Desorption of Nitroaromatic Compounds From Explosive-contaminated Soil by Washing

The soil contaminated by explosive production wastewater was treated by washing using water as solvent. The effect of contact time and temperature, water/soil ratio and washing steps on desorption efficiency was investigated. Six kinetic models—parabolic diffusion model, zero-order equation, pseudo-first-order equation, pseudo-second-order equation, power function equation and Elovich equation—were used to study the desorption kinetics of nitroaromatic compounds from contaminated soil to water. The eluent of contaminated soil before and after washing was characterized by UV–vis analysis. The results showed that the removal rate was fast at the initial stage and then slowed down after 60 min. The desorption of contaminants from soil to water is endothermic. Washing with small quantities of water in high frequency is preferred when water volume is limited. The pseudo-second-order model can be used to describe the desorption process. Soil washing can remove most of the contaminants from the contaminated soil.     

Long-term assessment of natural attenuation: statistical approach on soils with aged PAH contamination

Natural attenuation processes valorization for PAH-contaminated soil remediation has gained increasing interest from site owners. A misunderstanding of this method and a small amount of data available does not encourage its development. However, monitored natural attenuation (MNA) offers a valuable, cheaper and environmentally friendly alternative to more classical options such as physico-chemical treatments (e.g., chemical oxidation, thermal desorption). The present work proposes the results obtained during a long-term natural attenuation assessment of historically contaminated industrial soils under real climatic conditions. This study was performed after a 10 year natural attenuation period on 60 off-ground lysimeters filled with contaminated soils from different former industrial sites (coking industry, manufactured gas plants) whose initial concentration of PAH varied between 380 and 2,077 mg kg^?1. The analysed parameters included leached water characterization, soil PAH concentrations, evaluation of vegetation cover quality and quantity. Results showed a good efficiency of the PAH dissipation and limited transfer of contaminants to the environment. It also highlighted the importance of the fine soil fractions in controlling PAH reactivity. PAH dissipation through water leaching was limited and did not present a significant risk for the environment. This PAH water concentration appeared however as a good indicator of overall dissipation rate, thereby illustrating the importance of pollutant availability in predicting its degradation potential.     

Vapor Pressure Characterization to Predict Contaminant Releases from MGP Site Source Area Soils

Risk-based management of contaminated sites often requires timely screening and identification of source areas that release contaminants to groundwater and other reception of concern. Over-reliance on total concentrations often results in costly site characterization, delays in remediation, and overestimation of the soil volumes targeted for removal or treatment. Advances in diagnostic tools to accelerate source area characterization will improve the reliability of management decisions. The objective of this work was to determine the potential of using vapor pressure measurements as a rapid indicator of the mass release potential of suspected source area soils.

The current work has focused on determining the relationship between partial pressure and mobility for monoaromatic and polycyclic aromatic hydrocarbon (PAH) contaminants in source area soils. This work ascertained that for a wide spectrum of non-ionized, aromatic contaminants in MGP soils, total vapor pressure and benzene partial pressure could be measured with good repeatability. Under controlled conditions, photoionization detector (PID) measurements on 16 soil samples from two MGP sites were found to correlate well to laboratory measurements of equilibrium partitioning and resin-mediated soil contaminant desorption with R² values of over 0.9. Results indicate that vapor pressure correlates well to contaminant mobility in soils.     

Basic examinations on chemical pre-oxidation by ozone for enhancing bioremediation of phenanthrene contaminated soils

Biological treatment of polycyclic aromatic hydrocarbons (PAH) has been demonstrated to be a feasible and common remediation technology which has been successfully applied to the clean-up of contaminated soils. Because bioavailability of the contaminants is of great importance for a successful bioremediation, a chemical pre-oxidation step by ozone was tested to enhance the subsequent biodegradation steps. Oxidation of PAH by ozone should result in reaction products that have a better solubility in water and thus a better bioavailability. A major part of this work was done by examinations of the model substance phenanthrene as a typical compound of PAH. After initial ozonation of phenanthrene, analysis by GC-MS showed at least seven identified conversion-products of phenanthrene. In comparison with phenanthrene these conversion products were more efficiently biodegraded by Sphingomonas yanoikuyae or mixed cultures when the ozonation process resulted in monoaromatic compounds. Primary ozonation products with biphenylic structures were found not to be biodegradable. Investigations into the toxicity of contaminated and ozonated soils were carried out by well-established toxicity assays using Bacillus subtilis and garden cress. The ozonated soils surprisingly showed higher toxic or inhibitory effects towards different organisms than the phenanthrene or PAH itself. The microbial degradation of phenanthrene in slurry reactors by S. yanoikuyae was not enhanced significantly by preozonation of the contaminated soil.     

