with some materials extraction may also be regarded as simple MBT to provide a residue for landfilling / low grade land restoration type applications / subsequent thermal treatment

Key issues with regard to Mechanical Biological Treatment include the impacts of legislation upon the products of the process. The output of an MBT process will be classified as biodegradable under the EU Landfill Diversion Targets, unless additional processing takes place such as composting.

The composting of the output would be subject to the Animal By-products Regulations (ABPR).

Other treatment processes  (for example co-incineration of the fuel in cement kilns, or power stations) will incur a gate fee, which is currently subject to market testing in the UK.

Some systems may include facilities to screen the waste to produce a minor compostable stream appropriate for in-vessel composting processes.

Where the waste is to be used as a secondary fuel there is usually a minor non-combustible element which remains after processing, which is sent for disposal to landfill.

An alternative MBT approach is the initial extraction of recyclables, followed by homogenisation of the residue prior to processing in an Anaerobic Digestion (AD) plant.

Whole waste composting with some materials extraction may also be regarded as simple MBT to provide a residue for landfilling / thermal treatment.

All facilities are usually housed and kept under negative pressure for the avoidance of odour nuisance.

(source: www.mbt.landfill-site.com).