Just add water and, look, no more toxic waste: Earth's most plentiful substance opens new horizons in chemical and weapons disposal, says Anna Coyle

A NEW environmentally friendly method of destroying hazardous wastes, explosives and chemical weapons that relies only on water is being developed by chemists on both sides of the Atlantic.

At normal atmospheric pressure, water boils at 100C. As mountaineers know, at high altitudes - and correspondingly lower pressures - water does not have to be heated as much to reach boiling point. So the temperature at which water changes from liquid to vapour or gas increases steadily with increasing pressure - but the relationship holds only up to a point.

At high temperature and pressure, the clear distinction between gas and liquid disappears. The material, then known as a supercritical fluid, becomes a hybrid, with some properties of a liquid but others that are gas-like.

The supercritical state, which for water is beyond 374C and 218 atmospheres pressure, endows water with many seemingly bizarre characteristics compared with the liquid or vapour, and it is these that chemists are trying to harness.

The most useful is its ability to dissolve almost anything, for example oils and hydrocarbons that normally separate out in water. This makes it a unique medium for chemical reactions, bringing together substances that do not normally dissolve in the same liquid; ideal for the complex brew of chemicals that make up most industrial wastes.

The aqueous fluid is also highly reactive. Dissolved oxygen in the water is often all that is needed to trigger a chain of reactions that may not even be possible with an oxidising agent many times more powerful than bleach and a metal or acid catalyst. This super-reactivity can reduce even the largest complex organic molecule to carbon dioxide and a few other simple species.

Dr Anthony Clifford, in the chemistry department at the University of Leeds, has been researching the properties of supercritical water, focusing on the speed of the reactions. 'The reactions occur extremely quickly, up to 100 times faster than ordinary chemical reactions,' he says.

The aim of his team's work is to design a practical system for the safe destruction of a broad spectrum of toxic waste. Dr Clifford is confident that this can be achieved - although it may take 10 years to accomplish because understanding of the chemistry that takes place in the medium is still hazy. 'We are still collecting basic information,' he says. 'The reactions are not understood well enough to do them on a large scale.'

Dr Clifford's work is part of a collaboration with the chemical engineering department of Imperial College, London, and the National Engineering Laboratory at East Kilbride in Scotland.

The medium shows promise for the continuing problem of disposal of polychlorinated biphenyls, or PCBs. Their use has been restricted since the late Seventies, when their extreme toxicity and persistence in the environment was recognised.

But more than 40 years of widespread industrial use, in applications as diverse as electrical transformers and capacitors to hydraulic fluids and paints, has left a huge amount of material to destroy. Specially designed incinerators, operating at temperatures above 1,100C, are the only effective solution at present.

Supercritical water may be a less energy-intensive, environmentally preferred alternative within a few years. Chemists have shown that an aqueous solution of PCBs and oxygen in the supercritical state completely destroys the lethal chloride material in minutes, at least on a laboratory scale, leaving only small benign species such as carbon dioxide. The solutions can then be safely disposed of in rivers or the sea.

'It also has the environmental advantage that the chlorine ends up as chloride dissolved in water,' Dr Clifford says. 'And there is plenty of chloride in the sea already.'

Other supercritical fluids are used as solvents for extraction in industrial processes. The best known is carbon dioxide, which removes caffeine from green coffee beans and fat from low- fat crisps. Carbon dioxide has the huge advantage of becoming critical at a mere 31C and 71 atmospheres.

Supercritical water requires temperatures and pressures 10 times higher, but 375C is cool compared with incinerator temperatures. Special pressure vessels are needed, but the closed system means that, unlike an incinerator, there are no emissions into the atmosphere.

A drawback is that the water is highly corrosive and affects stainless- steel reactors and even normally inert materials such as gold or platinum alloys. Dr Clifford does not think these properties will act as a major deterrent to exploiting the water-based medium. 'As the technology to overcome them is available, these disadvantages become cost and convenience factors to weigh against potential advantages,' he says.

The American military has been investigating the potential for chemical destruction by supercritical water since the phenomenon was first observed in the early Seventies. The environmentally non-intrusive nature of the technology adds to its attractiveness for the chemical weapons' destruction to which the US is committed, as well as for disposing of redundant stocks of other military chemicals such as propellants and

explosives.

With this aim, the Armed Services Committee of Congress recently allocated dollars 180m ( pounds 121m) of its dollars 10bn ( pounds 6.7bn) research budget to support development work.

Dr Clifford, who is a member of the panel reviewing the topic for the US Army, thinks the technology will find similar application in Britain. 'In the past the problem has been swept under the carpet,' he says. 'Weapons from the Second World War that are buried underground can be dug up and disposed of by the end of the millennium using this technology.'