Microwave-Assisted Process (MAPTM) for the Extraction of Contaminants from Soil

Laboratory-scale tests were performed to evaluate the use of Environment Canada's patented Microwave-Assisted Process (MAP_TM) for the extraction of petroleum hydrocarbons from contaminated soil. The purpose of these tests was to determine the potential for using the process for large-scale processing of contaminated soil. Tests were performed using three soil types: a certified sediment and certified soil, both contaminated with polycyclic aromatic hydrocarbons (PAHs), and spiked peat soil contaminated with long-chain petroleum hydrocarbons. The test methods used were based on existing MAP techniques that have been proven for the sample preparation of contaminated soils for analytical purposes. The parameters evaluated concentrated on those that are amenable to a continuous large-scale process running at atmospheric pressures. This meant using solvents that are inexpensive and readily available in large volumes, low solvent to material ratios, and optimized energy inputs. In general, it was found that microwaves could be used to enhance the solvent extraction of the contaminants from the soil and that the properties of the soil greatly affected the extent to which the contaminants were removed.     

An Investigation of the Ability of a 14C-Labeled Hydrocarbon Mineralization Test to Predict Bioremediation of Soils Contaminated with Petroleum Hydrocarbons

Bioremediation is a widely accepted technology for the remediation of hydrocarbon-contaminated soil. Treatability studies are usually carried out to assess the biodegradation potential of the contaminants and to design optimal treatments. Laboratory studies measuring soil respiration are often used. One method consists of monitoring the mineralization of a ¹⁴C-labeled hydrocarbon surrogate added to the contaminated soil. This study investigates the ability of this method to properly predict the removal of the hydrocarbon contaminants initially found in soils. Mineralization of ¹⁴C-labeled hexadecane was monitored in seven soils contaminated with various hydrocarbon mixtures, both fresh and weathered, in microcosm experiments. Reduction of total petroleum hydrocarbon (TPH) concentrations was measured simultaneously in separate microcosms. Both types of microcosms were subjected to the same amendment regimes. For all soils, poor correlation was observed between the mineralization and TPH reduction data sets. Mineralization data supported contaminants removal data in only one soil. Findings indicate that the radioactive surrogate method does not reliably predict the extent of, and the effect of amendments on, the removal of the hydrocarbons initially present in soil, and may therefore predict suboptimal treatment regimes. Recommendations for soil treatability protocols are provided.     

Does Bioavailability Limit Biodegradation? A Comparison of Hydrocarbon Biodegradation and Desorption Rates in Aged Soils

In order to determine whether bioavailability limits the biodegradability of petroleum hydrocarbons in aged soils, both the biodegradation and abiotic desorption rates of PAHs and n-alkanes were measured at various time points in six different aged soils undergoing slurry bioremediation treatment. Alkane biodegradation rates were always much greater than the respective desorption rates, indicating that these saturated hydrocarbons apparently do not need to be dissolved into the aqueous phase prior to metabolism by soil microorganisms. The biodegradation of PAHs was generally not mass-transfer rate limited during the initial phase, while it often became so at the end of the treatment period when biodegradation rates equaled abiotic desorption rates. However, in all cases where PAH biodegradation was not observed or PAH removal temporarily stalled, bioavailability limitations were not deemed responsible for this recalcitrance since these PAHs desorbed rapidly from the soil into the aqueous phase. Consequently, aged PAHs that are often thought to be recalcitrant due to bioavailability limitations may not be so and therefore may pose a greater risk to environmental receptors than previously thought.     

