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How complex science deals with our waste
WHEN dustmen collect household waste the general view is that it’s thrown into a giant hole in the ground and left to rot.
But there is more going on than initially meets the eye.
Behind the scenes at any landfill site is a complex operation to bury, seal and control the process of decomposing waste in a process that can last decades.
Ardley Fields, a recycling centre and landfill site, is run by waste firm Viridor, and deals with around 150,000 tonnes of waste every year.
Each day refuse trucks and other waste carrying lorries are weighed in. They then dump their waste on a large concrete square and go back out on the county’s streets to collect more.
For each tonne of rubbish put in landfill at Ardley the Government now collects £72 in taxes.
In 2012/13 Oxfordshire County Council spent £6m on landfill tax.
One of the big issues for landfill operators is controlling the release of methane gas which is produced by rotting waste.
Methane is an odourless, colourless, flammable gas, which is a potent greenhouse gas when released into the atmosphere and can contribute to global warming.
But by burning it in a controlled manner it can generate electricity.
In order to do this an extensive network of pipes is laid in the waste to suck out the methane and transport it to a control plant to be processed.
Each year the site generates 3.2 megawatts of electricity which is fed into the National Grid. That is the equivalent to the electricity consumed by around 5,500 homes each year.
Waste firm Viridor operate the 94-hectare site and have an Environment Agency permit to operate as a landfill facility until 2019.
Henry Austin, site manager
Henry Austin, site manager, said the landfill facility was a 24/7 operation.
The site is mainly regulated by the Environment Agency and Oxfordshire County Council, which make regular visits to check all is in order and that the site is running safely. Mr Austin said: “There are all sorts of regulations to make sure everything is recorded and people are following the rules and there is no fraudulent activity.”
As well as checks, Viridor carries out internal and external audits.
It is also accredited by the British Standards Institute for environmental quality, health and safety and management systems.
Mr Austin said the firm would be based in Ardley for the long haul.
He said: “We as licence or permit holders have responsibility for the site.
“We have to show the Environment Agency there is no more potential for the site to pollute.
“There has not been a site around that has reached that stage yet. We are likely to be here decades, if not centuries.”
Next year the firm’s energy from waste incinerator will open at the site. It will burn up to 300,000 tonnes of waste each year.
Championed by Oxfordshire County Council, the incinerator will reduce the cost in landfill taxes paid to the Government each year, the local authority says.
Since 2000 the amount of waste sent to landfill in Oxfordshire has decreased every year from 86.2 per cent to currently 39.98 per cent.
Recycling has increased from 13.8 per cent in 2000 to 60.02 in 2012/13.
It comes after district councils introduced doorstep recycling schemes for general ‘dry’ recycling such as paper, card, electricals and glass, and composting waste such as green and food waste.
COST OF LANDFILL
PEOPLE in Oxfordshire are good at recycling, says the county council, and in 2012/13 the authority was the best in the UK at recycling and composting.
But we could do better. In 2012/13 the council spent £6m on landfill tax – then it was paying £64 per tonne. Prices have gone up to £72 per tonne and the projection is a spend of about £8m.
Council spokesman Martin Crabtree said: “Landfill tax is a tax on the disposal of waste. It aims to encourage people to produce less waste, recover more value from it through recycling or composting and to use more environmentally-friendly methods of waste disposal.”
Only items that can’t be recycled should then go to landfill but the reality is different. At Ardley there is little sorting done once trucks empty their waste so anything thrown out will more than likely be buried forever.
Waste has changed over the years. Workers used to see more organic matter and these days see more plastic.
FILLING THE HOLES
Holes at the former quarry are called cells and are quite literally filled with rubbish.
Each cell is built like a giant bund, is lined with a specialist plastic at the bottom, and its sides built up with soil and clay.
It is about five metres deep below the pit edge, over about two hectares, and on average it takes two years to fill a cell.
Rubbish is piled high and each day a compactor, with large spikes, is driven over the top to squash the waste down.
Once it is full, the waste is piled high, in a mound shape, and over the next five years will sink as the waste decomposes.
A digger picks up rubbish to fill a cell
Each cell is engineered so waste water – called leachate – cannot leak out of it.
Once it is full the cell is capped. Leachate and methane continue to be pumped out of it for years.
Mr Austin said: “Landfill gas is produced as waste degrades. Various types of bacteria work on the waste and create the landfill gases.
“When each area is restored we drill gas wells within about two-thirds through the waste mass.
Methane is pumped out of the degrading waste
“We put in pipes – up to 200 mm diameter – which create a pathway up through the waste for landfill gas.
“We need the pipes as methane is burnt to generate electricity rather than going into the atmosphere.
“The piping is realistically forever. It (methane) won’t be commercially viable for ever, the volume and quality tail off. There’s about 30 years’ commercial viability.”
The site also deals with dangerous waste such as asbestos, which is buried in a separate corner.
Eventually the land will flatten as waste decomposes.
This bubbling liquid is leachate, the run-off water from decomposing waste.
It is treated in a similar way to sewage.
Billions of micro-organisms “chomp” their way through the leachate until it is cleaned and then it is put through Bicester’s sewage system.
AS the waste decomposes the waste sinks and the mounds start to level off.
Then begins the restoration process. Soil about a metre deep is laid on top of the sealed cell and it is then grassed over and left for nature to reclaim.
If trees or hedges are going to be planted the depth increases to a metre-and-a-half.
The elusive great crested newt is said to be in abundance at the site because the habitats are left alone with just sheep grazing the land.
If fact the only tell-tale sign that under the grass is thousands of tonnes of rubbish is the pipe sticking out above ground.
THE BIRDMAN OF ARDLEY
Birds of prey are used to chase scavenging birds such as crows, gulls and rooks away from the active landfill site.
Dale Atkinson is a regular at Ardley with his falcons and hawks to stop scavenging birds from picking over rubbish and carrying it across the countryside.
HISTORY OF THE SITE
THE land was originally excavated for limestone by Smiths of Bloxham. In the early 1980s it started as a landfill operation.
Limestone dug out would have been used for building roads and homes, and rubble brought to the site is now recycled for projects, including building the M40.
Haul Waste Ltd, now Viridor, took over the site in the 1980s and still run it today.
Site manager Henry Austin says the quarry floor is just how it was left by Smiths, and there is still limestone there.
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