Treatment system for solid matrix contaminated with fluoranthene. II--Recirculating photodegradation technique.

A laboratory-scale solar reactor and photodegradation technique were developed to enhance the degradation process of fluoranthene. Fluoranthene was used in this study to represent toxic polycyclic aromatic hydrocarbons (PAHs) that are persistent in the environment. The extracted fluoranthene from soil in organic solvent (EFOS) and hydrogen peroxide (H2O2) were pumped from a 100 ml vessel into a solar glass cell coated with titanium dioxide (TiO2) at 80 microl min(-1). This work compares the efficiency of the developed photocatalytic degradation technique with the conventional batch process. The degradation efficiency of the developed technique was assessed at different initial concentrations of fluoranthene and percentages of H2O2 in the extract using different flow rates. Preliminary results indicated that the developed technique degraded 99% of fluoranthene from EFOS in the presence of H2O2 and 83% without H2O2. There was no significant difference between fluoranthene degradation rates by the developed technique and the batch method. The developed technique however, treated double the volume of solution that was treated by the batch reactor method which was time consuming and required continuous attention.     

Optimization of an effective extraction procedure for the analysis of microcystins in soils and lake sediments

Microcystin analysis in sediments and soils is considered very difficult due to low recovery for extraction. This is the primary limiting factor for understanding the fate of toxins in the interface between water and sediment in both the aquatic ecosystem as well as in soils. In the present study, a wide range of extraction solvents were evaluated over a wide range of pH, extraction approaches and equilibration time to optimize an effective extraction procedure for the analysis of microcystins in soils and lake sediments. The number of extractions required and acids in extraction solutions were also studied. In this procedure, EDTA-sodium pyrophosphate solution was selected as an extraction solvent based on the adsorption mechanism study. The optimized procedure proved to be highly efficient and achieved over 90% recovery. Finally, the developed procedure was applied to field soil and sediment sample collected from Chinese lakes during bloom seasons and microcystins were determined in six of ten samples.     

Effect of condensed organic matter on solvent extraction and aqueous leaching of polycyclic aromatic hydrocarbons in soils and sediments

The contents of nonhydrolyzable organic matter (NHC) and black carbon (BC) were measured in soils and sediments from the Pearl River Delta, South China. Polycyclic aromatic hydrocarbons (PAHs) were extracted respectively by Soxhlet and an accelerated solvent extraction device (ASE) using different solvents. In addition, sequential aqueous leaching at different temperatures was carried out. The PAH content extracted with the sequential three solvent ASE is two times higher than that using the Soxhlet extraction method. The relationship of the PAH content with the NHC content is very significant. The PAH concentrations measured at various temperature steps fit well to the Van't Hoff equation and the enthalpy was estimated. The investigation indicates that condensed organic matter such as kerogen carbon, aged organic matter, and BC is relevant for the extraction and distribution of native PAHs in the investigated field soils and sediments.     

Microtox testing of pentachlorophenol in soil extracts and quantification by capillary electrochromatography (CEC)--a rapid screening approach for contaminated land

An approach to rapid soil testing which involved the use of simple solvent extraction methods was developed. The analytes of interest were priority pollutants of low water solubility which could not be readily removed from the soil using water. Direct toxicity testing of the soil samples by Microtox showed a high background toxicity which prevented realistic toxicity data from being obtained for the contaminants present. A range of different extraction solutions was used in an attempt to extract the contaminants while eliminating the matrix effects of the soil. It was necessary that the solvents selected for extraction of the soil samples were not of significant toxicity, as this could potentially mask the toxic effects of any compounds extracted from the soil. The extraction efficiencies of solvent systems were evaluated using pentachlorophenol (PCP) as a model compound of known toxicity in the Microtox assay. A rapid and cost-effective method was developed in order to determine the amount of PCP recovered from the soil by the extraction solvents employed. This method consisted of a solid phase extraction (SPE) step followed by quantification using capillary electrochromatography (CEC). Recoveries were greater when a higher proportion of organic solvent (methanol) was used in the extraction process, and lowest when water was used. An extraction based on water could provide information on the potential for leaching of contaminants from the soil into nearby water bodies in an environmental setting. An organic solvent extraction method could indicate how much toxicity soil-dependent organisms might be exposed to through ingestion. Extraction based on 50% (v/v) methanol in water was considered to be the most suitable overall extraction solution for soil screening, given that this permitted extraction of the water-insoluble compound PCP at a level which was clearly toxic in the Microtox assay while also retaining the capability to extract water-soluble contaminants.     

