Remediation of materials with mixed contaminants treatability, technology and final disposal
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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