19 October 2001

Grinding out a good result

is their game

Increasing pressure on

councils to provide

household and municipal

green waste recycling sites

could be a useful means of

diversification. Andy Moore

spoke to one contractor

who is actively involved in

the business

WHEN Bracknell Forest Borough Council approached Shorts Services to start a green waste recycling operation eight years ago, it was confident the firm had the necessary resources to run what would become a rapidly expanding enterprise.

Based in Ascot, Berks, Shorts Services already had years of experience in municipal waste management and needed to bolster its farm contract services which are only carried out on a seasonal basis.

"We have always been involved in providing contract services for livestock farms and green waste recycling appeared to be a suitable bolt-on business," says Gary Short, director of Shorts Services. "Taking on a waste recycling enterprise has enabled us to fully utilise our farm buildings and machinery which were redundant during quiet periods of the year."

The contractors also had to match the councils ambitious recycling targets which were to increase dramatically over the next 15 years.

Under the governments Waste Strategy 2000 scheme, 18% of household waste is to be recycled or composted by 2003, with a target of 27% by 2005 and 35% for 2015. These figures are based on the amount of waste which was dumped in landfill sites in 1995.

Meeting such objectives over the councils 12,145ha (30,000 acre) jurisdiction has enabled Shorts recycling business to expand. It now supplies the men and machinery to process more than 2500t of green waste evey year on the councils behalf.

The majority of green waste, such as tree branches and grass/hedge clippings, are produced from municipal areas including parks, woods and roadsides. And if 2500t/year is not enough to keep the contractors busy, Bracknell Forest Borough Council aims to supply Shorts with another 3000t of green waste produced by households over the next year.

Raymond Whitehead, environmental services manager for the council, believes processing green waste produced by the public will play a big part in meeting the targets of the Waste Strategy 2000 scheme.

"We set up a civic amenity disposal site last year to encourage the public to dispose their green waste in an environmentally friendly fashion," says Mr Whitehead. "Landfill tax is to increase from £12 to £30/t over the next few years which the council and taxpayer will have to bear the brunt of."

Green waste is carefully pre-sorted and checked by the council to ensure it contains no contaminants and is transported to Shorts grinding and composting site at Winkfield, five miles from Ascot.

Stockpiled into large heaps, the green waste is then loaded by telehandler into a US-built DuraTech HD-10P grinder.

Mutilating material up to 30cm (1ft) in diameter is done by 36 hammers mounted on a rotor which runs at a formidable 2100rpm. The rotor is driven directly from a 500hp Caterpillar engine through a slip clutch.

Similar to a tub diet feeder, material is rotated inside a hydraulically-driven 3m diameter barrel before falling onto the hammer mill rotor.

Material is chopped against a concave screen with a 20cm x 15cm (8in x 6in) mesh to achieve a uniform chop length, which enables the chippings to quickly decompose into a high quality compost.

"The tub grinder produces a more even chop length than shredders which tend to cut material using a horizontal rotor," says Mr Short. "Running at 2100rpm, the machine can chew its way through 100cu m of waste an hour and consume 300 litres of fuel over an eight-hour day."

To prevent indigestion, the grinder has an electronic governor to regulate oil flow to the tub drive in proportion to the engine speed. Further overload protection is provided by the slip clutch, while an automatic shutdown facility stops the machine in the unlikely event it comes across something too large for it to handle.

"Although it takes a lot to bring the grinder a halt, over-size branches and contaminants can sometimes stop the machine working," says Mr Short. "Replacing the 36 tungsten carbide-tipped hammers costs £1000."

These high running costs are retrieved by charging the council by the hour rather than by the tonne, says Mr Short. And because the council pays rent and lease costs for Shorts barns and machinery, the contracting firm claims to reap a healthy return.

Viable enterprise

This arrangement, or charging the waste supplier a £15-£20/t gate fee, could form a viable enterprise for contractors and farmers wanting to diversify. If a gate fee is charged and compost is produced solely in-house, farmers and contractors could sell the finished compost at £5-£15/cu m, says Mr Short.

For the machine to be operated to its full capacity, he believes 300t of green waste should be in-situ prior to the start of loading.

After green waste is processed, the chippings fall onto a conveyor, while a height adjustable elevator deposits them into a triangular-shaped windrow ready for composting.

"The windrow is turned at least once a fortnight using a telehandler to ensure the compost is mixed thoroughly and a 60C temperature is maintained," says Mr Short. "This allows aerobic activity to be maintained so that high value, fertile compost can be produced over a 16 to 20-week period."

Using a telehandler, the compost is then separated into 10mm or 25mm chop lengths using a Powerscreen Trommel machine and loaded into a silage shed.

Mr Short says the shed is ideal for containing any effluent and for the compost to be better preserved for further screening.

After the completed compost has been stored in the barn, the material is loaded onto 14t trailers and transported back to the councils depot, where it is used in horticultural applications such as top soil for shrub borders.

The remaining compost is spread onto agricultural land using 15t Richard Western rear discharge muck spreaders. &#42

Bottomless pit…the US-built DuraTech HD-10P is powered by a 500hp Caterpillar engine and is capable of processing 100cu m of waste an hour.

Screened compost worth £5-£15/cu m is loaded in 14t trailers and delivered back to the council.

Gary Short: "Green waste recycling has proven an ideal bolt-on business next to our agricultural contracting services."