Chemical assays of availability to earthworms of polycyclic aromatic hydrocarbons in soil

The bioavailable concentration of an organic pollutant is less than the concentration determined by vigorous extraction of soil. Because bioavailability varies with the particular compound, soil, and aging time, an assay for bioavailability is needed. Three methods were tested: extraction with a 25% aqueous solution of tetrahydrofuran (THF), 95% ethanol, and C18 membranes. Evaluations were conducted with a mixture of four polycyclic aromatic hydrocarbons (PAHs) added to five dissimilar soils and with pyrene as sole PAH added to six soils, and the availability of aged and freshly added compounds was determined. Assimilation by earthworms (Eisenia fetida) was used to assess bioavailability. For extraction with THF and earthworm uptake, the correlation coefficients of determination (R2) for anthracene, chrysene, pyrene, and benzo(a)pyrene added as a mixture exceeded 0.85. The R2 values for assays with the C18 membrane were 0.77 or higher. The values for pyrene added alone were 0.710 and 0.823, respectively. R2 values for assays with ethanol often exceeded 0.87, but lower values were sometimes obtained. We suggest that such solvent or solid-phase extractions may be useful in assessing PAH bioavailability.     

Solvent extraction for heavy crude oil removal from contaminated soils

A new strategy of heavy crude oil removal from contaminated soils was studied. The hexane-acetone solvent mixture was used to investigate the ability of solvent extraction technique for cleaning up soils under various extraction conditions. The mixtures of hexane and acetone (25 vol%) were demonstrated to be the most effective in removing petroleum hydrocarbons from contaminated soils and approx 90% of saturates, naphthene aromatics, polar aromatics, and 60% of nC₇-asphaltenes were removed. Kinetic experiments demonstrated that the equilibrium was reached in 5 min and the majority of the oil pollutants were removed within 0.5 min. The effect of the ratio between solvent and soil on the extraction efficiency was also studied and results showed that the efficiency would increase following the higher solvent soil ratio. Then the multistage continuous extraction was considered to enhance the removal efficiency of oil pollutants. Three stages crosscurrent and countercurrent solvent extraction with the solvent soil ratio 6:1 removed 97% oil contaminants from soil. Clearly the results showed that the mixed-solvent of hexane and acetone (25 vol%) with character of low-toxic, acceptable cost and high efficiency was promising in solvent extraction to remove heavy oil fractions as well as petroleum hydrocarbons from contaminated soils.     

Solvent Extraction Processes: A Survey of Systems in the SITE Program

Solvent extraction of contaminated soils, sludges and sediments has been successfully completed at a number of Superfund sites. Each commercialized process uses a unique operating system to extract organic contaminants from solids. These operating systems may be classified by the properties of the solvents each utilizes: (1) standard solvents, (2) near-critical fluids/liquified gases, and (3) critical solution temperature solvents. Pretreatment and post-treatment requirements vary depending upon the operating systems of the solvent extraction system. Future demonstrations of these technologies by the U.S. EPA’s Superfund Innovative Technology Evaluation Program will provide additional information regarding the efficacy of these processes.     

