MBT plant muscles in for maximum extraction

A plant that combines mechanical sorting and in-vessel composting is set to offer a flexible solution for Cambridgeshire's waste needs. Maxine Perella reports

The in-vessel composting hall inside the MBT facility at Waterbeach

The in-vessel composting hall inside the MBT facility at Waterbeach

This summer I had the rare opportunity of sneaking a glimpse of a state-of-the-art MBT plant from the inside, before the machinery gears into action later this year. The facility is part of a 28-year PFI contract between Cambridgeshire County Council and Donarbon, worth £731M in total, and will be accompanied by other major infrastructure including an in-vessel composting system and two waste transfer stations.

But the centrepiece is the £42M hi-tech MBT plant that is nearing completion in Waterbeach, near Cambridge, and is one of the first of its type in the country. It's uniqueness lies in the fact it will separate dry recyclables from mixed household waste before making a compost-like product with the organic-rich remainder, rather than producing a refuse-derived fuel from the plastics and dried organic remainder.

Adaptable set-up
According to Sarah Clover, director of business development at Donarbon, this will allow greater flexibility to extract maximum value from materials according to how markets evolve in the future. "We can change the way our mechanical sorting works to extract different materials in the future. We feel that incineration wouldn't give us the same flexibility," she explains.

Clover believes that the MBT route was the most cost-effective for the council, and will help them meet their LATS targets going forward. It also proved deliverable in a short space of time. "We signed the [PFI] contract in March 2008 and were able to start build work two months after that," she says.

Building work is due to be completed next month, when the plant will start processing up to 190,000tpa of mixed household (black bag) waste - roughly half of all the household waste generated in Cambridgeshire. The remaining 50% will be recycled through existing kerbside and recycling centre collections, which will also continue throughout the PFI contract.

The MBT facility has been scaled to take account of future projected population growth over the duration of the contract. According to Simon Lacey, communications manager for the council, the population of Cambridgeshire will grow by 100,000 by 2021, which will generate around 50,000 extra tonnes of waste per annum.

Initially, the plant will process some 170,000 tonnes of waste, with 40,000 tonnes recovered through recycling and the other 130,000 tonnes composted. Of this, an output of 90,000 tonnes of compost-like product will be generated for potential use in quarry restoration and bio-fuel crop cultivation. The other 40,000 tonnes will be lost through the composting process.

As the plant will be operating slightly under capacity to begin with, Mark Shelton, waste promotions manager at Donarbon, says it may take waste from neighbouring councils until additional tonnage in the region arises through the projected population growth.

The plant itself has been kitted out with equipment from German and Austrian manufacturers - Komptech on the mechanical sorting side, and Kelag on the in-vessel composting front. The site is divided into three main areas - the waste reception hall, which can store a week's worth of household waste, the mechanical sort area, which contains 62 conveyor belts, and most impressive of all, the composting hall which measures 200m x 75m for processing the macerated organic matter that will be laid across the hall at a depth of 3m before being turned and matured for seven weeks.

Scope for outputs
Dry recyclables from the mechanical sorting area will go to existing recycling markets, with glass, stones and concrete recycled as a secondary aggregate. Donarbon says that if markets can't be found for all the plastics, some may be used for power generation as refuse-derived fuel. When fully operational, the sorting area will work on a two eight-hour shift basis on weekdays, while the composting hall will operate continuously. When up and running, the plant should create 20 new jobs.

Donarbon and the council are particularly proud of the education/visitor centre being built, which features two viewing windows overlooking the mechanical sorting area and the composting hall. "We plan to link the work of the education centre to the national curriculum as there is a requirement under it to study environmental issues, particularly recycling," says Shelton.

The construction and dry commissioning phase of the MBT facility is scheduled for completion next month, followed by a further 12-month commissioning phase to ensure the process meets its targets. In November 2010, the plant should be fully operational.

Maxine Perella is editor of LAWR

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