Browsing by Subject "Dioxin"
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Item Combustion Emissions from d-RDF (Densified-Refuse Derived Fuel) Pellets: Bench-Scale Studies(University of Minnesota Duluth, 1994-01) Leak, Vance GA series of smoldering combustion tests were performed on samples of d-RDF (densifiedrefuse derived fuel) and clean wastepaper pellets over the temperature range of 400°-800°C in l00°C increments. These tests attempted to simulate the inadequate combustion conditions often found in small industrial or residential airtight heating stoves A high value of 729 pg/g of 2,3,7,8 TCDD (dioxin) was produced in the replicate 700°C (- l,250°F) tests on the d-RDF pellets. At 800°C no dioxin was detected in the ash samples. The d-RDF ash also contained a variety of heavy metals in significant amounts. The clean wastepaper pellets, by contrast, produced a clean ash over the same smoldering (low-oxygen) combustion temperatures. The ash from these pellets contained low levels of both the primary dioxin and the heavy metals. While it appears that the wastepaper pellets are suitable for a convenience fuel for small industrial or residential heating stoves, the d-RDF pellets do not seem suitable for this purpose. The d-RDF pellets seem to be best utilized in larger furnace industrial and institutional applications where proper combustion and stoichiometric controls can be maintained. This would ensure that the dioxins are destroyed by the high temperature combustion conditions and the ash and flue dust materials can be properly managed.Item Desorption from Contaminated Sediment and the Organic-Carbon Normalized Sediment-Water Partition Coefficient, Koc, for Dioxin(University of Minnesota Duluth, 1998-09) Lodge, Keith B; Cook, P.M.We use the “solids concentration effect” in an attempt to measure the organic-carbon normalized sediment-water partition coefficient, Koc, for 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin) using desorption from contaminated sediment from Lake Ontario. The sediment was collected from Station 208 (Onuska et al., J. Great Lakes Res. 9(2), 169-182, 1983); it contains 470 pg/g dry weight of dioxin and 2.37% of organic carbon. We prepared a series of sediment suspensions of decreasing solids concentration; after various periods of equilibration followed by separation of sediment solids and water by sedimentation, we analyzed the aqueous phase for dioxin and organic carbon. The ranges of solids concentration (Cs,w ), of total aqueous phase dioxin (Clc,w ), and of aqueous phase organic carbon (Coc,w) are 0.06-60 g/L, 2-1000 pg/L, and 0.23-65 mg/L respectively. For the measured partition coefficient, Kmoc , our data fit the functions, log Kmoc = a constant - log Cs,w, and log Kmoc = a constant - log Csorb,w; values of R2 range from 0.61 to 0.92. Csorb,w is related to the organic carbon content of the water by Csorb,w = Coc,w - 0.2 mg / L; the prime indicates that the aqueous organic carbon levels are corrected for blank contributions. The total aqueous phase dioxin concentration only depends strongly on the concentration of organic carbon when Coc,w > 0.2 mg / L. We think this is an example of the phenomenon described by the term “critical micelle concentration”, CMC, which is usually reserved for the description of surfactant solutions, but here we have evidence that it applies to natural organic carbon also. For the system here the CMC is about 0.2 mg/L. By spiking the apparatus with C13-labeled dioxin, we are able to judge the degree to which the system has reached equilibrium or steady state. We establish clearly thereby that the dioxin in the water is at steady state in four experiments. Another feature is the recovery of the settled sediment solids at the end of experiments, and we show that the dioxin concentration, on a dry weight basis, decreases; levels are in the range 230-380 pg/g. This begs the question: What is the organic-carbon normalized dioxin concentration in the sediment at the end of the experiment? With assumptions, mass balance shows that significant quantities of organic carbon are adsorbed on the walls of the apparatus, and it appears that equilibrium is reached when concentrations of dioxin on organic material in the sediment, in the water and on the walls of the apparatus are the same. When doing partitioning experiments at low solids in large apparatus, it is important to recover the settled solids, and determine the level of adsorbed chemical and the organic carbon content. Then, we can complete the mass balance and determine uniquely the quantities of material adsorbed to the walls of the apparatus. Work with less hydrophobic compounds than dioxin shows that Kmoc becomes independent of solids concentration as the solids concentration decreases, whence Koc = Kmoc. We did not reach a sufficiently small concentration of solids; however, we are able to conclude that for dioxin Koc > 7.1; this observation agrees with other partitioning work done with dioxin and its isomers.Item Toward the Understanding of Phenomena Affecting the Measurement of Octanol-Water Partition Coefficients for Hydrophobic Chemicals: Studies with DDT and Dioxin(University of Minnesota Duluth, 1995-08) Lodge, Keith B; Moser, D. Edelbach; Kohlbry, S. W