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Dirty MRF
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Unsorted / residual waste Materials Recovery Facility (Dirty MRF)

Dirty Materials Recovery Facilities are housed facilities which combine a number of screening / sorting techniques to divide residual municipal waste into a recyclable material stream and a non-recyclable residual waste stream disposed to landfill. More advanced plant (as shown in the diagram below) may be used to produce a third stream either a primarily biodegradable waste stream which can be sent for Anaerobic Digestion or In-vessel composting or a relatively high calorific value stream for conversion to Refuse Derived Fuel.

The facilities employ conveyor systems, bag splitters, screens or trommels to split the waste into different size fractions and magnets, eddy current separators, handpicking or other sorting techniques such as air classifiers to divide the waste stream into the required constituent streams. The process will not produce recyclate of the same quality as a clean MRF due to contamination from putrescibles and the less efficient separation process. This will impact on income from recyclate derived from such facilities.

Dirty MRFs will typically recover around 10 – 15% of material as recyclables and the remainder would either require further processing or disposal. It is typical for metals to be extracted through this process and mixed plastics, paper, glass, card and textiles may also be removed for recycling through the operation.

Dirty MRFs have had limited success in the UK, largely due to poor levels of income from recyclate and the volatility of the recycling market. There are currently several operational dirty MRFs in England however there are some facilities still in operation in Scotland and a facilities have recently completed in Neath Port Talbot, Wales, as part of an integrated waste management facility also incorporating RDF and In-vessel composting, and also Cardiff, Wales.

Schematic of Inputs and Outputs of a typical Dirty MRF process

Image of the Dirty MRF process

Typical capacity: 100,000 – 200,000 tpa

Land requirements: 2 - 4Ha

Capital Costs: (See full report.)

Operating costs: Gate fee for low technology 100ktpa plant - (See full report.)

Staffing requirements: Staffing levels, including technical competence, management and administrative resources will vary depending on the size and technology adopted. A 100ktpa plant had 24 staff.

Strengths & Weaknesses of Dirty MRFs

Strengths

Weaknesses

Extracts additional recyclables from residual waste stream

Low quality of recyclables output can render material of low value.

Generally lower capital costs compared to clean MRFs (per tonne equivalent)

Unless there is a high level of separation in the plant, there is likely to be a major component of the waste entering the plant going to a disposal facility (landfill or energy from waste).

Can be used as part of an integrated system to gain energy and materials value out of the residual waste stream

Where materials are divided for example into biodegradable and combustible material streams, the facility is reliant on the availability of other waste management operations.

Lower cost than MBT whilst achieving similar aims (although potentially less effectively)

Potential dust / odour problems and health issues for staff on picking belts

Applying proven technology

Any biodegradable stream derived from plant will be subject to the Animal By-products legislation

 

Outputs from the plant will still be classified as BMW under the Landfill Directive and active waste under Landfill Tax

Other Issues:

The Dirty MRF is similar in many ways to some Mechanical Biological Treatment (MBT) processes, with the exception of the biological component. More complex Dirty MRF systems can split the waste stream into three streams in a similar manner to MBT, however as the waste is usually still wet during the dirty MRF operation separation and extraction of materials is commonly less efficient. There is also no mass reduction through the Dirty MRF process unless other pre-treatment operations are used (see 'Other Pre-treatment Options' section).

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