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Granular activated carbon (GAC)- extraction of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans from soil washing liquids of contaminated soils
Umeå University, Faculty of Science and Technology, Chemistry.
Umeå University, Faculty of Science and Technology, Chemistry.
Umeå University, Faculty of Science and Technology, Chemistry.
Umeå University, Faculty of Science and Technology, Chemistry.
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(English)Manuscript (Other academic)
Abstract [en]

Ethanol washing has been recently shown to be a potentially useful technique for remediating soils contaminated with polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). During this process, the contaminants are transferred from the soils to the washing liquid, producing a highly toxic extract. Consequently, there is a need for a post-treatment technique that removes the PCDD/F from the washing liquid, enabling its recirculation. In this study, the potential utility of granular activated carbon (GAC) as an adsorbent for extracting PCDD/Fs from soil-washing liquids was investigated. The washing liquids were produced by extraction of two former sawmill sites, at which chlorophenol based preservatives had been used. The PCDD/F levels in the washing liquids were 42 and 540 pg TEQ PCDD/F /g soil, and the organic contents in the soils differed greatly prior to the washing procedure. Ten 80 mL aliquots of the extracts of each soil, each corresponding to approximately 25 g of soil, were treated with 0-1.5 g GAC to adsorb the contaminants. In both cases, a removal efficiency of 96% was attained, but 15-fold more GAC was needed to clean the liquid used to treat the soil with the high organic content to this degree (1.5 g versus 0.1 g for the liquid used to wash the other soil). Hence, the extraction efficiency of the GAC treatment appears to be influenced by the amount of organic matter in the soil, probably due to competition between PCDD/F and other organic compounds (natural organic matter and other contaminants) in the soil for the GAC adsorption sites, since GAC adsorbs non-specifically. The results in this study provide promising indications that GAC can be used to remove dioxins from soil-washing liquid, thereby facilitating recirculation and reducing treatment costs. We also propose a number of additional procedures that may be needed for a complete soil-solvent washing process.

Keyword [en]
Soil remediation, pollutants, PCDD, PCDF, solvent washing, carbon, adsorption
URN: urn:nbn:se:umu:diva-21009OAI: diva2:210299
Available from: 2009-04-01 Created: 2009-03-31 Last updated: 2010-01-14Bibliographically approved
In thesis
1. The influence of soil and contaminant properties on the efficiency of physical and chemical soil remediation methods
Open this publication in new window or tab >>The influence of soil and contaminant properties on the efficiency of physical and chemical soil remediation methods
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

 A vast number of sites that have been contaminated by industrial activities have been identified worldwide. Many such sites now pose serious risks to humans and the environment. Given the large number of contaminated sites there is a great need for efficient, cost-effective  remediation methods. Extensive research has therefore been focused on the development of such methods. However, the remediation of old industrial sites is challenging, for several reasons.

One major  problem is that organic contaminants become increasingly strongly sequestered as they persist in the soil matrix for a long period of time. This process is often referred to as ‘aging’, and leads to decreasing availability of the contaminants, which also affects the remediation efficiency. In the work underlying this thesis, the influence of soil and contaminant properties on the efficiency of various physical and chemical soil remediation methods was investigated. The investigated contaminants were polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs).

Briefly, the results show that as the size of soil particles decreases the contaminants become more strongly sorbed to the soil’s matrix, probably due to the accompanying increases in specific surface area. This affected the efficiency of the removal of organic pollutants by both a process based on solvent washing and processes based on chemical oxidation. The sorption strength is also affected by the hydrophobicity of the contaminants. However, for a number of the investigated PAHs their chemical reactivity was found to be of greater importance for the degradation efficiency. Further, the organic content of a soil is often regarded as the most important soil parameter for adsorption of hydrophobic compounds. In these studies the effect of this parameter was found to be particularly pronounced for the oxidation of low molecular weight PAHs, but larger PAHs were strongly adsorbed even at low levels of organic matter. However, for these PAHs the degradation efficiency was positively correlated to the amount of degraded organic matter, probably due to the organic matter being oxidized to smaller and less hydrophobic forms. The amount of organic matter in the soil had little effect on the removal efficiency obtained by the solvent-washing process. However, it had strong influence on the performance of a subsequent, granular activated carbon-based post-treatment of the washing liquid.

In conclusion, the results in this thesis show that remediation of contaminated soils is a complex process, the efficiency of which will be affected by the soil matrix as well as the properties of the contaminants present at the site. However, by acquiring thorough knowledge of the parameters affecting the treatability of a soil it is possible to select appropriate remediation methods, and optimize them in terms of both remediation efficiency and costs for site- and contaminant-specific applications.

76 p.
Fenton’s reagent, ozone, solvent washing, granular activated carbon, GAC
National Category
Environmental Sciences
Research subject
urn:nbn:se:umu:diva-21040 (URN)978-91-7264-763-3 (ISBN)
Public defence
2009-04-24, KB3B1, KBC-huset, Umeå Universitet, 901 87 Umeå, 13:00 (English)
Available from: 2009-04-03 Created: 2009-04-01 Last updated: 2009-04-03Bibliographically approved

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