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.
The current project was initiated to address the utilization of the lignin component obtained during the bioconversion of aspenwood wastes. This utilization is necessary for the economic viability of the whole conversion process. The lignin obtained from steam pretreatment has been suggested to be of low molecular weight, reactive, and offer great potential as a raw material for utilization. This is in contrast to the lignins from traditional pulping operations. However previous to this work, characterizati- on of lignin separated after steam pretreatment of aspenwood under varying conditions (with and without acidic catalysts), has not been undertaken to substantiate these widely held beliefs. Neither has anyone identified the production of the type of lignin most suitable for various applications. A prerequisite for utilization of this material, therefore, has been to undertake this necessary characterization. A major emphasis of the work during this first year has been placed on the establishment of the analytical capability required to achieve the above goals. Following discussions with other researchers, such as Glasser and Lewis (Virginia Tech.), Chum (SERI), etc. we are confident the analytical methodology we have in place for lignin characterization and the assessment of planned modification reactions is as good as any other laboratory in the world.
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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. An experiment was initiated to determine whether wood treated with carbon-based preservatives could be degraded by composting without residual preservative contamination. After one year the concentration of azoles remained high, while the concentration of DDAcarbonate was greatly reduced. Several fungal isolations were made from the compost mixtures. More time is needed to complete the composting process.