Using Nanoscale Zero-Valent Iron for the Remediation of Polycyclic Aromatic Hydrocarbons Contaminated Soil

Abstract

The sites contaminated with recalcitrant organic compounds, such as polycyclic aromatic hydrocarbons (PAHs) with multiple benzene rings, are colossal and ubiquitous environmental problems. They are relatively nonbiodegradable and mutagenic, and 16 of them are listed in the U.S. Environment Protection Agency priority pollutants. Thus, the efficient and emerging remediation technologies for removal of PAHs in contaminated sites have to be uncovered urgently. In this decade, the zero-valent iron (ZVI) particles have been used successfully in the laboratory, pilot, and field, such as degradation of chlorinated hydrocarbons and remediation of the other pollutants. Nevertheless, as far as we know, little research has investigated for soil remediation; this study used nanoscale ZVI particles to remove pyrene in the soil. The experimental variables were determined, including reaction time, iron particle size, and dosage. From the results, both the micro- and nanoscales of ZVI were capable of removing the target compound in soil, but the higher removal efficiencies were by nanoscale ZVI because of the massive specific surface area. The optimal operating conditions to attain the best removal efficiency of pyrene were obtained while adding nanoscale ZVI 0.1 g/g soil within 60 min and 150 rpm of mixing. Thus, nanoscale ZVI has proved to be a promising remedy for PAH-contaminated soil in this study, as well as an optimistically predictable application for additional pilot and field studies.     

Remediation of soil contaminated with pyrene using ground nanoscale zero-valent iron

The sites contaminated with recalcitrant polycyclic aromatic hydrocarbons (PAHs) are serious environmental problems ubiquitously. Some PAHs have proven to be carcinogenic and hazardous. Therefore, the innovative PAH in situ remediation technologies have to be developed instantaneously. Recently, the nanoscale zero-valent iron (ZVI) particles have been successfully applied for dechlorination of organic pollutants in water, yet little research has investigated for the soil remediation so far. The objective in this work was to take advantage of nanoscale ZVI particles to remove PAHs in soil. The experimental factors such as reaction time, particle diameter and iron dosage and surface area were considered and optimized. From the results, both microscale and nanoscale ZVI were capable to remove the target compound. The higher removal efficiencies of nanoscale ZVI particles were obtained because the specific surface areas were about several dozens larger than that of commercially microscale ZVI particles. The optimal parameters were observed as 0.2 g iron/2 mL water in 60 min and 150 rpm by nanoscale ZVI. Additionally, the results proved that nanoscale ZVI particles are a promising technology for soil remediation and are encouraged in the near future environmental applications. Additionally, the empirical equation developed for pyrene removal efficiency provided the good explanation of reaction behavior. Ultimately, the calculated values by this equation were in a good agreement with the experimental data.     

Remediation of Soil Contaminated with Pyrene Using Ground Nanoscale Zero-Valent Iron

Abstract

The sites contaminated with recalcitrant polycyclic aromatic hydrocarbons (PAHs) are serious environmental problems ubiquitously. Some PAHs have proven to be carcinogenic and hazardous. Therefore, the innovative PAH in situ remediation technologies have to be developed instantaneously. Recently, the nanoscale zero-va-lent iron (ZVI) particles have been successfully applied for dechlorination of organic pollutants in water, yet little research has investigated for the soil remediation so far. The objective in this work was to take advantage of nanoscale ZVI particles to remove PAHs in soil. The experimental factors such as reaction time, particle diameter and iron dosage and surface area were considered and optimized. From the results, both microscale and nanoscale ZVI were capable to remove the target compound. The higher removal efficiencies of nanoscale ZVI particles were obtained because the specific surface areas were about several dozens larger than that of commercially microscale ZVI particles. The optimal parameters were observed as 0.2 g iron/2 mL water in 60 min and 150 rpm by nanoscale ZVI. Additionally, the results proved that nanoscale ZVI particles are a promising technology for soil remediation and are encouraged in the near future environmental applications. Additionally, the empirical equation developed for pyrene removal efficiency provided the good explanation of reaction behavior. Ultimately, the calculated values by this equation were in a good agreement with the experimental data.     

