The absence of commercial facilities to recycle or recover value from wood treated with metal-based wood preservatives at the end of its service life is one of the most significant negative points in the generally positive life cycle analysis of treated wood. Wood treated with carbon-based preservatives (metal-free) may be far easier to recycle or recover value from since the preservatives are relatively vulnerable to thermal, chemical and biological breakdown. As a result they might be destroyed by kraft pulping, combustion or composting of treated wood. The present research evaluates the use of carbon-based preservative-treated wood in these processes.
Kraft pulps produced from wood freshly treated with recommended loadings of carbon-based preservatives contained significant quantities of didecyldimethylammonium carbonate (DDAcarbonate), propiconazole and tebuconazole. However, lower preservative concentration in the wood and intensive pulping may be able to produce pulps without detectable preservatives. The azoles were also detected in significant quantities in the black liquor (DDAcarbonate was not analysed in black liquor).
No azoles were found in the ash produced from combustion, but significant quantities were detected in the filtered smoke. DDAcarbonate was not detected in the filtered smoke. Analysis of DDAcarbonate in ash was inconclusive.
A composting experiment has been set up and is in progress. Data on preservative breakdown during composting is expected next year.