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- Löthgren, Carl-Johan, 1968-
(författare)
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Mercury and dioxins in a MercOx-scrubber
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The removal of mercury and the absorption of dioxins in an acid wet scrubber have been studied in industrial scale. Hydrogen peroxide is added as an oxidizing agent to the scrubber liquid with the purpose to remove SO2 and enhance the removal of mercury. The scrubber is operating as the final flue gas cleaning stage at the SAKAB plant, a hazardous waste incinerator in Sweden. Mercury speciation was measured in flue gases upstream and downstream of the scrubber with three different techniques: Impingers, solid phase absorbents and a continuous emission monitor. During the flue gas sampling periods also the scrubber liquid was sampled. It was found that mercury entering the scrubber is efficiently oxidized at normal operating conditions. An increased fraction of elemental gaseous mercury was found in flue gases after the scrubber at redox potentials below 700 mV and pH below 1. The mercury emissions were more dependent on the scrubber liquid composition than on the inlet concentrations. Equilibrium calculations of the mercury speciation in the scrubber liquid and flue gases after the scrubber showed that mercury is normally emitted as HgBr2 or HgCl2. Elemental bromine and chlorine are formed in the scrubber. Both species probably take part in the mercury oxidation process. Results from 18 months of dioxin sampling, using a continuous long term sampling device (the AMESA system) were evaluated by multivariate data analyses. It was shown that the elevated emissions observed were caused by a memory effect in the scrubber due to high start-up concentrations. The memory effect was modelled in a diffusion model where the dioxins were considered to be physically absorbed in and desorbed from the polypropylene fillings of the scrubber. From the diffusion model, the diffusivities for tetra to hexa chlorinated dioxins in polypropylene were calculated. The diffusivity of tetra chlorinated dioxins was calculated to be 10-14 m2/s. The diffusivity decreases with increasing chlorination. For hexa chlorinated dioxins it was calculated to be 10-16 m2/s. Brominated dioxins were measured before and after a fabric filter. The fraction of brominated dioxins increased after the filter. Di brominated furans were the most abundant homologue.
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| 2. |
- Elgh-Dalgren, Kristin, 1980-
(författare)
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Remediation of materials with mixed contaminants : treatability, technology and final disposal
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Contaminated soils are a large issue worldwide and much effort has been made to find efficient remediation methods. At many contaminated sites, mixtures of different contaminants with different properties are present, which may lead to additional problems, and thus additional costs, during the remediation process. This thesis presents the results from soil remediation of two mixed contaminated soils, containing explosives and heavy metals and polycyclic aromatic hydrocarbons (PAH) and arsenic, respectively. The results demonstrate that bioremediation may be an efficient method for moderate explosives concentration, but that too high contaminant concentrations may prevent the biodegradation, measured by both chemical and ecotoxicological analyses. If the contaminant concentration is very high, soil washing with alkaline pH (~12, NaOH) may be a good alternative, which was observed to remove both explosives and heavy metals. For a PAH and arsenic contaminated soil, little degradation of organics was observed during the bioremediation. However, the arsenic present was re-distributed in the soil, which could potentially lead to increased availability and thus increased risk for contaminant spreading. Soil washing at alkaline pH (~12-13; Ca(OH)2) with a combination of a biodegradable non-ionic surfactant and a biodegradable chelating agent, executed at high temperature (50°C), reached treatment goals for both arsenic and PAH after 10 min treatment. Measurement of ecotoxicity using Microtox® demonstrated that remaining surfactant in the soil may lead to increased toxicity despite lower contaminant concentrations. Soil is a basically non-renewable resource and thus re-cycling of remediated soil ought to be commonly occurring. Yet, the re-cycling of remediated masses has so far been limited in Sweden, mainly because of the risk of spreading of pollutant remains. However, a recent proposition from the Swedish EPA opens for re-cycling, even though the thresholds are very conservative. Risk assessment of the remediated soil includes the utilization of leaching tests to estimate the risk of spreading of remaining pollutants. A comparison of the leaching from four remediated soils using three different leaching solutions reveals that leaching of both heavy metals and PAH occurs. In addition, differences between different legislations were observed, which could imply that the same soil could be re-cycled in one country (the Netherlands) but not another (Sweden).
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