Petroleum-contaminated Sites Research Articles

Phylogenetic distance and species richness interactively affect the productivity of bacterial communities

Our understanding of how biodiversity influences ecosystem functioning is entering a new stage of its development through the incorporation of information about the evolutionary relatedness of species. Bacteria are prime providers of essential ecosystem services, representing an excellent model system to perform biodiversity-ecosystem function research. By using bacteria isolated from petroleum-contaminated sites, we show that communities composed of poorly related species were more productive than those containing highly related species. The nature of the forces controlling this positive effect of phylogenetic diversity on community productivity depended on the number of species in culture. In communities of two species the positive effect of phylogenetic diversity on productivity was driven by changes in the selection effect. Communities of two distantly related species were dominated by the most productive species in monoculture, whereas communities of two closely related species were dominated by the less productive species in monoculture. In communities of four species the positive effect of phylogenetic diversity on productivity was driven by changes in the complementarity effect. In communities composed of four distantly related species the influence of positive interactions such as facilitation, cross-feeding, and niche partitioning seemed to outweigh the influence of negative interactions such as interference. As a consequence the proportion of species favored by the presence of other species increased as they became less related. Multiple facets of biodiversity may influence ecosystem functioning. Here, we present evidence of an interaction between phylogenetic and taxonomic diversity on community productivity, underlining the importance of considering multiple aspects of biodiversity when studying its impact on ecosystem functioning.

Positive Effects of Bacterial Diversity on Ecosystem Functioning Driven by Complementarity Effects in a Bioremediation Context

Despite their importance as ecosystem drivers, our understanding of the influence of bacterial diversity on ecosystem functioning is limited. After identifying twelve bacterial strains from two petroleum-contaminated sites, we experimentally explored the impact of biodiversity on total density by manipulating the number of strains in culture. Irrespective of the origin of the bacteria relative to the contaminant, biodiversity positively influenced total density. However, bacteria cultured in the crude oil of their origin (autochthonous) reached higher densities than bacteria from another origin (allochthonous) and the relationship between diversity and density was stronger for autochthonous bacteria. By measuring the relative contribution of each strain to total density we showed that the observed positive effect of increasing diversity on total density was mainly due to positive interactions among species and not the presence of a particular species. Our findings can be explained by the complex chemical composition of crude oil and the necessity of a diverse array of organisms with complementary enzymatic capacities to achieve its degradation. The long term exposure to a contaminant may have allowed different bacteria to become adapted to the use of different fractions of the crude, resulting in higher complementarity in resource use in autochthonous bacteria compared to allochthonous ones. Our results could help improve the success of bioaugmentation as a bioremediation technique by suggesting the use of a diversified set of autochthonous organisms.

Geotechnical properties of gas oil-contaminated kaolinite

The leakage of petroleum products contaminates the soil and changes its physical and mechanical properties. This paper is a part of an extensive laboratory program aimed at promoting greater understanding of the influence of petroleum-derived contaminants on the geotechnical properties of soils. The laboratory tests included basic properties, Atterberg limits, consolidation, direct shear, and unconfined compression tests, all of which were carried out on clean and contaminated kaolinite specimens at the same relative compactions. Contaminated specimens were prepared by mixing kaolinite with different gas oil contents. Results indicate an increase in the cohesion and a decrease in both the friction angle and compressibility of kaolinitic soils with increasing the gas oil content. Results are intended to provide an alternative to the treatment methods currently used in practice for petroleum-contaminated sites and help bridge/narrow the gap between research and practice in environmental protection of the sites.