Bioremediation of soil contaminated with polynuclear aromatic hydrocarbons (PAHs): a review

Polynuclear aromatic hydrocarbons (PAHs) constitute a group of priority pollutants which are present at high concentrations in the soils of many industrially contaminated sites. Criteria established for the removal or treatment or both of soils contaminated with PAHs vary widely within and between nations. The bioremediation of contaminated soils with in-situ, on-site, and bioreactor techniques is reviewed, together with the factors affecting PAH degradation. Current in-situ remediation techniques are considered ineffective for the removal of most PAHs from contaminated soil. On-site 'landforming' methods have been used successfully (and within a reasonable period of time) to degrade only those PAHs with three or fewer aromatic rings. Bioreactors have proved most effective for soil remediation, since conditions for enhanced degradation can be achieved most readily. However, bioreactors are still at the development stage, and further research is required to optimise their efficiency and economy for routine use. Degradation of the more recalcitrant high-molecular-weight PAHs is contaminated soil has not been particularly successful to date. Further research needs are identified to help develop bioremediation into a most cost-effective technology. The importance of full site assessments and treatability studies for successful application in the field is emphasised.     

Removal of sorbed polycyclic aromatic hydrocarbons from soil, sludge and sediment samples using the Fenton's reagent process

The use of the Fenton's reagent process has been investigated for the remediation of environmental matrices contaminated by polycyclic aromatic hydrocarbons (PAHs). Laboratory experiments were first conducted in aqueous solutions, to study the kinetics of oxidation and adsorption of PAHs. Benzo[a]pyrene was more rapidly degraded than adsorbed, while only partial oxidation of fluoranthene occurred. In the case of benzo[b]fluoranthene, its adsorption prevented its oxidation. Besides competition effects between PAHs were found, with slower oxidation of mixtures as compared to single PAH solutions. Apparition of some by-products was observed, and a di-hydroxylated derivative of benzo[a]pyrene could be identified under our conditions. Consequently, application to solid environmental matrices (soil, sludge and sediment samples) was performed using large amounts of reagents. The efficiency of the Fenton treatment was dependent on the matrix characteristics (such as its organic carbon content) and the PAH availability (correlated to the date and level of contamination). However, no pH adjustment was required, as well as no iron addition due to the presence of iron oxides in the solid matrices, suggesting the potential application of Fenton-like treatment for the remediation of PAH-contaminated environmental solids.     

Dissolution and removal of PAHs from a contaminated soil using sunflower oil

This study reports on the feasibility of remediation of polycyclic aromatic hydrocarbon (PAH) contaminated soils using sunflower oil, an environmentally-friendly solvent. Batch experiments were performed to test the influence of oil/soil ratio on the remediation of PAH contaminated soil, and to test the mass transfer behaviors of PAHs from soil to oil. An empirical model was employed to describe the kinetics of PAH dissolution and to predict equilibrium concentrations of PAHs in oil. PAH containing oil was regenerated using active carbon. Results show that dissolution of PAHs from a Manufactured Gas Plant (MGP) soil at oil/soil ratios of one or two were almost the same. Nearly all PAHs (81-100%) could be removed by sunflower oil dissolution. Mass transfer coefficients for low molecular PAHs namely fluoranthene, phenanthrene and anthracene were one or two orders of magnitude higher than those for high molecular PAHs with 4-6 rings. Ninety milliliters of PAH containing oil could be regenerated by 10 g active carbon in a batch reactor. Such a remediation procedure indicates that sunflower oil is a promising agent for the removal of PAHs from MGP soils. However, further research is required before the method can be used for in situ remediation of contaminated sites.     

Roles of oxidant,activator, and surfactant on enhanced electrokinetic remediation of PAHs historically contaminated soil

