Methods to improve the remediation of polycyclic aromatic hydrocarbons (pahs) in aerobic and anaerobic environments

Oil spills occur regularly in terrestrial environments and crude oil can contain many compounds that are highly resistant to degradation. Among these compounds are high levels of polycyclic aromatic hydrocarbons (PAHs) which are not only toxic but can also be carcinogenic and/or mutagenic. The first chapter of this dissertation includes an extensive review chapter on the variables affecting the anaerobic degradation of hydrocarbons, with a particular focus on PAHs. Electron acceptors, electron donors, temperature, salinity, pH all play key roles in determining the possibility effective of effective degradation occurring. Thus, by addressing solutions, such as biostimulation, improving environmental variables for optimal growth and enzymatic rates, and increasing the supply of the electron acceptors needed for anaerobic respiration help to remove obstacles to biodegradation. Additionally, the use of co-substrates or techniques such as bioaugmentation can further enhance this endeavor. Aerobic hydrocarbon degradation also has its challenges, especially for complex aromatic compounds such as PAH.s Electrokinetics (EK) is a remediation technology can be used to make species more accessible such as contaminants, nutrients, electrons acceptors, and electron donors. EK technology can be used to migrate certain contaminants but can also greatly enhance the aerobic degradation of PAHs primarily by increasing bioavailability and nutrient delivery. Studies were conducted to examine differences in electromigration rates for sand and clay. Two dyes, a red dye with anionic properties (FD&C 40) and a green dye with both anionic and cationic properties, composed of turmeric and Spirulina Blue were analyzed separately. The component of the green dye found to readily migrate is Spirulina Blue, consisting primarily of the protein pigment C-phycocyanin. The red dye in both sand and clay moves towards the anode, as predicted, and the rate between the two media was found to be approximately ten-fold. The green dye, having amphoteric qualities, can accept or donate protons, and can thus become strongly positively or negatively charged depending upon the pH of the system. It was found that due to a shifting pH gradient over time (in sand), this dye was initially anionic and thus migrated towards the anode but ceased migration after 48-72 hours due to a shift to a positive charge. Additional studies were conducted to observe how pH gradients in both sand and soil change over time. It is discovered that the rate at which the pH changes is dependent upon system variables including the current applied, which appears to absent from the literature, and that the initial semi-linear trend does not match the final gradient typically reported. The final study investigates the potential of EK technology to enhance biodegradation. In order to do so, a sandy soil, spiked with three compounds (fluorene, phenanthrene, fluoranthene) is placed within self-designed electrokinetic setups and an initial experiment shows a high possibility of PAH degradation but is unconfirmable. A second experiment attempts to verify the general findings of the first experiment and employs the use of a surfactant (Brij-35), which is thought to increase microbial movement throughout the contaminated soil and possibly reduce the sorption of PAHs to soil particles, both thereby increasing bioavailability and degradation rates. While biological activity is very apparent in this experiment, no degradation is observed and this may be due to a presence of carbonaceous materials (i.e. organic matter) within the soil. This yields an additional variable that must be taken into consideration in future in-situ studies or remediation projects. Overall it is found that many factors need to be taken into consideration for both aerobic and anaerobic biodegradation of PAHs. Increasing favorable growth conditions and increasing bioavailability can greatly help with this endeavor. Electrokinetics is an efficient means of ensuring this takes place but very specific designs or methods may be needed and pH gradients and extremes are found to provide significant obstacles to certain implementation but the results found in these experiments may be helpful to shed light on means of maintaining biological or chemical degradation experiments in an in-situ environment

Polycyclic Aromatic Hydrocarbons (PAHs) iIn the Diep And Plankenburg Rivers and potential remediation using charred Vitis vinifera (GRAPE) leaf litter

