MBT or Mechanical Biological Treatment is a large scale process which involves two main treatments:
- Mechanical – Involves shredding, screening and metal extraction. These processes result in the separation of oversized, inert, recyclables and biodegradable waste fractions.
- Biological – Biodegradable fraction is broken down by microbial activity within a controlled environment
MBT treatments fall into two general types of processes:
- Splitting Process. This is mechanical separation prior to biological treatment, which separates out the residual waste into recyclable and biodegradable fractions. Typically this process would involve shredding the residual waste, followed by magnetic extraction of ferrous metal and then screening into two sizes. Large size fraction then goes to incineration or landfill, and the small waste fraction (100mm-150mm) can be composted or biodigested. Further screening of contaminants such as plastics is normally required.
- Dry Stabilisation Process. This is Biological treatment prior to mechanical separation, where the entire mixed waste is composted in an enclosed air-controlled plant. Materials separation takes place after the composting, and the stabilised biodegradable fraction of about 10% can be used as landfill cover. The remainder of the stabilised waste is converted to RDF (Refuse Derived Fuel).
What you should look out for with MBT
MBT deals with mixed waste with no obligation on householders to source separate their waste. This is convenient at first sight, but detaches the public from direct involvement in re-cycling or responsibility for their own waste. This in turn removes public pressure on manufacturers and retailers to reduce packaging and may lead to the continuation of current large increases in waste per household.
Non Source-separated biodegradable waste from MBT cannot be classed as high quality compost, and therefore is very unlikely to be of sufficient quality for agricultural or horticultural use, making it into another waste stream instead of a useful bio-fertiliser.
Source separated biowaste becomes a valuable source of hygienic bio-fertiliser, and if processed through Biodigestion, a source of Renewable Energy.
What seems like an easy overall solution can, in the long term, prove very costly.