Innovative MBT
Caelia Quinault visits Donarbon's soon-to-be completed MBT facility in Cambridgeshire

When waste management firm Donarbon won Cambridgeshire county council's £730 million waste treatment contract in March 2008, it was renowned for being one of the first small-to-medium-sized enterprises to break into the waste PFI market.

Yet on entering Donarbon's site at Waterbeach, five miles north of Cambridge, it is immediately clear that there is nothing small about this company or the work it has undertaken.

The enormous 500 acre site, occupying rural land off the A10, was first bought by Donarbon's parent company, the Dickerson Group, for the extraction of sand and gravel after the Second World War. In 1969, Donarbon was formed as a skip hire business to make use of the void that was left and the site soon became a mainly landfill operation, winning Cambridgeshire county council's landfill contract in the late 1990s.

When Cambridgeshire county council went out to tender for its long-term waste treatment contract, Donarbon proposed to extend its operations by developing a mechanical biological treatment (MBT) plant which would remove recyclable material from 179,000 tonnes of black bag waste a year and then compost it to produce a soil conditioner.

Competition
The bid fought off competition from a proposal by WRG to develop an incinerator, and a proposal by Shanks to build an MBT plant producing solid recovered fuel — partly because of the unpopularity of burning waste in Cambridgeshire, but also because of cost.

"On price and quality the Donarbon bid won", explains Mark Shelton, waste promotions manager at Donarbon, who had the unique position of helping to select the company as preferred bidder in his former role as waste policy officer for Cambridgeshire county council.

"Donarbon was lucky in that, for Cambridgeshire, it has the infrastructure. There are not many small companies that have that."

Today, it is clear that the confidence Cambridgeshire placed in Donarbon is already starting to pay off. After the plant was granted planning permission "without a single objection", and Donarbon secured £60 million from the Bank of Ireland just before the recession, work started in April 2008 and today the facility is nearing completion.

This is in large part thanks to the partnership between Donarbon and its principal contactor, the Dutch-based civil engineering company BAM Nuttall. "It is amazing how far we have come," Mr Shelton comments. "The site looks remarkably like the architect's picture already. We are ahead of our target and we should be able to take in our first waste in November this year — giving us a year for reliability testing before the contract starts officially."

Process
The MBT facility comprises three main chambers, all constructed around steel frames. It has a curved roof to make it look "more like a science park than a waste facility", and is flanked by an education centre, a large water tank in case of fire and an air treatment plant.

Giles Brookes, project manager for BAM Nuttall, explains that when black bag waste is delivered to the plant from November, it will come into the reception hall, where machines will split the bags open and slightly shred the material. Already, much of the machinery is in place.

"It will then be transferred to a conveyor belt in a second hall, where it will be mechanically sorted using 62 conveyor belts and technology provided by German specialist Komptech. This includes two trommels, a hard particle separator to remove stone and glass, a star screen, overhand magnets to remove ferrous metals, an eddy current separator to remove aluminium, brini separator and a near infra red (NIR) separator to separate two dimensional and three dimensional plastic," he says.

Nick Balmer, business development manager for waste at BAM Nuttall, adds: "The plant is very unusual in that it will not have hand pickers. It was an aspiration of myself and Mark Davenport's (Donarbon's managing director) to avoid it — especially as there is the issue of where you would get the people from in future years."

The waste will then be shredded in a Crambo machine where water is added to it, before it is taken by overhead conveyor belts to the third and largest composting chamber, which measures 73 metres wide and 200 metres long, and deposited on the floor.

Turning
This is where the plant's crowning glory comes in. A 35 metre-wide Compost Turning Machine produced by Austrian technology provider Kelag has already been installed and sits on wheels which run along a track down the length of the hall and has a giant wheel to pick up waste and throw it forwards. The machine is the first of its kind in the UK, but the ninth in the world, and will help aerate the waste and ensure that it stays at a consistent temperature allowing the waste to biodegrade in just seven weeks.

Air will also be sucked through the material via buried channels to aid the composting process and leachate is siphoned off. The leachate will be recycled for use in the Crambo machines and the air will be sent for cleaning through a biofilter, acid scrubbers and wet woodchips before being discharged to the atmosphere.

Mr Brookes explains: "This is a very controlled environment, not affected by weather which provides the perfect conditions for biodegrading." During the whole MBT process, Donarbon claims that the waste will be reduced by 25% through material extraction and a further 25-30% through the composting process — leaving just 45 50% of the original, which could potentially be sent to a variety of end markets.

Mr Shelton explains that, by allowing the waste material to reach temperatures of 70-80 degrees Celsius, the output will be compliant with the Animal By Product Regulations, which require pathogens to be killed.

However, he says that the material would never meet the PAS 100 standard for compost — meaning that it could only be deemed a compost-like output (CLO) and could not be used by farmers growing food crops.

To get around this problem, Donarbon expects to use the material to restore the Dickerson Group's quarries and to grow non-food crops, such as those used for energy. Accreditation for this can only be awarded by the Environment Agency after the plant is up and running, when officers can inspect the CLO.

However, the company is confident that, even if accreditation is not awarded, the plant will enable Cambridgeshire county council to meet its targets to divert municipal biodegradable waste from landfill under the Landfill Allowance Trading Scheme (LATS) — because of the ability of the MBT process to reduce the biodegradability of the waste.

With a 51% recycling rate, Cambridgeshire is already on track to meet its 2010 targets, but it will need the MBT to meet targets in 2013 and 2020.

Mr Shelton explains: "The manufacturers claim that the biodegradability of the waste will be reduced by 70% so even if we have to landfill the material we will have LATS to spare and Cambridgeshire should meet its targets." In fact, Donarbon expects that the plant will be able to process so much waste that it might even be able to cater for the needs of neighbouring local authorities alongside Cambridgeshire in the short term.

With many waste projects suffering in the recession, Donarbon and BAM Nuttall's MBT plant is proving a welcome success story — steaming ahead of similar projects being undertaken in Lancashire, Manchester and Norfolk. Mr Balmer said: "We have come and hit the ground running.

"It is amazing to think this was a green field just 12 months ago. The biggest question is why technology like this is not being rolled out elsewhere."

Article courtesy of Resource Management and Recovery - 01/05/2009


Further Info
Peter Bishop - Head of Public Relations & Corporate Communication
BAM Nuttall Limited
St James House, Knoll Road, Camberley,
Surrey GU15 3XW
Tel: 01276 63484
Fax:01276 66060
peter.bishop@bamnuttall.co.uk