Thesis (DPhil (Chemistry))--Cape Peninsula University of Technology, 2019Occurrence of polycyclic aromatic hydrocarbons (PAHs) in freshwater systems may aggravate the water crisis currently being experienced in the Western Cape province of South Africa. However, there is dearth of data on the levels of PAHs, necessary for effective assessment of water quality as well as remediation strategies. This study therefore assessed levels of PAHs in two important freshwater systems in the Western Cape Province, South Africa. The potential of grape leaf litter for PAH abatement was also investigated. A solid-phase extraction - gas chromatography - flame ionisation detection (SPE-GC-FID) method was developed to simultaneously determine the 16 United States Environmental Protection Agency (US EPA) priority PAHs in environmental samples. Levels of 16 US EPA priority PAHs were assessed in water, sediment and plants from seven selected sites on the Diep and Plankenburg Rivers. Seasonal variations of some water quality parameters and PAHs levels in water and sediment samples were determined from the selected sites. Activated carbons produced from Vitis vinifera (grape) leaf litter were utilised for PAH-remediation. The SPE-GC-FID method developed for the 16 US EPA priority PAHs determination gave acceptable linearity (R2 > 0.999). Instrument detection limits ranged between 0.02 and 0.04 µg/mL and instrument quantification limits of between 0.06 and 0.13 µg/mL. Recovery studies were also acceptable (70.35 - 100.83%) with the exception of naphthalene that had lower recoveries. The average ∑16 PAHs detected in water samples at a given site, over a one-year period ranged from 73.90 to187.11 µg/L. The highest PAHs levels were detected in water samples from industrial areas of both rivers; chrysene (Chy) followed by benzo[a]anthracene (BaA) were the most abundant PAHs detected in water samples. Higher PAHs levels were detected in sediment samples relative to water samples; the average ∑16 PAHs detected in sediment samples at a given site, over a one-year period ranged from 6.048 to 39.656 µg/g. PAHs levels were also highest in sediment samples from industrial areas of the two rivers; benzo[b]fluoranthene (BbF) followed by benzo[k]fluoranthene (BkF) were the most abundant PAHs detected in sediment samples. The average ∑16 PAHs detected in plant samples [Phragmites australis (common reed) and Eichhornia crassipes (water hyacinth)] at a given site, ranged between 62.11 and 226.72 µg/g. Highest levels of PAHs were therefore detected in plant samples, suggesting possible bioaccumulation of PAHs in plant tissues. The bioaccumulation of PAHs by the plants also indicates the phytoremediation potential of these plants for PAHs remediation. The levels of PAHs measured in water and sediment samples were subjected to probabilistic risk assessment to predict the possibility of regulatory values being exceeded. The average percentage exceedence of 63.26 and 42.81 were obtained for PAHs in water samples of the Diep and Plankenburg Rivers respectively, while the corresponding average percentage exceedence obtained for sediment samples were 63.71 and 77.20. Vitis vinifera (grape) leaf litter showed enormous prospect as precursor for activated carbon. The yield of activated carbons obtained from grape leaf litter ranged from 44.65 to 58.40% and the Brunauer-Emmett-Teller (BET) surface area of up to 616.60 m2/g was obtained for activated carbons. The estimated adsorption capacities of the ZnCl2 and H3PO4 activated carbons for phenanthrene removal from aqueous solutions were 94.12 and 89.13 mg/g respectively. The environmental samples analysed were heavily contaminated with the 16 US EPA priority PAHs and the probabilistic risk assessment suggested risks of the carcinogenic PAHs at the levels measured in the environment. Vitis vinifera leaf litter, showed enormous potential as renewable precursor for activated carbon production, capable of removing varied contaminants from wastewater

Investigating the effects of plants and their root exudates on PAHs bioaccessibility to soil microorganisms and their impact on aged-contaminated brownfields remediation.

