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The influence of soil and contaminant properties on the efficiency of physical and chemical soil remediation methods
Umeå University, Faculty of Science and Technology, Chemistry.
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.

Place, publisher, year, edition, pages
2009. , 76 p.
Keyword [en]
Fenton’s reagent, ozone, solvent washing, granular activated carbon, GAC
National Category
Environmental Sciences
Research subject
Cardiology
Identifiers
URN: urn:nbn:se:umu:diva-21040ISBN: 978-91-7264-763-3 (print)OAI: oai:DiVA.org:umu-21040DiVA: diva2:210495
Public defence
2009-04-24, KB3B1, KBC-huset, Umeå Universitet, 901 87 Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2009-04-03 Created: 2009-04-01 Last updated: 2009-04-03Bibliographically approved
List of papers
1. Comparison of Fenton's Reagent and Ozone Oxidation of Polycyclic Aromatic Hydrocarbons in Aged Contaminated Soils
Open this publication in new window or tab >>Comparison of Fenton's Reagent and Ozone Oxidation of Polycyclic Aromatic Hydrocarbons in Aged Contaminated Soils
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2006 (English)In: Journal of Soils and Sediments, ISSN 1614-7480 (Online), Vol. 6, no 4, 208-214 p.Article in journal (Refereed) Published
Abstract [en]

Background, Aim and Scope: Polycyclic aromatic hydrocarbons (PAHs) are formed as a result of incomplete combustion and are among the most frequently occurring contaminants in soils and sediments. PAHs are of great environmental concern due to their ubiquitous nature and toxicological properties. Consequently, extensive research has been conducted into the development of methods to remediate soils contaminated with PAHs. Fenton's reagent or ozone is the most commonly studied chemical oxidation methods. However, the majority of remediation studies use soils that have been artificially contaminated with either one or a limited number of PAH compounds in the laboratory. Hence, it is essential to extend such studies to soils contaminated with multiple PAHs under field conditions.

Objectives. The objective of this study is to investigate the capacity of Fenton's reagent and ozone to degrade PAHs in soils. The soils have been collected from a number of different industrial sites and, therefore, will have been exposed to different PAH compounds in varying concentrations over a range of time periods. The capacity of Fenton's reagent and ozone to degrade PAHs in industrially contaminated soils is compared to results obtained in studies using soils artificially contaminated with PAHs in the laboratory.

Materials and Methods: Nine soil samples, contaminated with PAHs, were collected from five different industrial sites in Sweden. For the Fenton's reagent procedure, the pH of the soil slurry samples was adjusted to pH 3 and they were kept at a constant temperature of 70ºC whilst H2O2 was added. For the ozone procedure, soil samples were mixed with 50% water and 50% ethanol and kept at a constant temperature of 45 ºC. Ozone was then continually introduced to each soil sample over a period of four hours. Following the Fenton's reagent and ozone oxidation procedures, the samples were filtered to isolate the solid phase, which was then extracted using pressurized liquid extraction (PLE). The sample extracts were cleaned up using open columns and then analysed by gas chromatography-mass spectrometry (GC-MS).

Results: The relative abundance of the detected PAHs varied between soils, associated with different industries. For example, low molecular weight (LMW) PAHs were more abundant in soil samples collected from wood impregnation sites and high overall PAH degradation efficiencies were observed in soils originating from these sites. In the contaminated soils studied, PAHs were more effectively degraded using Fenton's reagent (PAH degradation efficiency of 40-86%) as opposed to ozone (PAH degradation efficiency of 10-70%). LMW PAHs were more efficiently degraded, using ozone as the oxidizing agent, whereas the use of Fenton's reagent resulted in a more even degradation pattern for PAHs with two through six fused aromatic rings.

Discussion: The degradation efficiency for both methods was largely dependent on the initial PAH concentration in the soil sample, with higher degradation observed in highly polluted soils. LMW PAHs are more susceptible to degradation than high molecular weight (HMW) PAHs. As a result of this the relative abundance of large (often carcinogenic) PAHs increased after chemical oxidation treatment, particularly after ozone treatment. Repeated Fenton's reagent treatment did not result in any further degradation of soil PAHs, indicating that residual soil PAHs are strongly sorbed. The effectiveness of the two oxidation treatment approaches differed between industrial sites, thus highlighting the importance of further research into the influence of soil properties on the sorption capacity of PAHs.

Conclusions: This study demonstrates that the degree to which chemical oxidation techniques can degrade soil bound PAHs chemical degradation is highly dependent on both the concentration of PAHs in the soils and the compounds present, i.e. the various PAH profiles. Therefore, similarities in the PAH degradation efficiencies in the nine soil samples studied were observed with the two chemical oxidation methods used. However, the degradation performance of Fenton's reagent and ozone differed between the two methods. Overall, Fenton's reagent achieved the highest total PAH degradation due to stronger oxidation conditions. LMW PAHs showed higher susceptibility to oxidation, whereas high molecular weight (HMW) PAHs appear to be strongly sorbed to the soils and therefore less chemically available for oxidation. This study highlights the importance of including soils collected from a range of contaminated sites in remediation studies. Such soil samples will contain PAH contaminants of varying concentrations, chemical and physical properties, and have been aged under field conditions. In addition to the chemical and physical properties of the soils, these factors will all influence the chemical availability of PAHs to oxidation.

Recommendations and Perspectives: We recommend including aged contaminated soils in chemical degradation studies. In future chemical remediation work, we intend to investigate the potential influence of the chemical and physical properties of PAHs and soil parameters potential influence on the chemical oxidation efficiency in aged contaminated soils.

