MTS have partnered with Combined Drier Technology (CDT) to use their mineral drier in a trial with Milestone to process gully waste and allow it to be recycled within the industry at lower costs, both economical and environmental. Gully waste taken from Drayton Depot in a contract with Oxfordshire County Council has been stored in dewatering bays initially before being processed in the mineral drier.
MTS and CDT have undertaken significant amounts of R&D on the mineral drier to increase its efficiency and improve processes in order to produce a recyclable material.
Historically, gully waste has been classed as just that: waste. Considering the UK generated 222.2 million tonnes of total waste in 2018, any opportunity to reduce this amount is so important and should be taken. This is why MTS have undertaken this trial to find an alternative route for gully waste, so it does not have to live up to it’s name. The problem with gully waste is that it is very wet material which makes it very difficult to work with. The mineral drier reduces the moisture content of the gully waste from 25-60% down to ~8%. This allows the material to be screened using fine screen meshes into differing sizes.
Another issue that gully waste faces is that labs often record high levels of total petroleum hydrocarbons (TPH) due to the organic content of the material. The standard technique used by labs is gas chromatography which includes background organics in the TPH result. MTS use the QED hydrocarbon analyser to measure TPH which ignores background organics. Regular testing of material throughout the trial has demonstrated that TPH does not make this material hazardous, and levels fall below the inert 500 mg/kg threshold level. MTS have ben working with laboratories to provide lines of evidence approach in order to prove the material can be classed as non-hazardous and conforms to the inert landfill requirements.
As part of this trial, many modifications to the mineral drier have been made, including a change of fuel source to HVO (hydrotreated vegetable oil) which reduces CO2 emissions by up to 90%. This trial has improved the sustainability of gully waste treatment which can now be done on site at Drayton Highways Depot so also reduces transport costs and emissions. The fact that the resultant material is separated by size based on the sieve size of the screeners means that it conforms to multiple grading requirements for material detailed in the Specification for Highway Works. This means that a material that has been classed as ‘waste’ with no further reuse can now be recycled and be used for varying purposes and in multiple highways and engineering projects.
This project is ongoing with MTS Environmental, Combined Drier Technology, Oxfordshire County Council, Milestone and the Environment Agency are working together to identify how Oxfords’ gully waste can be re-used on the highway network.