In Wallonia, there are 6,000 estimated brownfields (rising to over 3.5 million in Europe) that require remediation. Polycyclic aromatic hydrocarbons (PAHs) are persistent organic compounds of major concern that tend to accumulate in the environment, threatening ecosystems and health. They represent 17% of all encountered pollutants. The thesis, articulated around several axes, focused on improving less aggressive PAHs remediation techniques in brownfields, such as bioremediation and phytoremediation, as alternatives to environmentally aggressive, expensive and often disruptive current soil remediation strategies. More specifically, it was built on several authors' observation that PAHs soil contents decrease in the presence of plants. The hypothesis was made that this could be related to the production of plant root exudates. A bioaccessibility measurement protocol was adapted to two brownfield soils using Tenax® beads in order to compare PAHs bioaccessibility in soil samples. In both experimental soils, PAHs desorption kinetics were established, described by site distribution models, and common extraction times were calculated (respectively 48 h and 24 h for both experimental soils). The potential of saponin (a natural surfactant) as extracting agent and as a bioremediation enhancer on an aged-contaminated soil was investigated. In a first experiment, soil samples were extracted with saponin solutions (0; 1; 2; 4 and 8 g L-1). In a second experiment conducted in microcosms (28°C), soil samples were incubated for 14 or 28 days in presence of saponin (0; 2.5 and 5 mg g-1 DW). CO2 emissions were monitored throughout the experiment. After the incubation, dehydrogenase activity was measured as an indicator of microbiological activity, and the bioaccessible and residual PAHs contents were determined. The 4 g L-1 saponin solution globally extracted significantly more PAHs than water. Neither PAHs dissipation nor bioaccessibility were enhanced in presence of saponin compared to control samples after 28 days. However, CO2 emissions and dehydrogenase activities were significantly more important in presence of saponin, suggesting no toxic effect of this surfactant towards soil microbiota. The role of two Fabaceae (Medicago sativa L. or Trifolium pratense L.) root exudates in enhancing PAHs bioaccessibility and dissipation in an aged-contaminated soil was investigated during an incubation experiment (28°C). The CO2 emissions were significantly higher in presence of T. pratense exudates; the dehydrogenase activities (measured after 14 and 28 days) showed improvements of the soil microbial activity in presence of both types of root exudates compared to untreated soil samples; the PAHs residual contents decreased more in untreated samples than in the presence of T. pratense exudates; and M. sativa exudates lowered PAHs bioaccessibility but not residual contents. The effects of Medicago sativa L. and Trifolium pratense L. on the PAHs’ bioaccessibility and dissipation in an aged-contaminated soil throughout a rhizoremediation trial were investigated. The bioaccessible and residual PAH contents were quantified after three, six and twelve months of culture. The rhizoremediation results show that M. sativa developed better than T. pratense on the contaminated soil. When plants were absent (control) or small (T. pratense), the global PAHs’ residual contents dissipated from the rhizosphere to 8% and 10% of the total initial content, respectively; in the presence of M. sativa, dissipation after 12 months was only 50% of the total initial content; and the PAHs bioaccessible content increased more significantly in the absence of plants. Finally, a review of three scientific trends that lead PAHs contaminated soils/sediments remediation studies and management was conducted. (i) The choice of PAHs compounds that are being studied and targeted in scientific literature were discussed, and it was suggested that the classical 16 PAHs from the American Environmental Protection Agency’s (US-EPA) watch list might no longer be sufficient to meet actual environmental challenges. (ii) The choice of experimental material in remediation studies was discussed. Bibliometric measures were used to show the lack of PAHs remediation trials based on co-contaminated or aged-contaminated material. (iii) The systematic use of the recently validated bioaccessibility measurement protocol (ISO/TS 16751:2018) in remediation trials was discussed, and it was suggested that such measurement should be implemented as a tool to improve remediation processes and management strategies