Solvent extraction and tandem dechlorination for decontamination of soil

The United States Environmental Protection Agency (US EPA) guidelines allow removal of polychlorinated biphenyls (PCBs) from soils via solvent extraction. This option holds promise for removal of other recalcitrant organic contaminants as well. A study was undertaken to evaluate the effectiveness of solvent extraction with two tandem degradation techniques. The degradation techniques were chemical dehalogenation with immobilized reagents and gamma-ray irradiation. The integrated approach was evaluated with contaminated soils from wood treatment and electric power substation sites. Evaluations were carried out on a bench scale in the laboratory and on a semi-pilot scale at a contaminated site. Binary solvent mixture of alkanes and alcohols yielded the highest extraction efficiencies. Extraction efficiencies in excess of 90% were obtained for PCBs, polychlorinated dibenzo-p-dioxins (PCDDs) and polynuclear aromatic hydrocarbons (PAHs). Extracted PCBs were rapidly degraded through chemical dehalogenation or with high doses of the gamma-ray irradiation. The residual organics in the solvent mixture were removed with activated carbon, and the solvent was recycled for subsequent soil extractions. Contaminants adsorbed on the activated carbon were destroyed with a counter flow oxidation process.     

Scavenging of BHCs and DDTs from soil by thermal desorption and solvent washing

Intensive remediation of abandoned former organochlorine pesticides (OCPs) manufacturing areas is necessary because the central and surrounding soils contaminated by OCPs are harmful to crop production and food safety. Organochlorine and its residues are persistent in environments and difficult to remove from contaminated soils due to their low solubility and higher sorption to the soils. We performed a comprehensive study on the remediation of OCPs-contaminated soils using thermal desorption technique and solvent washing approaches. The tested soil was thermally treated at 225, 325, 400, and 500 °C for 10, 20, 30, 45, 60, and 90 min, respectively. In addition, we tested soil washing with several organic solvents including n-alcohols and surfactants. The optimal ratio of soil/solvent was tested, and the recycling of used ethanol was investigated. Finally, activities of polyphenol oxidase (PPO), urease (URE), alkaline phosphatase, acid phosphatase (ACP), and invertase (INV) were assayed in the treated soils. The tested soil was thermally treated at 500 °C for 30 min, and the concentration of contaminants in soil was decreased from 3,115.77 to 0.33 mg kg^?1. The thermal desorption in soil was governed by the first-order kinetics model. For the chemical washing experiment, ethanol showed a higher efficiency than any other solvent. Using a 1:20 ratio of soil/solvent, the maximum removal of OCPs was achieved within 15 min. Under this condition, approximately 87 % of OCPs was removed from the soils. More than 90 % of ethanol in the spent wash fluid could be recovered. Activities of some enzymes in soils were increased after ethanol treatment. But ALP, ACP, and INV activities were decreased and PPO and URE showed slightly higher activities following remediation by thermal treatment. Both heating temperature and time were the key factors for thermal desorption of OCPs. The n-alcohol solvent showed higher removal of OCPs from soils than surfactants. The highly efficient removal of OCPs from soil was achieved using ethanol. More than 90 % of ethanol could be recovered and be reused following distillation. This study provides a cost-effective and highly efficient way to remediate the OCPs-contaminated soils.     

Removal of PCBs from a Contaminated Soil Using CF-Systems® Solvent Extraction Process

ABSTRACT

The U.S. Environmental Protection Agency’s (EPA) Superfund Technical Assistance Response Team (START) in cooperation with EPA’s Superfund Innovative Technology Evaluation (SITE) program evaluated a pilot scale solvent extraction process developed by CF-Systems. This process uses liquefied propane to extract organic contaminants from soils, sludges, and sediments. A pilot-scale evaluation was conducted in Golden, CO at Hazen Research, Inc., using CF-Systems’ trailer-mounted organics extraction unit. Approximately 1,000 pounds of soil, with an average poly-chlorinated biphenyl (PCB) concentration of 260 mg/kg, was obtained from a remote Superfund site. Six 100-pound batches of the contaminated soil were extracted using multiple extraction sequences. Three of the six batch runs were subjected to three extraction sequences each, so that process variability could be evaluated. Results showed that PCB removal efficiencies varied between 91.4 and 99.4%, with the propane-extracted soils retaining low concentrations of PCBs (19.0–1.8 mg/kg). Removal efficiencies of oil and grease (O&G) were found to be 96.0 to 99.6% with propane-extracted soils retaining O&G concentrations from 279 to <20 mg/kg. Overall extraction efficiency was found to be dependant upon the numberof extraction cycles used.     