Electrokinetic (EK) remediation technology can enhance the migration of reagents to soil and is especially suitable for in situ remediation of low permeability contaminated soil. Due to the long aging time and strong hydrophobicity of polycyclic aromatic hydrocarbons (PAHs) from historically polluted soil, some enhanced reagents (oxidant, activator, and surfactant) were used to increase the mobility of PAHs, and remove and degrade PAHs in soil. However, under the electrical field, there are few reports on the roles and combined effect of oxidant, activator, and surfactant for remediation of PAHs historically contaminated soil. In the present study, sodium persulfate (PS, oxidant, 100 g L^?1) or/and Tween 80 (TW80, surfactant, 50 g L^?1) were added to the anolyte, and citric acid chelated iron(II) (CA-Fe(II), activator, 0.10 mol L^?1) was added to catholyte to explore the roles and contribution of enhanced reagents and combined effect on PAHs removal in soil. A constant voltage of 20 V was applied and the total experiment duration was 10 days. The results showed that the removal rate of PAHs in each treatment was PS + CA-Fe(II) (21.3%) > PS + TW80 + CA-Fe(II) (19.9%) > PS (17.4%) > PS + TW80 (11.4%) > TW80 (8.1%) > CK (7.5%). The combination of PS and CA-Fe(II) had the highest removal efficiency of PAHs, and CA-Fe(II) in the catholyte could be transported toward anode via electromigration. The addition of TW80 reduced the electroosmotic flow and inhibited the transport of PS from anolyte to the soil, which decreased the removal of PAHs (from 17.4 to 11.4% with PS, from 21.3 to 19.9% with PS+CA-Fe(II)). The calculation of contribution rates showed that PS was the strongest enhancer (3.3~9.9%), followed by CA-Fe(II) (3.9~8.5%) (with PS), and the contribution of TW80 was small and even negative (?1.4~0.6%). The above results indicated that the combined application of oxidant and activator was conducive to the removal of PAHs, while the addition of surfactant reduced the EOF and the migration of oxidant and further reduced the PAHs removal efficiency. The present study will help to further understand the role of enhanced reagents (especially surfactant) during enhanced EK remediation of PAHs historically contaminated soil.

     

Remediation of DDTs contaminated soil in a novel Fenton-like system with zero-valent iron

Application of a novel Fenton-like system with zero-valent iron, EDTA and Air (ZVI/EDTA/Air) was investigated to degrade dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyldichloroethane, and dichlorodiphenyldichloroethylene (DDE) in the actual contaminated soil from an organochlorine pesticide site. It was found DDTs in the soil were effectively degraded by the system at room temperature, ambient atmosphere pressure and near neutral pH. The dosages of EDTA and ZVI were the dominant factors influencing the removal of contaminants. An increase of EDTA from 0.05 to 0.2 mM and ZVI from 1 to 5 g L^?1 improved the removal of the contaminants significantly. However, excessive amount of EDTA led to a negative effect on the degradation process. Meanwhile, EDTA was simultaneously degraded so as to avoid the secondary pollution risk on soil remediation. Only a small amount of 4,4′-DDE and 2,2-bis(4-chlorophenyl)-1-chloroethylene (4,4′-DDMU) generated as the intermediates of DDT degradation during the process. Our investigation suggests that the Fenton-like system is a promising alternative for remediation of organochlorine pesticides contaminated soils.     

Chemical and bioanalytical characterisation of PAHs in risk assessment of remediated PAH-contaminated soils

Polycyclic aromatic hydrocarbons (PAHs) are common contaminants in soil at former industrial areas; and in Sweden, some of the most contaminated sites are being remediated. Generic guideline values for soil use after so-called successful remediation actions of PAH-contaminated soil are based on the 16 EPA priority pollutants, which only constitute a small part of the complex cocktail of toxicants in many contaminated soils. The aim of the study was to elucidate if the actual toxicological risks of soil samples from successful remediation projects could be reflected by chemical determination of these PAHs. We compared chemical analysis (GC-MS) and bioassay analysis (H4IIE-luc) of a number of remediated PAH-contaminated soils. The H4IIE-luc bioassay is an aryl hydrocarbon (Ah) receptor-based assay that detects compounds that activate the Ah receptor, one important mechanism for PAH toxicity. Comparison of the results showed that the bioassay-determined toxicity in the remediated soil samples could only be explained to a minor extent by the concentrations of the 16 priority PAHs. The current risk assessment method for PAH-contaminated soil in use in Sweden along with other countries, based on chemical analysis of selected PAHs, is missing toxicologically relevant PAHs and other similar substances. It is therefore reasonable to include bioassays in risk assessment and in the classification of remediated PAH-contaminated soils. This could minimise environmental and human health risks and enable greater safety in subsequent reuse of remediated soils.     