Bioavailability and biodegradation of polycyclic aromatic hydrocarbons

One of the main problems in biological soil remediation is the slow or incomplete degradation of hydrophobic organic pollutants. The principal reason for this problem is the fact that these compounds bind strongly to the soil matrix or occur as a separate non- aqueous phase in the soil. As most microbiological processes take place in the water phase, transport of the polluting compound to this phase is essential for biodegradation to occur. When this transport is the limiting factor in the biodegradation process, this is termed limiting bioavailbility.This thesis deals with the effect of bioavailability on the biodegradation of polycyclic aromatic hydrocarbons (PAHs). PAHs are hydrophobic organic pollutancs that are abundantly present in contaminated soils and give raise to ervironmental concern because of their toxicity and mutagenicity. Most PAHs are degradable by microorganisms and the important biochemical aspects of the PAH-degradation hav been revealed. PAHs are nevertheless considered persistent pollutants in soil, a fac that is attributed to their limited bioavailability.The first part of the research consisted of the isolation of bacteria capable of degrading the PAHs, naphthalene, phenanthrene, and anthracene. Subsequently a number of isolated bacterial strains were grown in batch and continuous cultures to determine the most important microbial growth parameters, such as the maximum growth rate, the Monod saturation constant, and the bacterial growth yield.The effect of bioavailability on the biodegradation of PAHs was studied in two model systems: (i) crystalline PAHs and (ii) PAHs bound to a matrix.For studying the bioavailability of crystalline PAHs the results of dissolution and biodegradation experiments were compared. In the degradation experiments it was found that two phases could be observed during batch growth: an exponential growth phase, followed by a linear growth phase, in which biomass formation was limited by the availability of the PAHs. By using a model in which Monod kinetics for bacterial growth were coupled to dissolution kinetics for substrate availability, it was shown that the observed degradation rates were matched by the rates of dissolution of the PAHs to the aqueous phase. Therefore it was concluded that in this system only aqueous phase PAHs were available for bacterial uptake and that the bioavailability of the PAHs was not directly stimulated by the presence of the microorganisms.With matrix-bound PAHs desorption and biodegradation experiments were conducted. The first matrices studied were the synthetic porous resins XAD4 and XAD-7. The desorption of naphthalene from these materials was studied in batch and continuous desorption experiments. The results from these experiments could be described using a two-compartment model in which the matrix is divided in a fraction with shallow pores and one with deep pores. In biodegradation experiments with naphthalene- loaded resins the same type of batch-growth kinetics was observed as described above for crystalline substrates: exponential growth, followed by a phase in which substrate availability limits the degradation rate. By comparing the results of the desorption experiments and the biodegradation experiments it was shown that the biodegradation proceeded faster than could be explained by desorption alone. Therefore it was concluded that the bacteria had a positive effect on the bioavailability of naphthalene that was adsorbed onto the resins. This effect was not caused by the presence of bacterial excretion products.In contrast to this it was found that the biodegradation of soil-bound naphthalene and phenanthrene could be explained by degradation of PAHs present in the aqueous bulk phase only. Thus, the bioavailability of sorbed PAHs depends on the type of matrix the PAHs are sorbed onto.The second part of this thesis deals with the most widely applied solution for the problem of limited bioavailability: the application of surface-active agents or surfactants. Surfactants are molecules that usually consist of a hydrophillic and a hydrophobic part. Due to this they have a tendency to concentrate at surfaces and interfaces and to form new interfaces. There are several different ways by which surfactants may increase the bioavailability of hydrophobic compounds in soil:- solubilization in the aqueous phase by the presence of micelles, aggregates of 20-200 surfactant molecules with a hydrophobic interior;- emulsification of liquid hydrocarbons in the waterphase;- facilitated transport, a term that covers several processes, such as mobilisation of pollutant present in soil pores or interaction pollutant with single surfactant molecules;Surfactants may also have a negative effect on pollutant bioavailability, for instance by the toxic effect or preferential degradation of the surfactant, or by interference with the natural interactions among microorganisms and pollutant.The effect of several nonionic surfactants on the bioavailability of PAHs was studied in the same model systems as described above: crystalline PAHs and PAHs sorbed onto a matrix.Dissolution experiments with crystalline naphthalene and phenanthrene showed that the presence of surfactants caused an increase in the apparent solubility and in the maximum dissolution rate of these PAHs. Both phenomena have an effect on the bioavailability of PAHs. Although it was found that micellar PAHs were not readily available for uptake by the bacteria, the transport of PAHs from the micelles is sufficiently fast to allow almost complete exponential growth on solubilized PAHs. The effect on the maximum dissolution rate is probably more important because this is the most relevant factor under bioavailability-limiting conditions. Addition of surfactant to cultures growing on PAH in the dissolution-limited phase resulted in an increase in the linear growth rate. This shows that for crystalline PAHs surfactants can be used to increase the bioavailabiltyFor sorbed naphthalene similar results were found. In desorption experiments it was shown that in the presence of surfactant, the partitioning of naphthalene to the waterphase as well as the maximum desorption rate was increased. Addition of surfactants to cultures growing on sorbed naphthalene in the desorption-limited phase resulted in an increase in the degradation rate. This shows that surfactants can be used for enhancing the bioavailability of sorbed PAHs.The first general conclusion from this thesis is that the bioavailability of hydrophobic pollutants in soil is a complex matter and therefore difficult to quantify. In model systems under laboratory conditions, however, it was possible to simulate the essential processes. This experimental work revealed the most important mechanisms that play a role in bioavailability limtations. Because of the large impact of bioavailability on both the performance of biological soil remediation and on the risks posed by soil contamination, it is essential that standard methods be developed which provide criteria for bioavailability. These criteria may be used to predict the results of biological soil remediation processes and may form a basis for soil quality limits in which the bioavailability of the pollutant is considered.Secondly, the application of surfactants can be concluded to be a promising option for enhancing the bioavailability of hydrophobic pollutants. In two model sytems it was shown that addition of surfactants speeded up the biological degradation of PAHs markedly and some explanations for this phenomenon have been found. However, to allow the use of surfactants as a standard technique in biological soil remediation, more insight into the complex interactions involved in the introduction of surfactants into soil is necessary