Due to the vast number of contaminated sites there is a great need of efficient remediation methods throughout the world. This study shows the difficulties which may be experienced when applying remediation methods to a variation of contaminated sites.

Place, publisher, year, edition, pages
Berlin: Springer, 2006
Keyword
aged contaminated soils, chemical oxidation, coke production, degradation, Fenton's reaction, gas works, ozone oxidation, polycyclic aromatic hydrocarbons (PAHs), soil remediation, wood impregnation
Identifiers
urn:nbn:se:umu:diva-12414 (URN)10.1065/jss2006.08.179 (DOI)
Available from: 2007-08-13 Created: 2007-08-13Bibliographically approved
2. Degradation of polycyclic aromatic hydrocarbons (PAHs) in contaminated soils by Fenton's reagent: a multivariate evaluation of the importance of soil characteristics and PAH properties
Open this publication in new window or tab >>Degradation of polycyclic aromatic hydrocarbons (PAHs) in contaminated soils by Fenton's reagent: a multivariate evaluation of the importance of soil characteristics and PAH properties
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2007 (English)In: Journal of Hazardous Materials, ISSN 0304-3894, E-ISSN 1873-3336, Vol. 149, no 1, 86-96 p.Article in journal (Refereed) Published
Abstract [en]

In this study, we investigated how the chemical degradability of polycyclic aromatic hydrocarbons (PAHs) in aged soil samples from various contaminated sites is influenced by soil characteristics and by PAH physico-chemical properties. The results were evaluated using the multivariate statistical tool, partial least squares projections to latent structures (PLS). The PAH-contaminated soil samples were characterised (by pH, conductivity, organic matter content, oxide content, particle size, specific surface area, and the time elapsed since the contamination events, i.e. age), and subjected to relatively mild, slurry-phase Fenton's reaction conditions. In general, low molecular weight PAHs were degraded to a greater extent than large, highly hydrophobic variants. Anthracene, benzo(a)pyrene, and pyrene were more susceptible to degradation than other, structurally similar, PAHs; an effect attributed to the known susceptibility of these compounds to reactions with hydroxyl radicals. The presence of organic matter and the specific surface area of the soil were clearly negatively correlated with the degradation of bi- and tri-cyclic PAHs, whereas the amount of degraded organic matter correlated positively with the degradation of PAHs with five or six fused rings. This was explained by enhanced availability of the larger PAHs, which were released from the organic matter as it degraded. Our study shows that sorption of PAHs is influenced by a combination of soil characteristics and physico-chemical properties of individual PAHs. Multivariate statistical tools have great potential for assessing the relative importance of these parameters.

National Category
Natural Sciences Environmental Sciences
Research subject
Chemistry
Identifiers
urn:nbn:se:oru:diva-5304 (URN)10.1016/j.jhazmat.2007.03.057 (DOI)17513044 (PubMedID)
Available from: 2009-02-03 Created: 2009-02-03 Last updated: 2017-12-14Bibliographically approved
3. Dioxin removal from contaminated soils by ethanol washing
Open this publication in new window or tab >>Dioxin removal from contaminated soils by ethanol washing
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2010 (English)In: Journal of Hazardous Materials, ISSN 0304-3894, E-ISSN 1873-3336, ISSN 0304-3894, Vol. 179, no 1-3, 393-399 p.Article in journal (Refereed) Published
Abstract [en]

The aim of this study was to investigate the potential utility of ethanol washing for remediating soils contaminated with polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), as a cost-efficient alternative to conventional remediation methods of PCDD/F-contaminated soils. Initially, screening experiments were performed with a two-level full factorial design to examine the effects of temperature, extraction time and ethanol concentration on the removal efficiency. The screening experiments showed that the ethanol concentration was the most important parameter. In addition, repeated washing cycles considerably improved the results. Ethanol washing conditions were then selected (10 wash cycles with 75% ethanol at 60 °C), and applied to four soils with different soil characteristics and contamination levels to test the robustness of the selected method. Treatment efficiencies of 81% and 85% were obtained for a lightly contaminated sandy–silty soil and a highly contaminated clay soil rich in graphite particles, respectively. Even higher treatment efficiencies (≥97%) were obtained for two other highly contaminated soils, one of which contained high amounts of organic matter. PCDD/Fs were found to both dissolve in the solvent and migrate into it as species adsorbed to particles. The relative contributions of these mechanisms and the overall efficiency of the removal seem to depend on contaminant concentration, the types of carbon in the soil matrix and the particle size distribution. The study shows that ethanol washing has effective remediation potential for a variety of PCDD/F-contaminated soils.

 

Place, publisher, year, edition, pages
Elsevier, 2010
Keyword
Soil remediation, pollutants, PCDD, PCDF, solvent washing
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-21008 (URN)10.1016/j.jhazmat.2010.03.017 (DOI)000278626700054 ()
Available from: 2009-04-01 Created: 2009-03-31 Last updated: 2017-12-13Bibliographically approved
4. Granular activated carbon (GAC)- extraction of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans from soil washing liquids of contaminated soils
Open this publication in new window or tab >>Granular activated carbon (GAC)- extraction of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans from soil washing liquids of contaminated soils
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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
Soil remediation, pollutants, PCDD, PCDF, solvent washing, carbon, adsorption
Identifiers
urn:nbn:se:umu:diva-21009 (URN)
Available from: 2009-04-01 Created: 2009-03-31 Last updated: 2010-01-14Bibliographically approved

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