MBT Process

MBT is commonly used to treat municipal solid waste (MSW), it is capable of dealing with both mixed waste and source separated waste.The mechanical part which is the physical stage of an MBT process is normally at the front end of the process although it can also play a key role at the back end of the process. The MBT plant can be designed to have further mechanical screening at the end of the process to take out further contaminants and or reduce particle size, especially if the residues are going to be used for a purpose other than landfill Mechanical separation process can include size reduction/shredding of the waste, separation of ferrous and non-ferrous metals, heat/steam treatment and screening and/or size reduction of outputs.

Not all of the above are used in each MBT facility. For example if the aim is to maximise recovery and recycling and to stabilise the residue further that will be sent to landfill, a mechanical process which recovers dry recyclables (card, plastics, paper and metals) would be ideal. The mechanical process can be both a dry and wet process depending on the role of the final product. The aim of the mechanical process is that the remaining waste, after the mechanical separation, is the organic-rich fraction or biodegradable fraction which will be ideal for biological treatment.
 
The biological processes of MBT include aerobic decomposition to anaerobic digestion (AD), or a combination of the two. If AD is used to digest the organic-rich waste fraction biogas is often produced which can then be used as a source of energy. MBT is also often used to produce a soil conditioner and/or refuse derived fuel (RDF). The amount and quality of biogas, soil conditioner and RDF produced depends on the particular facilities composition (Juniper). Anaerobic or aerobic composting of mixed MSW will not produce a material of appropriate quality without some form of mechanical treatment at the front end of the MBT plant.
 
The MBT process is quite complex with a number of variables giving considerable flexibility. MBT systems can be a modular design which means they can be switched from processing mixed MSW to processing source separated organic waste, which may need to occur if the collection system is changed from a mixed waste collection system to a source segregated collection. Sites processing both mixed/residual MSW and to an increasing extent separately collected biowaste are often known as “double duty” sites, these sites, are quite diffused across Europe, and may provide a flexible answer to the need to tackle changes in schemes and of local strategy.