Remediation of PAH contaminated soils: application of a solid-liquid two-phase partitioning bioreactor

The feasibility of a two-step treatment process has been assessed at laboratory scale for the remediation of soil contaminated with a model mixture of polycyclic aromatic hydrocarbons (PAHs) (phenanthrene, pyrene, and fluoranthene). The initial step of the process involved contacting contaminated soil with thermoplastic, polymeric pellets (polyurethane). The ability of three different mobilizing agents (water, surfactant (Biosolve) and isopropyl alcohol) to enhance recovery of PAHs from soil was investigated and the results were compared to the recovery of PAHs from dry soil. The presence of isopropyl alcohol had the greatest impact on PAH recovery with approximately 80% of the original mass of PAHs in the soil being absorbed by the polymer pellets in 48 h. The second stage of the suggested treatment involved regeneration of the PAH loaded polymers via PAH biodegradation, which was carried out in a solid-liquid two-phase partitioning bioreactor. In addition to the PAH containing polymer pellets, the bioreactor contained a microbial consortium that was pre-selected for its ability to degrade the model PAHs and after a 14 d period approximately 78%, 62% and 36% of phenanthrene, pyrene, and fluoranthene, respectively, had been desorbed from the polymer and degraded. The rate of phenanthrene degradation was shown to be limited by mass transfer of phenanthrene from the polymer pellets. In case of pyrene and fluoranthene a combination of mass transfer and biodegradation rate might have been limiting.     

零价铁与厌氧微生物协同还原地下水中的硝基苯

通过间歇式实验,考察了零价铁与厌氧微生物协同还原地下水中硝基苯的效果。实验结果表明,由零价铁腐蚀为厌氧微生物提供H2电子供体还原硝基苯的效果明显优于零价铁和微生物单独作用,硝基苯去除率分别提高21.8%和57.0%。弱酸性条件有利于协同反应进行,当初始pH为5.0和6.0时,4 d后硝基苯去除率比初始pH为7.0时的提高74.4%和35.2%。增加零价铁投加量可提高协同还原的效果,零价铁最佳投加量为250 mg/L。零价铁腐蚀产生的Fe2+无法作为电子供体被微生物利用,但可作为无机营养元素促进协同过程。由于零价铁产H2速率受表面覆盖物影响不明显,在地下水修复过程中可保证协同效果并延长零价铁的使用寿命。     

Distribution of polycyclic aromatic hydrocarbons in thirty typical soil profiles in the Yangtze River Delta region, east China

Polycyclic aromatic hydrocarbons (PAHs) were quantified in 30 soil profiles from the Yangtze River Delta Region, in east China. Relative concentrations of PAH compounds with different benzene rings and ratios of fluoranthene to fluoranthene plus pyrene and benz(a)anthracene to benz(a)anthracene plus chrysene were used to identify the possible sources of soil PAHs. Total concentrations of 15 PAHs in topsoils ranged from 8.6 to 3881 microg kg(-1) with an average of 397 microg kg(-1). Half of the soil samples were considered to be contaminated with PAHs (>200 microg kg(-1)) and two sampling sites were heavily polluted by PAHs with concentrations >1000 microg kg(-1). Phenanthrene was found in soils below a depth of 100 cm in half of the sampling sites, but the detectable ratio of benzo(a)pyrene decreased sharply from 100% in topsoil to 0 in the 4th horizon.     

Removal of polycyclic aromatic hydrocarbons from soil: a comparison between bioremoval and supercritical fluids extraction

Polycyclic aromatic hydrocarbons (PAHs) are carcinogenic substances which are resistant to environmental degradation due to their highly hydrophobic nature. Soils contaminated with PAHs pose potential risks to human and ecological health, therefore concern over their adverse effects have resulted in extensive studies on their removal from contaminated soils. The main purpose of this study was to compare experimental results of PAHs removal, from a natural certified soil polluted with PAHs, by biological methods (using bioaugmentation and biostimulation in a solid-state culture) with those from supercritical fluid extraction (SFE), using supercritical ethane as solvent. The comparison of results between the two methods showed that maximal removal of naphthalene, acenaphthene, fluorene, and chrysene was performed using bioremediation; however, for the rest of the PAHs considered (fluoranthene, pyrene, and benz(a)anthracene) SFE resulted more efficient. Although bioremediation achieved higher removal ratios for certain hydrocarbons and takes advantage of the increased rate of natural biological processes, it takes longer time (i.e. 36 d vs. half an hour) than SFE and it is best for 2-3 PAHs rings.     