Biodegrader metabolic expansion during polyaromatic hydrocarbons rhizoremediation

Root-microbe interactions are considered to be the primary process of polyaromatic hydrocarbon (PAH) phytoremediation, since bacterial degradation has been shown to be the dominant pathway for environmental PAH dissipation. However, the precise mechanisms driving PAH rhizostimulation symbiosis remain largely unresolved. In this study, we assessed PAH degrading bacterial abundance in contaminated soils planted with 18 different native Michigan plant species. Phenanthrene metabolism assays suggested that each plant species differentially influenced the relative abundance of PAH biodegraders, though they generally were observed to increase heterotrophic and biodegradative cell numbers relative to unplanted soils. Further study of >1800 phenanthrene degrading isolates indicated that most of the tested plant species stimulated biodegradation of a broader range of PAH compounds relative to the unplanted soil bacterial consortia. These observations suggest that a principal contribution of planted systems for PAH bioremediation may be via expanded metabolic range of the rhizosphere bacterial community.     

Multispecies and monoculture rhizoremediation of polycyclic aromatic hydrocarbons (PAHs) from the soil

In this study, we investigated the potential of multispecies rhizoremediation and monoculture rhizoremediation in decontaminating polycyclic aromatic hydrocarbon (PAH) contaminated soil Plant-mediated PAH dissipation was evaluated using monoplanted soil microcosms and soil microcosms vegetated with several different grass species (Brachiaria serrata and Eleusine corocana). The dissipation of naphthalene and fluorene was higher in the "multispecies" vegetated soil compared to the monoplanted and nonplanted control soil. The concentration of naphthalene was undetectable in the multispecies vegetated treatment compared to 96% removal efficiencies in the monoplanted treatments and 63% in the nonplanted control after 10 wk of incubation. Similar removal efficiencies were obtained for fluorene. However, there was no significant difference in the dissipation of pyrene in both the mono- and multispecies vegetated treatments. There also was no significant difference between the dissipation of PAHs in the monoplanted treatments with different grass species. Principle component analysis (PCA) and cluster analysis were used to evaluate functional diversity of the different treatments during phytoremediation of PAHs. Both PCA and cluster analysis revealed differences in the metabolic fingerprints of the PAH contaminated and noncontaminated soils. However, the differences in metabolic diversity between the multispecies vegetated and monoplanted treatments were not clearly revealed. The results suggest that multispecies rhizoremediation using tolerant plant species rather than monoculture rhizoremediation have the potential to enhance pollutant removal in moderately contaminated soils.     

Degradation of polycyclic aromatic hydrocarbons at low temperature under aerobic and nitrate-reducing conditions in enrichment cultures from northern soils

The potential for biodegradation of polycyclic aromatic hydrocarbons (PAHs)at low temperature and under anaerobic conditions is not well understood, but such biodegradation would be very useful for remediation of polluted sites. Biodegradation of a mixture of 11 different PAHs with two to five aromatic rings, each at a concentration of 10 micro g/ml, was studied in enrichment cultures inoculated with samples of four northern soils. Under aerobic conditions, low temperature severely limited PAH biodegradation. After 90 days, aerobic cultures at 20 degrees C removed 52 to 88% of the PAHs. The most extensive PAH degradation under aerobic conditions at 7 degrees C,53% removal, occurred in a culture from creosote-contaminated soil. Low temperature did not substantially limit PAH biodegradation under nitrate-reducing conditions. Under nitrate-reducing conditions,naphthalene, 2-methylnaphthalene, fluorene, and phenanthrene were degraded. The most extensive PAH degradation under nitrate-reducing conditions at 7 degrees C, 39% removal, occurred in a culture from fuel-contaminated Arctic soil. In separate transfer cultures from the above Arctic soil, incubated anaerobically at 7 degrees C, removal of 2-methylnaphthalene and fluorene was stoichiometrically coupled to nitrate removal. Ribosomal intergenic spacer analysis suggested that enrichment resulted in a few predominant bacterial populations,including members of the genera Acidovorax,Bordetella, Pseudomonas, Sphingomonas, and Variovorax. Predominant populations from different soils often included phylotypes with nearly identical partial 16S rRNA gene sequences (i.e., same genus) but never included phylotypes with identical ribosomal intergenic spacers (i.e., different species or subspecies). The composition of the enriched communities appeared to be more affected by presence of oxygen, than by temperature or source of the inoculum.     

