Mechanical Biological Treatment

What is MBT?

MBT processes incorporate mechanical sorting and separation of the waste stream to separate the biodegradable materials, which are sent to a biological process, from the non-biodegradable materials. The mechanical process can be configured to further separate the non-biodegradables into clean fractions for recycling. In Juniper’s classification system, MBT is used as the umbrella term for all types of mechanical biological treatment concepts including BMT (Biological Mechanical Treatment) systems. The main distinction between these different MBT concepts is made on the basis of the order of the process steps and the purpose of the biological treatment options, as discussed below.

• MBT concepts split the waste mechanically into recyclables, residues and an organic fraction that will be used for composting or anaerobic digestion. BMT systems differ from MBT systems in that they utilise the core biological technology to dry and sterilise (but not digest) the waste before it is mechanically sorted to remove non-combustible materials from the waste stream. The remaining material can be combusted and so is referred to as RDF (Refuse Derived Fuel), which could be utilised on-site in a dedicated facility or sent off-site to be utilised as a fuel
• The core biological process used in an MBT system can be AD or composting or elements of both technologies (as in some of the newer MBT processes).
• When AD is incorporated into the MBT system, the process is usually configured to optimise biogas production.  However, in some instances the technology has been configured to optimise the production of soil conditioner or biogas and RDF.
• When composting is the core technology in the MBT process for mixed waste streams, no biogas is produced and the technology can be optimised either to produce compost or RDF.

Typical MBT Process Configuration

Typical BMT Process Configuration

Traditional MBT systems were simple (and therefore low-cost) waste treatment facilities which required little automation and consisted of a mechanical sorting system with an adjacent biological treatment facility. Such low-key treatment options often experienced operating problems. With rising environmental standards and higher recycling expectations both parts of the system have now become more sophisticated and are more closely integrated to provide greater reliability and effectiveness. Novel MBT concepts have developed the traditional approach even further and offer new techniques to reduce energy usage, increase value recovery and reduce environmental impacts of the system.

Process Suitability

• Today, there are over 100 plants operating in Europe using some form of mechanical biological treatment on residual wastes. This total includes several composting plants, particularly in Italy , that have been upgraded with mechanical separation front-ends and could therefore be described as ‘Basic’ MBT systems.
• Purpose-built MBT plants, where the mechanical and biological processes are integrated into a single process system, and which incorporate sophisticated environmental control systems, number over 30 in Europe .  
• These plants are located mainly in Austria , France , Germany and Italy with capacities ranging from a few thousand tonnes per annum up to 200,000 Tpa.  They mainly process source segregated residual waste.
• A number of suppliers have built proprietary MBT systems, which have operated on residual waste from MSW on a commercial basis for a sufficient period of time to be classed as ‘fully commercial’ by Juniper.   Other suppliers, with less operational experience are introducing other MBT variants to the market place; while in other cases, operators of dedicated AD plants are responding to demands for heterogeneous waste treatment capacity by upgrading their conventional ‘AD only’ plants with extensive mechanical feed preparation so that more heterogeneous waste streams can be handled.

Juniper's database contains a number of companies which offer mechanical biological processes or waste stabilisation technologies ranging from combined shredding/separation and biological treatment operations to integrated turnkey processes

Download Juniper's free MBT Report - Juniper's major report on MBT* was published in the spring of 2005 and launched at a one-day seminar in London on 22 March that year. It is now available as a free-of-charge downloadable zip file from WasteReports.com, Juniper's publishing service. To download the report, simply click on the download button below. The Executive Summary is included in the zip file or you can view it as a web-page by clicking the link below. You will need Acrobat Reader to view the pdf files contained in the zip file.

Mechanical Biological Treatment - Applicability to Household Waste - Click here to read an article written by Juniper and published in the Warmer Bulletin, September 2002

*Acknowledgement - The production of the MBT report was funded by UK landfill tax credits provided by Sita Environmental Trust (SET) with additional funding from ASSURRE (The Association for the Sustainable Use and Recovery of Resources in Europe ) to each of whom we wish to express our appreciation. We also wish to thank Dr Gev Eduljee of Sita, Dr Peter White of ASSURRE, Stuart Reynolds of Norfolk Environmental Waste Services and Andy Saunders of SET, who formed a Technical Advisory Committee.  Their insight and many helpful comments were invaluable.