Hydrothermal Treatment of CCA- and Penta-Treated Wood
Keywords:CCA, hazardous and solid wastes, PAHs, penta, preservative-treated wood, supercritical water, transformation/recovery/recycling
AbstractTwo of the three most commonly used wood preservatives in the United States are chromated copper arsenate (CCA) and oil-borne pentachlorophenol (penta). Both are excellent preservatives for extending the service life of exterior wood. Both also pose environmental problems associated with their disposal. This paper describes the treatment of two different groups of preservative-treated wood (CCA type C and oil-borne penta) in anaerobic supercritical water (SC) under acidic and basic conditions, respectively. A decommissioned (ca. 13 yr) southern pine (Pinus sp.) guard rail impregnated with CCA and a freshly treated pentaimpregnated pole were examined. During SC treatments, wood particles were transformed (approx. 98% efficiency) into liquid and gaseous hydrocarbon (HC) phase. The metals recovered in the two liquid phases vs. total concentration in the wood were as follows: copper: 91% AQ; < 1% HC, chromium: 28% AQ; 1.3% HC, and arsenic: 69% AQ; < 1% HC. The penta wood yielded a similar hydrocarbon mixture, with the chlorinated phenols undergoing dechlorination and further reaction. The formation of phenolic condensation products such as chlorinated dibenzofurans and dioxins occurred under these conditions when the reaction was run in quartz-lined containers and metals were excluded from the reaction mixture. When iron (either from the reactor walls or added in quartz cells as iron particles) was present, these products were not observed.
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