Recovery of mitosporic fungi actively growing in soils after bacterial bioremediation of oily sludge and their potential for removing recalcitrant hydrocarbons

Bacterial bioremediation is a widely used technique to remove or neutralize contaminants. However, the enzymatic capabilities of bacteria are limited and, consequently, recalcitrant compounds remain in the soil. Fungi can help to overcome this drawback, since their enzymatic repertoire is extensive. In this study, the diversity of viable, actively growing, filamentous fungi was explored in soils previously subjected to bioremediation with bacterial consortia from three petroleum exploitation fields. Diversity was estimated using both morphological traits and ITS rDNA sequencing. We recovered a highly diverse group of morphotypes from each field, most of them previously reported genera of fungi associated with bioremediation (Aspergillus, Paecilomyces, and Penicillium), but a high proportion (40%) of the fungal species detected have never previously been reported as being involved in degradation of hydrocarbons. To build evidence of the isolates as potential bioremediation agents, their laccase and peroxidase activities were measured in vitro; peroxidase activity was a common trend in these fungi. The detection of peroxidase activity suggests adaptation of these fungi to the residual contaminants after bacterial action. Bioaugmentation of the fungal isolates in microcosms contaminated with oily sludge resulted in higher removal of the asphaltenic fraction compared to no bioaugmented microcosms. Our method allowed us to screen for and isolate viable mycelia within a contaminated environment, a strategy efficient for our environmental protection goals.     

Various Applications of Soil Contaminant Database Developed for the Central Artery/Tunnel Project

One of the largest environmental assessment programs in the United States was initiated in the early 1990s to determine the chemical characteristics of soil located within the planned alignment for the Central Artery (I-93) / Tunnel (I-90) (CA/T) Project in Boston, Massachusetts. The primary purpose of the program was to support management of the handling and disposal of over 17 million cubic yards of soil to be excavated during construction of the CA/T Project. As part of this work, more than 8,000 soil samples were collected from more than 2,600 soil borings and analyzed for a range of chemical contaminants, including volatile organic compounds, acid/base neutral compounds, total petroleum hydrocarbons, polychlorinated biphenyls, and heavy metals. The soils encountered during the investigations exhibited properties influenced by numerous anthropogenic activities. These activities, such as vehicular emissions, historic industrial/manufacturing operations, and waterfront filling with both building rubble and dredge spoils from Boston Harbor, resulted in soils primarily contaminated with petroleum hydrocarbons and metals. As a result of this program, an extensive database of the chemical constituents present in urban soils in downtown Boston was developed. These results were primarily used to delineate the limits of contaminated areas affecting the planned construction. In addition, the database has been used by the Project to support various soil management activities, as well as by the regulatory community in developing guidelines and criteria governing the management of contaminated soils in Massachusetts. This paper focuses on the various applications of this database throughout the course of the Project, and with the additional aim of stimulating potential future applications by both the regulatory and scientific communities.     

Bioremediation of a petroleum‐contaminated cryic soil: Effects of phosphorus,nitrogen, and temperature

Bioremediation has been shown to be an effective means of treating petroleum‐contaminated soils in cold areas, although the conditions required to maximize bioremediation in cold region (cryic) soils are not well documented. A laboratory study was conducted to investigate the effects of nitrogen and phosphorus levels and temperature on petroleum bioremediation. A cryic entisol contaminated with diesel fuel was treated with nitrogen (0, 400, 800, or 1200 mg/kg of soil) and phosphorus (0, 60, 120, or 180 mg/kg of soil) and incubated at two temperatures (10 and 20°C). At 10°C, bioremediation rates were not affected by fertility treatments. At 20°C, reaction rates were increased by the addition of P, but unaffected by N. Regardless of fertility regime, the rate of diesel loss was much greater in soil incubated at 20°C than in soil incubated at 10°C.     

