A new process for tackling the safe disposal of Britain’s growing mountain of unwanted tanalised timber – now barred from landfill after being classed as hazardous waste – has been devised by chemists at the Manchester processing site of Southampton-based waste management specialist Cleansing Service Group.
The timber, used widely in industrial and domestic construction projects from cooling towers to garden sheds, has been impregnated with a polluting preservative called chromated copper arsenate. The preservative bonds with the wood and is difficult to remove.
It has already been banned or restricted in the USA and many European countries, and the Government’s new Landfill Directive declared it a hazardous waste demanding strict disposal requirements.
Since then, the timber has become a kind of ‘stateless waste stream’ with no obvious graveyard in which to dispose of it.
It is illegal to dispose of it in landfill facilities taking inert construction waste such as bricks and builders’ rubble, or in ‘non-hazardous’ sites due to the hazardous concentration of arsenic. And because it’s an organic material it can’t go into ‘hazardous’ sites either.
The only alternative has been incineration, but this can release dangerous pollution into the atmosphere and there are only two or three incinerators in the country with the sophisticated scrubbing capacity to remove arsenic from the off gases.
The combined capacity of these incinerators is not great enough to handle the huge volumes of polluted timber now being stockpiled across the country, probably running into thousands of tons.
Last year, CSG gained Environment Agency permission to begin trials of a new treated wood disposal process at its waste treatment and recycling plant at Cadishead, near Manchester.
The process is now fully permitted by the EA and the plant has successfully processed over 1000 tonnes, mainly from demolished cooling towers .
The wood is shredded and then washed to extract the hazardous contaminants. The washings are further treated to form a residual ‘cake’ destined for hazardous waste landfill. The shredded wood is clean enough to be disposed of at a non hazardous landfill or a composting facility.
CSG managing director Paul Quigley said: “Huge volumes of this wood have been stockpiled on our customers’ sites since the introduction of the Landfill Directive because they didn’t know how to dispose of it. It had become a disposal hazard. Incineration and landfill were either not practical or illegal and they were just hoping something else would come along.
“We’ve got the infrastructure at our Cadishead site to succesfully devise a process for dealing with this disposal problem on an industrial scale by adapting existing shredding and aqueous treatment technology.
“The vast majority of people in the waste industry couldn’t contemplate doing it because the scale of the plant and storage space required are prohibitive.
“Waste disposal habits only change in response to new regulations. The cheapest option invariably prevails and in the past landfill has been that option. As far as polluted timber is concerned, that ceased to be an option when the Landfill Directive came into force and we’ve now developed a process in response to that.”