Science: Hellfire in the belly of a green machine: Garbage in, clean power out - that's the promise of a generating plant that burns domestic waste. But do its environmental claims pass the test? Nicholas Schoon reports

A huge power station has just been completed near the heart of London. It runs on garbage. Few know about it, apart from those living in the shadow of its 330ft chimney. Media talk about London power stations is confined to the likely fate of Bankside and Battersea, those redundant brick- built giants beside the Thames.

There is something very British in being so interested in turning industrial dinosaurs into leisure parks and art galleries while ignoring a pioneering power station a few miles down river in Deptford.

Alas, there is nothing very British about the brand-new pounds 95m SELCHP incinerator that will consume nearly half a million tons of rubbish a year. It is largely financed, owned, built and operated by French firms. Much of the technology and engineering is German.

The world's first electricity-generating rubbish incinerator was built in Britain, in Oldham in 1895, according to Bob Wheatley, managing director of the company that owns SELCHP - South East London Combined Heat and Power.

Their time has come round again; expect between five and 20 to be built in Britain by 2000. Greenpeace loathes them but I came away from visting SELCHP believing they are exciting, highly practical, if imperfect, green machines.

The greatest thrill was the hellish sight through a small, thick-glassed window into the bottom of one of the two furnace/boilers, the size of a house: a fire-filled room raged with pieces of rubbish exploding into flames and flying around in the powerful draughts.

Garbage produces a third as much heat, weight for weight, as coal when burnt. The SELCHP plant takes in the rubbish of some 300,000 homes and generates 32 megawatts of electricity, enough for 30,000 households.

The volume of garbage is reduced by 90 per cent in burning and its weight by two thirds, slashing the amount of space taken up in landfill dumps. Iron-containing waste, mainly cans, is yanked out of the ash by electromagnets. SELCHP will produce 20,000 tons of scrap iron a year.

The Government, green groups and much of the waste industry all agree that Britain relies too much on landfilling garbage - about 90 per cent of it goes into holes in the ground. There it rots, producing noxious liquids that can contaminate rivers and aquifers, and methane gas, which is a contributor to man-made global warming.

(Much of this methane can be collected in pipes and burnt to produce electricity, but far more of the energy in the rubbish can be captured by burning it directly).

But incineration is no alternative, say many environmentalists. They fear the spread of waste-to-energy plants such as SELCHP will only encourage the bad habits of a resource-hungry, throw-away society. Instead, they emphasise minimising the quantity of waste households produce (largely by using less packaging), increasing recycling projects and converting the 'putrescibles' (mainly food scraps and garden waste) into compost.

They see incinerators as being in conflict with recycling and composting, because it is the paper, plastic and putrescibles that make garbage burn.

Wrong, says Mr Wheatley. Among materials easiest to recycle are glass and metal, which do not burn. As far as incineration is concerned, the more of them removed from garbage the better. And, he says, there will always be some plastic and paper that cannot be recycled because it has food or more unpleasant material stuck to it.

Incineration and recycling can grow together, he argues. Conflicts will only arise once well over half of all household waste is being recycled, a point that will not be reached for decades.

Less easily dismissed are worries that incinerators cause pollution. The SELCHP plant has enormous, expensive devices for removing noxious materials from the gases emerging from the furnace. To begin with, the temperature has to be kept above 850C for more than two seconds in order to minimise the production of dioxins - highly persistent toxic chemicals formed in small quantities when garbage is burnt at lower temperatures.

Powdered charcoal and a mixture of lime and water are then injected into the exhaust gases. These remove one of the most abundant pollutants, corrosive hydrochloric acid, and toxic heavy metals such as mercury and cadmium. Finally, the gases are forced through hundreds of fabric bags to filter out dust before going up the chimney.

The dust is collected by mechanically shaking the bags; the plant will produce 18,000 tons a year. It contains fairly high levels of heavy metals and is classified as a hazardous waste.

The plant is allowed to produce one billionth of a gram of dioxins per cubic metre of exhaust gas but, says Mr Wheatley, it is producing far less. He estimates that seven years will pass before a whole gram of dioxin has emerged from the chimney.

Most of what does emerge is water vapour, air and carbon dioxide. The exhaust is invisible, apart from on cold, damp mornings when a plume of steam can be seen.

SELCHP sucks in vast amounts of air around its roof to blow through the furnaces. In doing so, it removes the smells wafting from all the garbage waiting to be burnt.

But in spite of all this pollution abatement engineering, many of the plant's neighbours have been hostile and fearful. Although the incinerator is hemmed in by two busy railway tracks and a small industrial estate, the nearest homes are only 200 yards away.

When the plant began operating, the main environmental problem turned out to be noise. Nearby residents have been complaining about a rushing sound that appears to come from the chimney and plagues them at night. After some heavy- duty tinkering with pounds 3m's worth of noise abatement equipment, Mr Wheatley hopes the problem has now been cracked.

SELCHP has been financed on the basis of 30-year contracts to dispose of the waste collected by the London boroughs of Lewisham and Greenwich, plus a guaranteed high price for its power which is subsidised by electricity consumers.

The compulsory subsidy, set up by the government to encourage alternatives to the use of coal, oil and gas in power generation, means the plant earns 7.1p for each unit of electricity sold compared with the a market price of 2.5p. This actually encourages the plant to burn garbage wastefully. But when the subsidy expires in 1998 Mr Wheatley hopes SELCHP can sell heat as well as power, boosting the incinerator's efficiency.

The plan is to pipe hot water to 7,500 flats on six nearby council estates, providing all of their warmth and hot water and substituting for oil-fired boilers. Used in this mode, the plant really is a green machine. It generates less power but wastes only 30 per cent of the total energy produced by the burning garbage compared with 50 per cent wastage when generating electricity alone.

For now, Mr Wheatley wants to improve the quality of the garbage entering the plant. The huge grabs which pick up several tons at a time and hoist them to the top of the furnace can conceal surprisingly large items. SELCHP has burnt shopping trolleys, even a motorbike. Fortunately none of these bulkier items has yet damaged the machinery. But, said Mr Wheatley, 'We have to keep nagging our suppliers.'

(Photographs and graphic omitted)