Degradation of Polycyclic Aromatic Hydrocarbons at Low Temperature under Aerobic and Nitrate-Reducing Conditions in Enrichment Cultures from Northern Soils

The potential for biodegradation of polycyclic aromatic hydrocarbons (PAHs) at low temperature and under anaerobic conditions is not well understood, but such biodegradation would be very useful for remediation of polluted sites. Biodegradation of a mixture of 11 different PAHs with two to five aromatic rings, each at a concentration of 10 μg/ml, was studied in enrichment cultures inoculated with samples of four northern soils. Under aerobic conditions, low temperature severely limited PAH biodegradation. After 90 days, aerobic cultures at 20°C removed 52 to 88% of the PAHs. The most extensive PAH degradation under aerobic conditions at 7°C, 53% removal, occurred in a culture from creosote-contaminated soil. Low temperature did not substantially limit PAH biodegradation under nitrate-reducing conditions. Under nitrate-reducing conditions, naphthalene, 2-methylnaphthalene, fluorene, and phenanthrene were degraded. The most extensive PAH degradation under nitrate-reducing conditions at 7°C, 39% removal, occurred in a culture from fuel-contaminated Arctic soil. In separate transfer cultures from the above Arctic soil, incubated anaerobically at 7°C, removal of 2-methylnaphthalene and fluorene was stoichiometrically coupled to nitrate removal. Ribosomal intergenic spacer analysis suggested that enrichment resulted in a few predominant bacterial populations, including members of the genera Acidovorax, Bordetella, Pseudomonas, Sphingomonas, and Variovorax. Predominant populations from different soils often included phylotypes with nearly identical partial 16S rRNA gene sequences (i.e., same genus) but never included phylotypes with identical ribosomal intergenic spacers (i.e., different species or subspecies). The composition of the enriched communities appeared to be more affected by presence of oxygen, than by temperature or source of the inoculum.     

Influence of Plant Root Exudates on the Mobility of Fuel Volatile Compounds in Contaminated Soils

Vegetation and its associated microorganisms play an important role in the behaviour of soil contaminants. One of the most important elements is root exudation, since it can affect the mobility, and therefore, the bioavailability of soil contaminants. In this study, we evaluated the influence of root exudates on the mobility of fuel derived compounds in contaminated soils. Samples of humic acid, montmorillonite, and an A horizon from an alumi-umbric Cambisol were contaminated with volatile contaminants present in fuel: oxygenates (MTBE and ETBE) and monoaromatic compounds (benzene, toluene, ethylbenzene and xylene). Natural root exudates obtained from Holcus lanatus and Cytisus striatus and ten artificial exudates (components frequently found in natural exudates) were added to the samples, individually and as a mixture, to evaluate their effects on contaminant mobility. Fuel compounds were analyzed by headspace-gas chromatography-mass spectrometry. In general, the addition of natural and artificial exudates increased the mobility of all contaminants in humic acid. In A horizon and montmorillonite, natural or artificial exudates (as a mixture) decreased the contaminant mobility. However, artificial exudates individually had different effects: carboxylic components increased and phenolic components decreased the contaminant mobility. These results established a base for developing and improving phytoremediation processes of fuel-contaminated soils.     

Methodology for using contaminated soil leachability testing to determine soil cleanup levels at contaminated petroleum underground storage tank (UST) sites

The costs of environmental remediation at leaking petroleum underground storage tank (UST) sites are influenced significantly by soil cleanup levels. The use of conservative generic soil cleanup levels may be inappropriate at some sites contaminated by leaking petroleum USTs. At many contaminated sites, a primary objective of site remediation is long‐term protection of water resources (e.g., groundwater) from pollution. Leaching of pollutants from residual soil contamination to groundwater is a primary consideration in establishing site‐specific soil cleanup levels at fuel‐contaminated sites. The use of laboratory soil leachability testing methods may be useful in objectively evaluating the leaching potential of contaminants from residual soil contamination and estimating potential groundwater impacts. Developing soil cleanup levels that are protective of water resources must include a technically sound integration of site‐specific soil leachability data and contaminant attenuation factors. Evaluation of the leaching potentials of soil contaminants may also provide essential supplementary information for other site characterization methods that may be used to evaluate risks to human health. Contaminant leachability testing of soils may provide a cost‐effective and technically based method for determining soil cleanup levels that are protective of groundwater resources at contaminated petroleum UST sites.     

