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A recent addition is 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.
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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 through 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, at which point the waste is then dried.
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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.
This maximizes the diversion of recyclable materials e.g. yogurt pots, margarine tubs, other plastic containers/bottles, carrier bags, metals and some paper/cardboard. What is left is a small amount of mainly inorganic fine fraction which is used for engineering cover within the landfill site (but without the ability to produce methane), and an oversize fraction which may have no recycling value but can be used to produce energy from waste (Efw).
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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 an 11 year contract. This approach in handling MSW has changed the way by which the Council collects Kerbside Recyclables.
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In summer 2009 we started a “Bag It, Box It, Bin It” regime with Darlington Council, by which paper and cardboard goes into the bag, glass goes into the box and everything else goes into the bin (Black Bag). These are then taken to our Waste Recycling Plant, for Mechanical Biological Treatment, then all recyclable materials, such as metals, plastics, batteries, drinks cans and containers, food tins and milk cartons, will be extracted for recycling.
This maximizes transportation, reducing the carbon footprint and with the use of the plant all potential recyclables are recovered. Volumes being recovered have now increased with no loss of value.
For more information please visit the Darlington Council Website here.
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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.
