Waste Options

 

 

Incineration

Dangers from burning CCA-Treated Timber
Bushfires and Fire-Wood
Identifying CCA-Treated Timber
Research into Safer Incineration Methods
References

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Dangers from burning CCA-Treated Timber

Combustion of CCA treated timber involves a number of environmental hazards. Ash from CCA-treated timber contains elevated levels of heavy metals. Once burnt, the ash continues to leach heavy metals. Solo-Gabriele et al (2003a) confirmed CCA-treated wood ash exceeded the 5 mg/L regulatory level for total arsenic leaching under the US EPA standards. The CSIRO warns that the ash from burnt CCA-treated timber on rural properties should be removed or buried away from stock, as the ‘salty contaminated ash … can cause problems’ (CSIRO, 2002). The smoke can also contains high levels of arsine gas and dioxins: ‘Studies show that, depending on the combustion conditions, 10-90% of the arsenic present in CCA-treated wood’ may go up in the smoke (APVMA, 2003a: 47).

Australian research by Tame et al (2003), has tested ash from burnt CCA-treated pine for polychlorinated dioxins (dibenzo-p-dioxins) and furans (polychlorinated dibenzofurans, PCDD/F), well-known atmospheric pollutants. They concluded that these pollutants formed mainly during the smouldering of the char (ash), raising concerns about the impacts after bushfires in residential areas, such as Canberra during 2002. In Canberra 55 sites were contaminated with treated timber ash. Site remediation required removal of 2000 tons of soil, took a year to complete and cost around $3,000,000 (Godson, W. Pers. Comm., 27/2/05)

The APVMA review recognised the risks associated with incineration and warned that it ‘should only occur in very controlled facilities where release of arsenic to the atmosphere is minimised and the potentially highly toxic ash is processed and disposed of appropriately.’ For this reason the authority recommends that CCA chemical labels be varied to prevent waste CCA-treated timber from being incinerated (APVMA, 2003a, p.47). However because of its limited powers the APVMA is not able to regulate potential incineration, although it could have made recommendations on this.

Incineration of CCA-treated timber is in fact banned in some states including NSW. EPA Victoria (2003) has raised concerns about horticulturalists who burn waste such as CCA-treated timber and has fined at least one grapegrower in 2003 for this because of the ‘significant risk to human health, the environment and the clean green image…’ The South Australian EPA warns that ‘Children, pets and farm animals should be excluded from land where CCA ash is present [for example after bushfires]. Animals will want to lick or eat the salty residue and young children, especially those under 5 years, are at high risk from personal contact and ingestion. Animal deaths from ingesting ash have previously been reported on farms in the USA and UK’ (SA EPA, 2005).

Bushfires and Fire-Wood

CCA-treated timber may be incinerated accidentally as a result of house fires and bushfires, or by people ignorant of its dangers when they dispose of waste treated timber in backyard burn-offs. People can also put treated timber into garbage streams that go to municipal incinerators. Fire-fighting organizations such as the country fire services are aware of the hazards associated with burning CCA but seldom know, when they attend a fire, whether the burning timber is CCA.

Perhaps of most concern is the fact that people sometimes burn it in their indoor home fireplaces, without realizing the dangers that they are exposing their families and neighbours to. Because traditional sources of heating wood are becoming scarce and therefore more expensive, scrap timber and off-cuts from building sites are turned to as free sources of timber. ‘It is not uncommon to see this rubbish wood, including treated pine etc, piled high in Canberra backyards… not only treated pine but other treated timbers’ (Darryl Johnston, Pers. Comm. 1/8/03).

Identifying CCA-Treated Timber

CCA-treated timber may also be incinerated when it is mixed with other wood that is used as fuel wood. Often waste wood piles contain some CCA-treated wood, so that it would be hazardous to use them for fuel. Previous research found that ‘visual sorting’, based on the colour of the treated timber, is not accurate. To prevent the ash being classified as hazardous in the US, wood reused for fuel must contain less than five percent of CCA-treated timber (Solo-Gabriele, et al, 2001).

A more specific method for identifying CCA-treated timber is through a stain test. Although this is a workable method, the cost and time required to administer the stain were of particular concern to large recycling facilities. Solo-Gabriele et al (2001) claim that the Laser Induced Breakdown Spectroscopy (LIBS) and X-ray Fluorescence Spectroscopy (XRF) that they are developing will provide a faster and cheaper method for sorting waste wood. However both technologies have technological drawbacks and are not ready for commercial use. A trial of a portable hand held X ray device called a XRF metal analyser is being used at Medley USA.

Research into Safer Incineration Methods

Some research into safer controlled incineration methods that would capture the arsenic and toxic residues has begun but it is in its early states. At the University of Sydney’s Chemical Engineering laboratories, research is underway into the possibilities of incinerating CCA-treated timber to recover both the energy as well as the metals (as environmentally stable residues). So far, the researchers have found that at temperatures greater than 400°C the copper and chrome are contained in the ash, while the arsenic is volatilized. The researchers are aiming to recover all three metal components from the waste wood (Stewart et al, 2004).

In earlier work undertaken at the University of Sydney for the Western Sydney Waste Board, it was found that at a combustion temperature of 900oC, energy was more efficiently produced than in pyrolysis and gasification at lower temperatures, and arsenic (present as arsenate) was produced in a stable form. The researchers noted that the arsenic produced as off-gas was a concern, although if combusted in a flash smelter such as those used in the copper industry, the arsenic could probably be captured (CRESTA, 2000). Solo-Gabriele et al (2001) report that in Europe pyrolysis technology appears to be further advanced, with ‘two full-scale pyrolysis operations’ in France which claim to recover most of the heavy metals.

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