Comparative study of extraction methods for the determination of PAHs from contaminated soils and sediments

The following four methods were compared on the extraction efficiency of 16 EPA (US Environmental Protection Agency) polycyclic aromatic hydrocarbons (PAHs): German method of the Verband Deutscher Landwirtschaftlicher Untersuchungs und Forschungsanstalten (VDLUFA), two methods of the International Organization for Standardization using shaking (ISO A) and Soxhlet extraction (ISO B) and an ultrasonic method. Recovery rates of 16 PAHs were determined in two soils. Extraction efficiency was evaluated in five soils and three sediments. Effect of drying soils and sediments on extraction efficiency was tested using the VDLUFA and the ultrasonic methods. Our study shows that the number of aromatic rings, rather than extraction procedures, significantly influenced recovery rates of individual PAHs. No significant differences in extraction efficiency of the four methods were observed for less polluted samples. For highly polluted soils, extraction efficiency decreased in the following order: VDLUFA method > ISO A > ultrasonic method > ISO B. Influence of soil moisture on extraction efficiency depended to some extent on both solvent used and content of PAHs in samples. A mixture of dichloromethane/acetone (5:1) is recommended for PAH extraction from moist samples when the ultrasonic method is used.     

Remediation of contaminated soil by a solvent/surfactant system

This study investigates a new approach using a solvent/surfactant-aided soil-washing process to improve the performance of conventional surfactant-aided soil remediation. Three surfactants (Brij 35, Tween 80, and SDS) and three organic solvents (acetone, triethylamine, and squalane) were used to evaluate the desorption performances of 4,4'-dichlorobiphenyl (DCB) out of three soils with different sorption characteristics. The performance improvement is likely due to better dissolution of the hydrophobic contaminants from the soil assisted by the solvent, and the formation of solvent-incorporated surfactant micelles, which increases both the size (i.e. capacity) and affinity of micelles for more effective contaminant extraction. The foc of soils were found to be important in determining the performance of a solvent/surfactant-aided soil-washing process. Judging from the experimental data and as verified by the two constants in the proposed soil-washing model, as the organic solvent is coexisting with the surfactant micelles, both the marginal soil-washing performance (right after the use of a very small amount of solvent compared to that of none) and the final soil-washing capacity are increased compared to those of a pure surfactant-aided washing process.     

Scaling up a treatment to simultaneously remove persistent organic pollutants and heavy metals from contaminated soils

Soil washing is a treatment process that can be used to remediate both organic and inorganic pollutants from contaminated soils, sludges, and sediments. A soil washing procedure was evaluated utilizing about 100 g samples of soil that had been field-contaminated with arsenic, chromium, copper, pentachlorophenol (PCP), polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). The highest level of mobilization/detoxification was achieved in three soil washes with a mixture of 0.1M [S,S]-ethyelnediaminedisuccinate ([S,S]-EDDS) and 2% Brij 98 at pH 9 with 20 min of ultrasonication treatment at room temperature. This combination mobilized 70% of arsenic, 75% of chromium, 80% of copper, 90% of PCP, and 79% of PCDDs and PCDFs, so that the decontaminated soil met the maximum acceptable concentrations of the generic C-level criteria regulated by the Ministère du Développement Durable, de l’Environnement et des Parcs for the Province of Québec, Canada.The organic pollutants were back-extracted from the aqueous suspension with hexane. Heavy metals were virtually completely precipitated from the aqueous washing suspension with Mg⁰ particles at room temperature. The PCP was detoxified by catalytic hydrodechlorination with a stream of 5% (v/v) H₂-supercritical CO₂ that transported the organosoluble fraction through a reaction chamber containing 2% Pd/γ-Al₂O₃.In toto, this soil washing procedure demonstrates that persistent organic pollutants and selected heavy metals can be co-extracted efficiently from a field-contaminated soil with three successive washes with the same soil washing solution containing [S,S]-EDDS and a non-ionic surfactant (Brij 98) in admixture. An industrial-scale ex situ soil washing procedure with a combination of a non-ionic surfactant and a complexing reagent seems to be a plausible remediation technique for this former wooden utility pole storage facility.     