(Photograph omitted)

Start your day with The Independent, sign up for daily news emails
News
Legendary blues and rock singer Joe Cocker has died of lung cancer, his management team as confirmed. He was 70
people70-year-old was most famous for 'You are So Beautiful'
News
people
Sport
Chelsea manager Jose Mourinho
footballLatest score and Twitter updates
Arts and Entertainment
David Hasselhof in Peter Pan
The US stars who've taken to UK panto, from Hasselhoff to Hall
PROMOTED VIDEO
ebooks
ebooksA year of political gossip, levity and intrigue from the sharpest pen in Westminster
Life and Style
Approaching sale shopping in a smart way means that you’ll get the most out of your money
life + styleSales shopping tips and tricks from the experts
News
newsIt was due to be auctioned off for charity
Life and Style
A still from a scene cut from The Interview showing North Korean leader Kim Jong-un's death.
tech
Environment
Sir David Attenborough
environment... as well as a plant and a spider
Voices
'That's the legal bit done. Now on to the ceremony!'
voicesThe fight for marriage equality isn't over yet, says Siobhan Fenton
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Ashdown Group: IT Support Technician - 12 Month Fixed Term - Shrewsbury

£17000 - £20000 per annum: Ashdown Group: IT Helpdesk Support Technician - 12 ...

The Jenrick Group: Maintenance Planner

£28000 - £32000 per annum + pension + holidays: The Jenrick Group: Maintenance...

The Jenrick Group: World Wide PLC Service Engineer

£30000 - £38000 per annum + pesion + holidays: The Jenrick Group: World Wide S...

The Jenrick Group: Project Manager

£35000 per annum + Pension+Bupa: The Jenrick Group: We are recruiting for an e...

Day In a Page

Surrounded by high-rise flats is a little house filled with Lebanon’s history - clocks, rifles, frogmen’s uniforms and colonial helmets

Clocks, rifles, swords, frogmen’s uniforms

Surrounded by high-rise flats is a little house filled with Lebanon’s history
Return to Gaza: Four months on, the wounds left by Israel's bombardment have not yet healed

Four months after the bombardment, Gaza’s wounds are yet to heal

Kim Sengupta is reunited with a man whose plight mirrors the suffering of the Palestinian people
Gastric surgery: Is it really the answer to the UK's obesity epidemic?

Is gastric surgery really the answer to the UK's obesity epidemic?

Critics argue that it’s crazy to operate on healthy people just to stop them eating
Homeless Veterans appeal: Christmas charity auction Part 2 - now LIVE

Homeless Veterans appeal: Christmas charity auction

Bid on original art, or trips of a lifetime to Africa or the 'Corrie' set, and help Homeless Veterans
Pantomime rings the changes to welcome autistic theatre-goers

Autism-friendly theatre

Pantomime leads the pack in quest to welcome all
The week Hollywood got scared and had to grow up a bit

The week Hollywood got scared and had to grow up a bit

Sony suffered a chorus of disapproval after it withdrew 'The Interview', but it's not too late for it to take a stand, says Joan Smith
From Widow Twankey to Mother Goose, how do the men who play panto dames get themselves ready for the performance of a lifetime?

Panto dames: before and after

From Widow Twankey to Mother Goose, how do the men who play panto dames get themselves ready for the performance of a lifetime?
Thirties murder mystery novel is surprise runaway Christmas hit

Thirties murder mystery novel is surprise runaway Christmas hit

Booksellers say readers are turning away from dark modern thrillers and back to the golden age of crime writing
Anne-Marie Huby: 'Charities deserve the best,' says founder of JustGiving

Anne-Marie Huby: 'Charities deserve the best'

Ten million of us have used the JustGiving website to donate to good causes. Its co-founder says that being dynamic is as important as being kind
The botanist who hunts for giant trees at Kew Gardens

The man who hunts giants

A Kew Gardens botanist has found 25 new large tree species - and he's sure there are more out there
The 12 ways of Christmas: Spare a thought for those who will be working to keep others safe during the festive season

The 12 ways of Christmas

We speak to a dozen people who will be working to keep others safe, happy and healthy over the holidays
Birdwatching men have a lot in common with their feathered friends, new study shows

The male exhibits strange behaviour

A new study shows that birdwatching men have a lot in common with their feathered friends...
Diaries of Evelyn Waugh, Virginia Woolf and Noël Coward reveal how they coped with the December blues

Famous diaries: Christmas week in history

Noël Coward parties into the night, Alan Clark bemoans the cost of servants, Evelyn Waugh ponders his drinking…
From noble to narky, the fall of the open letter

From noble to narky, the fall of the open letter

The great tradition of St Paul and Zola reached its nadir with a hungry worker's rant to Russell Brand, says DJ Taylor
A Christmas ghost story by Alison Moore: A prodigal daughter has a breakthrough

A Christmas ghost story by Alison Moore

The story was published earlier this month in 'Poor Souls' Light: Seven Curious Tales'