benzofurans and chromated-copper-arsenate

The performance and removal mechanisms of a hybrid constructed wetland (HCW) followed by a willow planted filter (WPF) were evaluated for the treatment of a leachate contaminated by wood pole preservatives (pentachlorophenol (PCP) and chromated copper arsenate) to reach the storm sewer discharge limits. The HCW aimed to dechlorinate the PCP and polychlorodibenzo-p-dioxins/polychlorodibenzofuran (PCDD/F) and to remove metals by adsorption and precipitation. The HCW was efficient in removing PCP (>98.6%), oil, arsenic (99.4%), chromium (>99.2%), copper (>99.6%%) and iron (29%) to under their discharge limits, but it was unable to reach those of Mn and PCDD/F, with residual concentrations of 0.11 mg Mn/L and 0.32 pg TEQ/L. Iron and manganese could be removed but were subsequently released by the HCW due to low redox conditions. No dechlorination of PCDD/F was observed since its chlorination profile remained the same in the different sections of the HCW. Adsorption was the most probable removal mechanism of PCDD/F. The WPF was able to remove some residual contamination, but it released Mn at a gradually decreasing rate. Total evapotranspiration of the leachate by a larger fertilized WPF and the construction of an underground retention basin are proposed to prevent any discharge of PCDD/F traces in the environment.

Topics: Adsorption; Arsenates; Benzofurans; Chromium; Copper; Pentachlorophenol; Polymers; Salix; Wetlands; Wood

Aged and weathered chromated copper arsenate (CCA) treated wood was burned in an open burn research facility to characterize the air emissions and residual ash. The objectives were to simulate, to the extent possible, the combustion of such waste wood as might occur in an open field or someone's backyard; to characterize the composition and particle size distribution (PSD) of the emitted fly ash; to determine the partitioning of arsenic, chromium, and copper between the fly ash and residual ash; and to examine the speciation of the CCA elements. This work reports preliminary air emission concentrations and estimated emission factors for total particulate matter, arsenic (As), chromium (Cr), copper (Cu), and polychlorinated dibenzodioxins/dibenzofurans (PCDD/F) totals and toxic equivalents (TEQs). The partitioning of As, Cr, and Cu between the emitted fly ash and residual ash is examined and thermochemical predictions from the literature are used to explain the observed behavior. Results indicate a unimodal fly ash PSD between 0.1 and 1.0 microm diameter. In addition to a large carbonaceous component, between 11 and 14% of the As present in the burned CCA treated wood was emitted with the air emissions, with the remainder present in the residual ash. In contrast, less than 1% of both the Cr and Cu present in the wood was emitted with the air emissions. PCDD/F levels were unremarkable, averaging 1.7 ng TEQ/kg of treated wood burned, a value typical for wood combustion. Scanning electron microscopy (SEM) was unable to resolve inorganic particles consisting of Cu, Cr, or As in the wood samples, but X-ray absorption fine structure (XAFS) spectroscopy confirmed that the oxidation states of the CCA elements in the wood were Cu2+, Cr3+, and As5+. SEM examination of the fly ash samples revealed some inorganic microcrystals within the mostly carbonaceous fly ash, while XAFS spectroscopy of the same samples showed that the oxidation states after combustion were mixed Cu+ and Cu2+, Cr3+, and mixed As3+ and As5+. Estimates of the ratios of the mixed oxidation states based on the XAFS spectra were As3+/(total As) = 0.8-0.9 and Cu+/(total Cu) = 0.65-0.7. The Cu and Cr present in the fly ash were determined to coexist predominantly in the two oxide phases CuCrO2 and CuCr2O4. These results indicate that the open burning of CCA-treated wood can lead to significant air emissions of the more toxic trivalent form of As in particle sizes that are most respirable.

Topics: Air Pollutants; Arsenates; Arsenic; Benzofurans; Chromium; Conservation of Natural Resources; Copper; Dibenzofurans, Polychlorinated; Incineration; Polychlorinated Dibenzodioxins; Refuse Disposal; Soil Pollutants; Wood

Bottom ash that was the result of the combustion of chromated copper arsenate (CCA) treated wood under controlled fire conditions showed an increase of several orders of magnitude in the levels of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), compared to that of untreated timber. Wood that has been pressure treated with CCA contains copper (II), which is known to catalyse the so-called de novo formation of PCDD/Fs. Comparable levels of PCDD/Fs would be expected in residual ash from burning CCA-treated wood in backyard fires, stoves and wood heaters, as a consequence of similar combustion conditions.

Topics: Air Pollutants; Arsenates; Benzofurans; Catalysis; Copper; Dibenzofurans, Polychlorinated; Fires; Polychlorinated Dibenzodioxins; Refuse Disposal; Wood

Ash residues from fires of radiata pine timber, both untreated and treated with chromated copper arsenate (CCA), were analyzed for the presence of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F). Fire conditions were simulated using a cone calorimeter. The sensitivity of the magnitude and profile of PCDD/F in the ash under controlled experimental conditions were examined to gain an insight into the formation of PCDD/F in a system containing CCA. The total amount of PCDD/F increased from 2.0 ng/kg of ash (0.05 ng of TE/kg of ash, using WHO-TEF) for untreated radiata pine to a maximum of 2700 ng/kg of ash (78 ng of TE/kg of ash) for 0.94% CCA. Ash containing CCA showed a distinct preference for formation of PCDFs, particularly the tetrachloro homologue. It is concluded that PCDD/F formation predominantly occurred via de novo synthesis during smoldering of the char rather than during the initial flaming and pyrolysis. Furthermore, the composition of the CCA constituents present in the timber was controlled to assess whether the physical presence of Cu, a known catalyst in PCDD/F production, was sufficient to account for the formation of PCDD/F in fires of timber impregnated with CCA.

Topics: Air Pollutants; Arsenates; Benzofurans; Dibenzofurans, Polychlorinated; Environmental Monitoring; Fires; Incineration; Polychlorinated Dibenzodioxins; Soil Pollutants; Wood