Study of factors affecting on the extraction efficiency of polycyclic aromatic hydrocarbons from soils using open-vessel focused microwave-assisted extraction

As part of an evaluation of focused microwave-assisted extraction (FMAE) using an open-vessel system, the effects of matrix, moisture content, ageing, and solvent have been studied on the extraction efficiency of polycyclic aromatic hydrocarbons (PAHs) from spiked soils. PAHs were spiked onto three different uncontaminated air dried and originally wet soil matrices with 1- and 20-day ageing periods. Solvents used were hexane–acetone (1:1), cyclohexane–acetone (1:1) and dichloromethane. FMAE only required a small amount of solvent (20 ml) and short extraction time (10 min) in the open cell under 90 W of microwave power. The results revealed that the extraction efficiency strongly depends on the nature of soil matrix; moisture content may enhance the recoveries of PAHs for many cases; and, the influence of the type of solvent is not significant. A comparison between microwave extraction and 16-h Soxhlet extraction has been made on spiked soils. It evidenced that the microwave method under ambient pressure is a suitable alternative to Soxhlet method for the analysis of PAHs in soils. For the evaluation of the developed FMAE method, three reference materials were used. The PAHs recovered from three reference materials were in a good agreement with reference values.     

Optimizing microwave-assisted solvent extraction (MASE) of pesticides from soil

Microwave-assisted solvent extraction (MASE) was investigated as an alternative for extraction of parathion (O,O-diethyl O-4-nitrophenyl phosphorothioate), methyl parathion (O,O-dimethyl O-4-nitrophenyl phosphorothioate), p,p'-DDE [1,1'-dichloro-2,2-bis(4-chlorophenyl)ethane], hexachlorobenzene (HCB), simazine (6-chloro-N2,N4-diethyl- 1 ,3,5-triazine-2,4-diamine) and paraquat dichoride (1,1'-dimethyl-4,4'-bipyridinium) from two different soils and from an earthworm-growing substrate. The matrices were fortified with 14C-radiolabeled pesticides and extracted with various solvent systems under different microwave conditions. Recoveries of more than 80% could be obtained depending on the used microwave conditions and solvent, except for paraquat whose recovery was generally less efficient. Thus, MASE can be successfully used to extract pesticides from environmental and biological samples and could be a viable alternative to conventional extraction methods. The technique uses smaller amounts of organic solvents, thereby minimizing the costs of the analysis and the disposal of waste solvent.     

A comparative study on the recovery of polycyclic aromatic hydrocarbons from fly ash and lignite coal

The recovery of polycyclic aromatic hydrocarbons (PAHs) from lignite coal burnt in Greek power stations and the fly ash produced is examined comparatively using Soxhlet, ultrasonic and accelerated solvent extraction procedures with various organic solvents. Soxhlet using toluene/methanol mixture and accelerated solvent extraction/toluene were found to be the most efficient methods for fly ash PAHs, yielding average recoveries of about 80%. The accelerated solvent extraction/toluene procedure was superior for lignite PAHs, yielding 96% average recovery, whereas ultrasonic and Soxhlet extraction yielded relatively lower recoveries (75% and 67%, respectively).     