Modelling of geochemical and isotopic changes in a column experiment for degradation of TCE by zero-valent iron

Zero-valent iron (ZVI) permeable-reactive barriers have become an increasingly used remediation option for the in situ removal of various organic and inorganic chemicals from contaminated groundwater. In the present study a process-based numerical model for the transport and reactions of chlorinated hydrocarbon in the presence of ZVI has been developed and applied to analyse a comprehensive data set from laboratory-scale flow-through experiments. The model formulation includes a reaction network for the individual sequential and/or parallel transformation of chlorinated hydrocarbons by ZVI, for the resulting geochemical changes such as mineral precipitation, and for the carbon isotope fractionation that occurs during each of the transformation reactions of the organic compounds. The isotopic fractionation was modelled by formulating separate reaction networks for lighter ((12)C) and heavier ((13)C) isotopes. The simulation of a column experiment involving the parallel degradation of TCE by hydrogenolysis and beta-elimination can conclusively reproduce the observed concentration profiles of all collected organic and inorganic data as well as the observed carbon isotope ratios of TCE and its daughter products.     

Prediction of complete bioremediation periods for PAH soil pollutants in different physical states by mechanistic models

Mass-transfer models and biodegradation models were developed for three theoretical physical states of polycyclic aromatic hydrocarbons (PAHs) in soil. These mechanistic models were used to calculate the treatment periods necessary for complete removal of the PAH pollutants from the soil under batch conditions. Results indicate that the bioremediation of PAHs in such systems is mainly mass-transfer limited. The potential for bioremediation as a treatment technique for PAH contaminated soils is therefore mainly determined by the mass-transfer dynamics of PAHs. Under mass-transfer limited conditions simplified mathematical models, based on the assumption of a zero dissolved PAH concentrations, can be used to predict the period of time needed for complete bioremediation.     

Polycyclic aromatic hydrocarbons in fuel-oil contaminated soils, Antarctica

Where fuel oil spills have occurred on Antarctic soils polycyclic aromatic hydrocarbons (PAH) may accumulate. Surface and subsurface soil samples were collected from fuel spill sites up to 30 years old, and from nearby control sites, and analysed for the 16 PAHs on the USEPA priority pollutants list, as well as for two methyl substituted naphthalenes, 1-methylnaphthalene and 2-methylnaphthalene. PAH levels ranged from 41-8105 ng g-1 of dried soil in the samples from contaminated sites and were below detection limits in control site samples. PAH were detected in surface soils and had migrated to lower depths in the contaminated soil. The predominant PAH detected were naphthalene and its methyl derivatives.     

Treatment of PAHs in contaminated soil by extraction with aqueous DNA followed by biodegradation with a pure culture of Sphingomonas sp

The biodegradation of polycyclic aromatic hydrocarbons (PAHs) in aqueous deoxyribonucleic acid (DNA) solution from contaminated soil washing was investigated. Initial data with a model effluent consisting of anthracene, phenanthrene, pyrene and benzo[a]pyrene that were individually dissolved in 1% aqueous DNA solution confirmed their positive degradation by Sphingomonas sp. at around 10(8)CFU mL(-1) initial cell loading. For anthracene and phenanthrene, complete removal was achieved within 1h treatment. Degradation of pyrene and benzo[a]pyrene took a relatively longer time of a few days and weeks, respectively. DNA-dissolved PAHs were also degraded relatively faster than PAH crystals in aqueous medium to suggest that the binding of the PAHs in the polymer does not pose serious constraint to bacterial uptake. The DNA was stable against the PAH-degrading bacteria. Parallel experiments with actual DNA solutions obtained during pyrene extraction from an artificially spiked soil also showed similar results. Close to 100% pyrene degradation was achieved after 1d treatment. With its chemical stability, the cell-treated DNA was re-used up to four cycles without a considerable decline in extraction performance.     

