Technologies to handle general mixed waste
What’s it called?
Mechanical Biological Treatment (MBT)
How does it work?
Although there are wide range of MBT solutions available, the process generally involves shredding the unsorted rubbish, and then removing things like metals for recycling, with the leftover waste then being separated into two groups.
The paper, card and plastics are turned into a ‘fuel’, which can be burnt to generate electricity and hot water. We would need to either build a plant to burn this material, or find a company who could use it as a fuel in an industrial process.
The garden and food waste is composted, or allowed to rot in sealed tanks to produce gas that can be burnt as electricity. The compost-like material can then potentially be used for land remediation or spreading on non-agricultural land.
What are the advantages?
Allows additional recyclable material to be taken out from general waste (i.e. from the waste that goes into your black bin).
Has the potential to reduce carbon emissions from waste management by ‘locking’ the carbon into the compost-like material.
What are the disadvantages?
There a large quantities of the ‘fuel’ and compost-like material left over at the end of the MBT process (around 50% of the waste going in), and markets for dealing with this material are uncertain. Failure to find these markets would require this material to be landfilled, resulting in major environmental and financial impacts.
What’s it called?
Energy from Waste (EfW)
How does it work?
General waste is combusted under controlled conditions, and the heat from this process used to generate electricity which can be sold to the National Grid. Hot water from the process could also be used for heating by local businesses or housing. Emissions are cleaned so as to meet strict environmental requirements. The ash resulting from the process is either recycled for use in construction, or landfilled.
What are the advantages?
This is the most tried and tested technology for treating household waste in the UK, and is highly effective in ensuring that landfill reduction targets are met. Energy can also be recovered from the process. Metals are recovered for recycling at the end of the process.
What are the disadvantages?
For some this process is unpopular as it involves burning all of the waste that we don’t recycle. Some people also have concerns about local emissions from EfW, although evidence shows that modern technology and legislation mean that these facilities operate within strict environmental limits.
What’s it called?
Autoclaving
How does it work?
General waste is shredded and steam treated in a pressurised drum. The remaining ‘flock’ like material may then be mechanically separated into recyclable products, a refuse derived fuel and a residue to be landfilled.
What are the advantages?
Allows additional recyclable material to be taken out from general waste (i.e. from the waste that goes into your black bin). Waste is sanitised and recyclables are cleaned.
What are the disadvantages?
As with MBT (see above), Autoclaving produces a material which can be used as a refuse derived fuel. However, the process does nothing to reduce the volume or biodegradability of the waste, and this requires additional processing or disposal in landfill.
What’s it called?
Advanced Thermal Treatment (ATT)
How does it work?
The main forms of Advanced Thermal Treatment are Pyrolysis and Gasification. Waste is subjected to a heat treatment which produces either an oil or a gas which can be used as a fuel or to generate electricity.
What are the advantages?
ATT facilities are generally on a smaller scale, and could potentially be combined more readily with other technologies.
What are the disadvantages?
Advanced Thermal Treatment is unproven in the UK, and there are few examples abroad. It is primarily designed to treat specific waste types. The residue left over from these treatments still needs additional processing or disposal in landfill.