Site-Specific Limitations of Using Urea as a Nitrogen Source in Biodegradation of Petroleum Wastes in Soil

Nutrient addition is important to achieving the carbon/nitrogen balance and successful biodegradation of petroleum contaminants. Urea has been considered as a preferred nitrogen source in enhancing biodegradation, because of its high nitrogen content and commercial availability. This study investigated urea in the biodegradation of petroleum-contaminated soils collected from an arid and sandy area in Egypt. Ammonium nitrate served as the nitrogen amendment control in this study. Biodegradation of petroleum-contaminated soils from Wyoming was monitored as a comparison. Addition of urea failed to improve the enhancement of biodegradation of petroleum-impacted soil from the Egyptian site; in addition, urea demonstrates an adverse effect on the biodegradation rates. Results indicate that urea or its intermediates may inhibit the microorganisms involved in petroleum degradation. Data from this study suggest that the application of urea in the enhancement of biodegradation of petroleum compounds should consider site specificity, and may not be applicable in geological areas or soils structures similar to those in this study.     

Double-tagged fluorescent bacterial bioreporter for the study of polycyclic aromatic hydrocarbon diffusion and bioavailability

Bacterial degradation of polycyclic aromatic hydrocarbons (PAHs), ubiquitous contaminants from oil and coal, is typically limited by poor accessibility of the contaminant to the bacteria. In order to measure PAH availability in complex systems, we designed a number of diffusion-based assays with a double-tagged bacterial reporter strain Burkholderia sartisoli RP037-mChe. The reporter strain is capable of mineralizing phenanthrene (PHE) and induces the expression of enhanced green fluorescent protein (eGFP) as a function of the PAH flux to the cell. At the same time, it produces a second autofluorescent protein (mCherry) in constitutive manner. Quantitative epifluorescence imaging was deployed in order to record reporter signals as a function of PAH availability. The reporter strain expressed eGFP proportionally to dosages of naphthalene or PHE in batch liquid cultures. To detect PAH diffusion from solid materials the reporter cells were embedded in 2 cm-sized agarose gel patches, and fluorescence was recorded over time for both markers as a function of distance to the PAH source. eGFP fluorescence gradients measured on known amounts of naphthalene or PHE served as calibration for quantifying PAH availability from contaminated soils. To detect reporter gene expression at even smaller diffusion distances, we mixed and immobilized cells with contaminated soils in an agarose gel. eGFP fluorescence measurements confirmed gel patch diffusion results that exposure to 2–3 mg lampblack soil gave four times higher expression than to material contaminated with 10 or 1 (mg PHE) g⁻¹.     

In situ assessment of phytotechnologies for multicontaminated soil management

Due to human activities, large volumes of soils are contaminated with organic pollutants such as polycyclic aromatic hydrocarbons, and very often by metallic pollutants as well. Multipolluted soils are therefore a key concern for remediation. This work presents a long-term evaluation of the fate and environmental impact of the organic and metallic contaminants of an industrially polluted soil under natural and plant-assisted conditions. A field trial was followed for four years according to six treatments in four replicates: unplanted, planted with alfalfa with or without mycorrhizal inoculation, planted with Noccaea caerulescens, naturally colonized by indigenous plants, and thermally treated soil planted with alfalfa. Leaching water volumes and composition, PAH concentrations in soil and solutions, soil fauna and microbial diversity, soil and solution toxicity using standardized bioassays, plant biomass, mycorrhizal colonization, were monitored. Results showed that plant cover alone did not affect total contaminant concentrations in soil. However, it was most efficient in improving the contamination impact on the environment and in increasing the biological diversity. Leaching water quality remained an issue because of its high toxicity shown by micro-algae testing. In this matter, prior treatment of the soil by thermal desorption proved to be the only effective treatment.