Efficacy of in-situ for the remediation of PAH contaminated soils

Polycyclic aromatic hydrocarbons (PAHs) are of environmental concern because many PAHs are either carcinogens or potential carcinogens. Petroleum products are a major source of PAHs. The occurrence of PAH contamination is widespread and novel treatment technologies for the remediation of contaminated soils are necessary.Ozone has been found to be extremely useful for the degradation of PAHs in soils. For these compounds, the reaction with molecular ozone appears to be the more important degradation pathway. Greater than 95% removal of phenanthrene was achieved with an ozonation time of 2.3 h at an ozone flux of 250 mg h⁻¹. After 4.0 h of treatment at an ozone flux of 600 mg h⁻¹, 91 % of the pyrene was removed. We have also found that the more hydrophobic PAHs (e.g. chrysene) react more slowly than would be expected on the basis of their reactivity with ozone, suggesting that partitioning of the contaminant into soil organic matter may reduce the reactivity of the compound. Even so, after 4 h of exposure to ozone, the chrysene concentration in a contaminated Metea soil was reduced from 100 to 50 mg kg⁻¹ .Ozone has been found to be readily transported through columns packed with a number of geological materials, including Ottawa sand, Metea soil, Borden aquifer material and Wurtsmith aquifer material. All of these geological materials exerted a limited (finite) ozone demand, i.e. the rate of ozone degradation in soil columns is very slow after the ozone demand is met. Moisture content was found to increase the ozone demand, most likely owing to the dissolution of gaseous ozone into the pore water. As once the initial ozone demand is met, little degradation of ozone is observed, it should be possible to achieve ozone penetration to a considerable distance away from the injection well, suggesting that in-situ ozonation is a feasible means of treating uncontaminated unsaturated soils. This is substantiated by two field studies where in-situ ozonation was apparently successful at remediating the sites.     

Polycyclic aromatic hydrocarbons in crude oil-contaminated soil: A two-step method for the isolation and characterization of PAHs

A two-step analytical method is developed for the isolation and characterization of polycyclic aromatic hydrocarbons (PAHs) in crude oil contaminated soil. In the first step, those crude oil components were isolated which are easily mobilized with water from the contaminated soil (determination of groundwater pollution potential). In the second step, the fraction containing the remaining crude oil compounds was extracted using toluene. After the cleanup of the fractions, both fractions were analyzed using high-performance liquid chromatography (HPLC). The HPLC of the toluene extracted fraction shows that along with the sixteen priority pollutants from the US-EPA list, many other polycyclic aromatic hydrocarbons (PAHs) are present as well. It is evident from the chromatograms that a significant amount of PAHs are present as is also the case in the fractions eluted by water. The described method allows the determination of total organic pollutants from crude oil, some of them being potential groundwater contaminants. The major part of the total pollutants could not be mobilized by water and therefore remains in the soil, which was extracted in the second step.     

The effect of ryegrass (Lolium perenne) on decrease of PAH content in long term contaminated soil

The biodegradation of polycyclic aromatic hydrocarbons in microecosystems containing long-term contaminated soil was investigated. Soil was contaminated by different chemicals, including PAHs since World War II. Aging of the soil was expected to act as a principal factor limiting biodegradation. Half of the microecosystems contained ryegrass (Lolium perenne) and long-term selected natural soil microflora originally present in contaminated soil. The others contained contaminated soil with natural microflora only. Half of the microecosystems in each parallel experiment was fertilised with N-P-K fertiliser. Cultivation was carried out at 12 and 18 months in a greenhouse with a natural photoperiod and the ability to degrade 15 chosen PAH was investigated. For analysis, the soil from each pot was divided into three horizontal layers for mutual comparison among layers and each layer was further divided into four equal samples. Soil extracts were analysed using HPLC. After a one-year-cultivation period the content of the monitored PAHs declined to 50%. Mostly, there were no significant differences between the microecosystems. Best degraded were fluoranthene and pyrene, which were the major contaminants present in original soil. Also, other compounds were successfully degraded, even benzo[a]pyrene and benzo[ghi]perylene. Dibenz[a,h]anthracene and indeno[1,2,3-cd]pyrene were the only PAHs, examined that showed no significant degradation. Although some differences between the soil layers were detected, no conclusive trends could be found. However, significantly lower concentrations of PAHs were determined mostly in the bottom layer of the analysed profiles. In vegetated microecosystems the decline of PAHs concentrations was more remarkable after 18 months cultivation.