Effects of surfactants and Fenton\u27s reagents on extraction and destruction of phenanthrene in spiked sand

In this study, surfactants and Fenton\u27s reagents (Fe(II) and H202) ere proposed to solve contaminated site problems in situ on a lab scale. Phenanthrene is a simple PAHs (polynuclear aromatic hydrocarbons). The phenanthrene spiked ottawa sand simulated contaminated soil. HPLC was used for phenanthrene analysis because it provided excellent separation and no interference. Six surfactants (including nonionic and ionic) were tested. The operating conditions were optimized based on process and economic considerations such as reaction time, mixing speed, concentrations of surfactants and concentrations of Fenton\u27s reagents. Surfactants could effectively dissolve phenanthrene from the spiked sand. In the absence of surfactants, Fenton\u27s reactions could efficiently decompose the target compound on the sand surface. Running a sequence of Fenton\u27s reactions was more effective than a single reaction. The combinations of a surfactant and Fenton\u27s reaction were better than the effect of a surfactant only. A model was developed that can qualitatively predict the residual phenanthrene concentration on sand surface as a function of time, mixing speed and concentrations of surfactant and Fenton\u27s reagents. The model was in excellent agreement with the experimental results

The impact of nutrient and biodiesel amendments on the biodegradation of hydrocarbons in contaminated soil

