Mechanical & Biological Waste Treatment

An addition to the site in 2009 was the construction of a Mechanical Biological Treatment / Bio-Drying Plant used to process Household waste. This aids the recovery of recyclables as well as reducing the production of methane gas and its effect as a greenhouse gas, from the residual waste which is sent to landfill.

Mechanical and Biological Treatment covers a variety of technologies that pre-treat residual black bag municipal waste. The systems tend to fall into two categories, with the main difference being the stage at which the biological part of the waste is treated – whether before mechanical separation of the waste (MBT) or after (biological mechanical treatment –BMT), the plant built at Aycliffe Quarry by a Dutch company, Gicom, adopts the 2nd principle; In simple terms biologically drying the waste.

The Household Waste (MSW) is delivered in black sacks which are ripped open to gain access to the waste; the aim is not to shred the waste but to allow a can to remain a can etc. The waste can now be processed in enclosed tunnels to allow natural organisms, (such as can be found in your garden composter) assisted by the controlled air, water and temperature to aid the breakdown of the waste. The waste is first pasteurised at 60+ degrees for 30 hours then reduced to a conditioning temperature of around 45 – 50 degrees for a further 10 to 12 days, the heat generated in the process is used to dry the waste.

On completion the treated waste is taken for sorting using a series of trommel and inclined screens, air blowers, magnetic separation and eddy current separation. Any materials that have added value as recyclables are separated from the dried waste and are added to the source segregated material received from the Kerbside collection rounds. The remainder of the waste continues along the sorting line to a High Speed Shredder where it is reduced to a 30-40mm size.

3 weeks after been collected from the streets, the final material is known as SRF (Solid Recovered Fuel) and is used as a high calorific fuel in the production of cement. The Plant is capable of handling 50,000 tonnes of MSW; it currently receives around 25 to 30,000 tonnes from Darlington Borough Council as part of a contract taking us up to 2025.

The treatment process works in conjunction with the “Bag It, Box It, Bin It” regime operated by Darlington Council, by which paper and cardboard goes into a caddy, glass goes into a box, tins and plastic into a recycling bin and everything else goes into the bin (Black Bag).

The combination of the collection systems and the subsequent treatment processes means that very little of the waste collected from Darlington now ends up in landfill.
For more information please visit the Darlington Council Website here.

John Wade Composting After Processing

The 2nd Part of the Plant processes Green Waste to make PAS100 Compost; this is once again sold on as a Product.

The compost has numerous uses as well horticultural and can also be used in agriculture as a replacement to granular fertilizers with added benefits as a soil improver. The site currently receives around 500 tonnes per week of green waste during the summer and this produces around 350-400 of compost. Similar to the MSW the green waste is shredded, placed into the Bunkers for 12-14 days, taken out to be re-shredded and screened into smaller sizes before going back into the Bunkers for a further 5 days. The oversized material is being used as biomass to produce energy in the form of heat and electricity.

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