Testing the efficiency of extraction of incurred residues from soil with optimized multi-residue method

The reproducibility of extraction of residues from spiked soil samples and from soils containing incurred residues was tested with ¹⁴C-labeled test compounds of different physical-chemical properties. Nearly 100% of the compounds added to the sample before extraction could be recovered with an average reproducibility relative standard deviation (CV) of 5.4%. The additional steps of the determination process (cleanup, evaporation, etc.) contributed to the major part of the variability of the results (CV = 10–20%). The incurred residues were most efficiently extracted with acetone for 30 min followed by the mixture of acetone/ethyl acetate 1:1 for additional 30 min. However, they could only be recovered at various extent (64–90% of total residues), underlying the importance of testing the efficiency of extraction. The residues were identified and quantified by gas chromatography applying thermionic detector. The performance parameters of the method complied with the international method validation guidelines, and they proved to be robust and suitable for determination of pesticide residues in soils of widely different physical–chemical properties.     

Modelling the extraction of soil contaminants with supercritical carbon dioxide

Extractions of volatile organic compounds (VOC’s) in contaminated soil from petroleum site were performed with supercritical carbon dioxide at different temperatures, pressures, extraction times, solvent flow rates, soil moisture contents and soil acidity. Three soil systems were investigated in order to compare the best parameters for extraction. A central composite rotatable design has been used to evaluate the influence of operation conditions on the extraction efficiency to generate model equations representing the types of soil. The results indicate that at least 70-80% of the initial amount of VOC’s can be removed at moderate temperatures even at very high moisture content. Supercritical extraction is best suited to silt type soils which have a low adsorption capacity. VOC’s recoveries from the artificial contaminated soil samples were higher in comparison with real contaminated soils. At moderate temperatures, the extraction efficiency for real soils is low because pollutants bind strongly to the soil.     

Dissipation pathways of organic pollutants during the composting of organic wastes

The organic pollutants (OPs) present in compostable organic residues can be recovered in the final composts leading to environmental impacts related to their use in agriculture. However, the composting process may contribute to their partial dissipation that is classically evaluated through the concentration decrease in extractable OPs, without identification of the responsible mechanisms as mineralization or stabilization of OP as non-extractable residues (NER) or bound residues. The dissipation of four (14)C-labeled OPs (fluoranthene; 4-n-nonylphenol, NP; sodium linear dodecylbenzene sulfonate, LAS; glyphosate) was assessed during composting of sewage sludge and green waste. The dissipation of LAS largely resulted from its mineralization (51% of initial LAS), whereas mineralization was intermediate for NP (29%) and glyphosate (24%), and negligible for fluoranthene. The NER pathway mostly concerned NP and glyphosate, with 45% and 37% of the recovered (14)C being found as NER at the end of composting, respectively. In the final composts, the proportions of water soluble residues of OPs considered as readily available were <11% of recovered (14)C-OPs. However, most fluoranthene remained solvent extractable (72%) and potentially available, whereas only 18% of glyphosate and less than 7% of both NP and LAS remained solvent extractable in the final compost.     

Geochemical fractions of copper in soil chronosequences of selected European floodplains

The influence of soil formation on copper sorption is documented based on chronosequences of soils from three river floodplains in Europe (Danube, Ebro and Elbe). Sequential extraction was used to fractionate copper in original and spiked soils in order to study the long-term and short-term behaviour of copper retention. Copper partitioning among defined geochemical fractions was mainly determined by soil pH and the contents of carbonates, organic matter and Fe-/Mn-oxides and hydroxides. Copper extracted with NH(2)OH.HCl correlated well with the contents of crystalline Fe-oxides and hydroxides, demonstrating increasing retention capacity with progressing soil development. Copper retained in original soils was found in more strongly bound fractions, whereas sorption of freshly added copper was primarily influenced by the presence of carbonates. Beyond the effect of progressing soil formation, variations in organic carbon contents due to different land use history affected the copper retention capacity of the investigated soils.