PhD ThesisThe effect of nutrient, biodiesel and biochar amendments on the biodegradation of pollutant hydrocarbons was investigated in soil spiked with crude oil and coal tar over periods of up to 180 days. Biodiesel was chosen as an amendment for increasing the bioavailability of hydrocarbon pollutants because of its good solvent properties but low toxicity. Results from laboratory microcosm experiments on soil spiked with weathered and un-weathered tar showed that after 60 days, the concentrations of the potent carcinogen benzo[a]pyrene (BaP) were significantly reduced by 92 and 81%, respectively, in the biodiesel amended samples compared to the 17 and 26% reduction in the controls, and 8 and 34% depletion observed in the nutrient-only amended microcosms, respectively. The 3-ring PAH anthracene was also almost completely biodegraded in all the biodiesel amended experiments. However, phenanthrene degradation was significantly inhibited in these samples as only 0-2% reduction occurred after 180 days as opposed to the losses (>70%) observed in the control and the nutrient amended experiments. Apparent increases in concentrations were observed for some 4-ring PAHs, while the degradation of other 5 and 6-ring compounds was enhanced in the biodiesel amended samples probably due to their increased solubilisation by biodiesel. A stepwise treatment approach conducted on tar spiked soil revealed a higher reduction in BaP (98%) in the biodiesel amended microcosms compared to the control (29%) and phenanthrene depletion was also enhanced by 51% after 60 days of adding biodiesel to soil initially treated with nutrients. A similar trend in PAH degradation was observed for the crude oil spiked soil, but in these experiments the removal of the n-alkanes was significantly enhanced by nutrient amendment alone, while degradation of the branched alkanes was increased in the biodiesel treatments. Toxicity assays showed that biodiesel amended microcosms stimulated phosphatase enzyme activity and exhibited a lower toxic response to Microtox Vibrio fischeri. In this study, biochar amendment did not significantly reduce residual pollutant concentrations. Overall, the pattern observed in the removal of the PAHs using biodiesel, suggests the cometabolic action of ligninolytic fungi, probably via lignin peroxidases, as also evidenced from the visible growth of moulds after 7-14 days of amendment. The enhanced removal of carcinogenic PAH and the reduced toxicity observed in soil after biodiesel amendment, indicates that this bioremediation technique has potential for full scale field trials.Petroleum Technology Development Fund (PTDF) Scholarship Scheme, Nigeri

Develop a multi-functional green pervious concrete (MGPC) pavement with polycyclic aromatic hydrocarbons (PAHs) removal function.

Stormwater runoff induced Polycyclic Aromatic Hydrocarbons (PAHs) contaminant increasingly imperils the groundwater quality and the sustainable development of human society due to the potential carcinogenic risks. Pavement can be considered as the first line of defense for contaminant removal of the stormwater runoff. New construction materials with stormwater runoff quantity and quality control are in urgent demand for updating the existing pavement system. An innovative material called Multi-functional Green Pervious Concrete (MGPC) was developed in the department of Civil and Environmental Engineering at University of Louisville. This material uses organoclay as the amendment to enhance the PAHs removal capacity of conventional pervious concrete. The objective of this study is to evaluate the potential implementation of MGPC as a pavement material with the groundwater contamination remediation functions. The study was performed in five stages. First, The PAHs remediation function of MGPC was tested by introducing organoclay [bis (hydrogenated tallow alkyl) dimethyl ammonium modified montmorillonite] to the conventional pervious concrete. After test and verification, the mix proportion of MGPC was designed to meet the compressive strength and hydraulic conductivity requirements of pervious concrete. A small amount of organoclay addition was found not to adversely affect the compressive strength and hydraulic conductivity of MGPC. The preliminary study of the PAHs removal functions of MGPC was conducted in stage two. The isothermal batch sorption test was conducted to quantify the sorption capacity of the organoclay modified cement paste, and the column test was performed to investigate the transport mechanism and retardation behavior of PAHs in MGPC. It was found that the developed MGPC with a small addition of organoclay could substantially remove PAHs contaminants and it also has much stronger adsorption and retardation capacity than the conventional pervious concrete. In stage three, a series of comprehensive laboratory-scale tests were conducted to examine the effectiveness of stormwater induced PAHs removal by using the MGPC pavement. The results indicated that the initial concentrations of the PAHs and the flow rates would impact the removal efficiency of MGPC. The tests showed that the MGPC still maintained considerable sorption capacity after 50 PAHs sorption and desorption cycles. An ideal site under steady-state groundwater conditions was generated to simulate the long-term performance of MGPC on PAHs removal by using the finite element method in stage four. The laboratory experiments were used to determine the physicochemical parameters of MGPC, and three sorption isothermal models (linear, Freundlich and Langmuir) were fitted to the sorption test data. The computer simulation revealed that the MGPC had significant remediation efficiency on the PAHs contaminant. Other than the material properties of MGPC, the efficiency of contaminant remediation of MGPC was also found to be influenced by the permeability of the subbase and the initial concentration of PAHs. It was also found that the linear isotherm model would overestimate the removal efficiency of PAHs with higher concentration sources. At last final fifth stage, a Pavement Environment and Performance Index (PEPI) was proposed to evaluate the environmental impacts of three different types of pavements (impervious concrete, conventional pervious concrete, and MGPC). The data from experiments and the Environmental Footprint Database was used to calculate the PEPI. Based on the Life Cycle Assessment (LCA) results, it was found that the MGPC pavement was much more environmentally friendly with relatively lower greenhouse gas emissions and energy consumption, and better environmental performance comparing with the other two types of pavements

