Thursday 26 March 2020

Greenwich Materials Recycling Facility

By Richard Buchanan

The Blackheath Scientific Society had a visit to the Greenwich Materials Recycling Facility on 16 Jan 2007. Numbers were limited to ten. Unlike other Councils, the Greenwich philosophy is to ask people to put all dry waste in one blue top bin, and to collect it with a single lorry. They then separate it at a mixed, dry, recycling plant. 

The plant occupies a big grey building at the far end of Nathan Way, Plumstead. Mr Peter Dalley, the manager, took us round, on a first floor walkway, and showed us the various machines which are linked by rising conveyor belts. The day we went there was much rubbish on the floor under the conveyors, and paper/plastic separation did not seem as good as it might have been, though presumably acceptable.

The first process is bag splitting, so any pre-sorting one might have done is nullified. Then oversized items are removed with a Trommel Screen, to be manually sorted. This is followed by a Ballistic Separator (a large spinning drum) which does an initial sort of containers from paper. Containers are separated into iron, aluminium and glass: a Magnet (people with pacemakers are not let on the visit) takes out iron cans etc; an Eddy Current separator removes aluminium; leaving glass. Plastic bags, paper and a residue remain. An infra-red lamp detects Plastic and drives a puffer machine to separate it from paper. Paper is sorted first automatically, and then manually - it is important that no glass gets into it, though small wispy pieces of plastic are tolerated. The last piece of equipment is a Baler. Some incoming waste, such as bulk paper from a business, can go straight to the baler. 

Depending on market prices, particularly for plastics, extra manual sorting can be done. Manual Sorters work two or three to a room about 6 m (20 ft) square, for seven hour days, no shift lasting more them four hours. The plant is run with a staff of about 20 per shift.

Mr Dalley took questions afterwards and outlined future plans. He gave various prices: Paper for newsprint earns £250 per ton; Cleanaway, who take the baled waste, put up £6m towards the cost of the plant; National Land Fill permits come with a fine of £150/ton for excess; and an EU fine of F/Wday; a waste disposal lorry costs £125,000; wheelie bins for 120, 240 & 330 litre capacity cost £25, £18 & £40. 

At present 72% of residents voluntarily use blue top bins, and produce high grade waste. It is proposed to revise the use of bins so that all residents use blue-top bins for dry waste and green-top bins for kitchen and garden waste – with weekly collection for both. Other waste would be put in a bag and collected fortnightly. Biodegradble Cornstarch bags would be used for kitchen waste - fitting in a kitchen container, tied off when full and put in the green-top bin. 

It is proposed to build an anaerobic digester for green waste so that methane given off as it rots can be fed to a Combined Heat and Power plant (better than a garden compost bin venting to the atmosphere). If restaurant waste were properly sorted this too would be taken and would improve digester efficiency. Other by-products would be a good quality top soil and liquid fertiliser, both useable by the Council. In the future it might be worthwhile to adapt the digester to produce hydrogen

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