Statistical optimization and kinetic studies of enhanced bioremediation of crude oil - contaminated marine water using combined adsorption-biostimulation strategy

The objectives of this study were to investigate and evaluate through Taguchi orthogonal experimental design the effects of amendment agents as well as the optimization and kinetics of enhanced bioremediation of crude oil-contaminated marine water using combined adsorption-biostimulation strategy. The amendment agents are organic fertilizer, slow release inorganic NPK fertilizer, commercial activated carbon and Tween 80. Bioremediation of weathered Escravos crude oil (WECO)-contaminated marine water was studied for four weeks in ten plastic buckets open system. The oil-contaminated marine water in nine of the buckets was each amended with the amendment agents according to Taguchi’s (L9) orthogonal array of four factors and three levels and the tenth un-amended bucket served as control (natural bioattenuation). Results showed that the amendment agents had relative significant influence on the enhancement of WECO-marine water bioremediation. The optimum amendment agent conditions were determined as follows: organic fertilizer 30 g, inorganic slow release NPK fertilizer 4 g, activated carbon 30 g, and Tween 80, 1.5 g. Under these optimum conditions, the optimum percentage of crude oil biodegradation achieved was 98.25%. Bioremediation kinetic data of WECO fitted well to the first-order kinetic model. The combined adsorptionbiostimulation strategy (using the amendment agents) resulted in higher biodegradation rate constant, k (0.0443 - 0.1183 day-1) and lower biodegradation half-life,  t1/2 (5.86 – 15.6 days) of the WECO biodegradation than the natural bioattenuation with lower k (0.0144 day-1) and higher t1/2 (48.8 days). Therefore, the amendment agents have effective potential application as a tool for combined adsorption-biostimulation strategy in the remediation of crude oilcontaminated aquatic environment.Keywords: Biodegradation; Bioremediation; Amendment agents; Crude oil; Kinetics; Optimizatio

Comparative effects of several cyclodextrins on the extraction of PAHs from an aged contaminated soil

7 páginas.-- 3 figuras.-- 2 tablas.-- 52 referencias.-- Supplementary dataThe objective of the present study was to characterise the polycyclic aromatic hydrocarbons (PAHs) content of an aged contaminated soil and to propose remediation techniques using cyclodextrins (CDs). Four CDs solutions were tested as soil decontamination tool and proved more efficient in extracting PAHs than when an aqueous solution was used; especially two chemically modified CDs resulted in higher extraction percentages than natural β-CD. The highest extraction percentages were obtained for 3-ring PAHs, because of the appropriate size and shape of these compounds relative to those of the hydrophobic cavities of the CDs studied. A detailed mechanistic interpretation of the chemical modification of CDs on the extraction of the different PAHs has been performed, and connected with the role that the different hydrophobicities of the PAHs play in the extraction behaviour observed for the 16 PAHs, limiting their accessibility and the remaining risk of those PAHs not extractable by CDs. © 2013 Elsevier Ltd. All rights reserved.The authors thank to Dr. J.R. Gallego from the Universidad de Oviedo for providing the contaminated soil sample. Support from projects CTM2006-04626 and CTM2009-07335, Spanish Ministry of Science and Innovation (co-funded by Fondo Europeo de Desarrollo Regional, FEDER), are greatly appreciated. M.A. Sánchez-Trujillo acknowledges a research contract from CSIC (JAEPre 0800763) cofinanced by Fondo Social Europeo (FSE).Peer Reviewe