The impact of hazardous waste leachate on performance of clay liners

Penetration of hazardous liquids through waste containment barriers exerts contamination and considerable alterations in geotechnical properties of clay liners. In general, these changes are attributed to the variation of the dielectric constant and the chemistry of the pore fluids which cause changes in soil structure. In the present study, a series of laboratory tests were performed on natural and contaminated clay soil permeated with different hazardous liquids: ethylene glycol and toluene which are generally found in petroleum-contaminated sites, possessing intermediate and low dielectric constants. Toluene was used in its pure form and ethylene glycol was used at various percentages of 0, 20, 40 and 60% by the volume of distilled water. In addition, natural sea water was also utilized as an inorganic fluid for permeation and salinization of the clay soil. The overall test results indicated that plasticity, sedimentation time, unconfined compressive strength, swell and compressibility generally decreased with increasing organic fluid/water concentration, while a slight increase in the permeability values was observed. Pure toluene resulted in diminution of plasticity and considerable flocculation of the particles which caused the soil to become granular. Sea water also caused particle flocculation and reduction in plasticity, swell potential and unconfined compressive strength, although it was noted that compressibility properties remained unchanged compared to distilled water. Finally, the correlation between the electrical resistivity and plasticity index values suggested that the electrical resistivity measurements can be used as a detecting technique for subsurface soil and waste barrier contamination.

Occurrence and distribution of polycyclic aromatic hydrocarbons in organo-mineral particles of alluvial sandy soil profiles at a petroleum-contaminated site

The occurrence and the distribution of 16 USEPA priority pollutants polycyclic aromatic hydrocarbons (PAHs) were investigated in two alluvial sandy soil profiles and in their four sizes of organo-mineral particles (<2μm clay, 2–20μm silt, 20–200μm fine sand, and >200μm coarse sand) beside a typical oil sludge storage site in eastern China. PAHs were mainly enriched in the surface soil (0–20cm) and the concentrations declined in deeper soils, from 3.68 to 0.128μg/g in profile 1 and 10.8 to 0.143μg/g in profile 2 (dry wt.). The PAHs in the upper soil layers of this study site mainly came from combustion pollution, whereas in the lower soil layers petroleum contamination became the major source of PAHs. The content of different sized organo-mineral particles of this alluvial sandy soil decreased in the following order: fine sand>coarse sand>silt>clay. X-ray diffraction (XRD) results showed that all the different sized soil fractions of this study site were dominated by quartz, calcite and feldspar. The particle surface became smoother with size increasing as shown by scanning electron microscope (SEM) images. PAH concentrations varied largely in different sized soil fractions. The highest PAH concentration was associated with clay and decreased in the order: clay>silt>coarse sand>fine sand. Soil organic matter (SOM) content, mineral composition and particle surface characteristics were suggested as three main factors affecting the distribution of PAHs in different sized organo-mineral particles. This study will help to understand the distribution and transport characteristics of PAHs in soil profiles at petroleum-contaminated sites.

A fuzzy-parameterised stochastic modelling system for predicting multiphase subsurface transport under dual uncertainties

A fuzzy-parameterised stochastic modelling system (FPSMS) was proposed in this study to investigate the impacts of uncertainties associated with hydrocarbon contaminant transport in subsurface. FPSMS integrated the multiphase numerical simulator, the fuzzy transformation method, and the Monte Carlo simulation technique into a general modelling framework, and was capable of dealing with coupled probabilistic–possibilistic uncertainties (in fuzzy-parameterised stochastic format). The simulation of light non-aqueous phase spill liquid (LNAPL) in an experimental system was used to demonstrate the applicability of the proposed method. Porosity and intrinsic permeability were considered as stochastic inputs with the means and standard deviations being characterised by fuzzy sets. The study results demonstrated that FPSMS was effective in evaluating the joint impacts of highly uncertain inputs on predictions of the LNAPL movements in subsurface. Compared with traditional fuzzy-stochastic analysis methods, FPSMS was suitable in tackling dual uncertainties, generating outputs with richer information, and even having more efficient calculation algorithms. Also, it could be a good reference for further risk assessment and remediation design for petroleum-contaminated sites.

Biomarkers of petroleum contamination in the digestive gland of Perna viridis (L.)

Oxidative stress responses were evaluated in the digestive gland tissue of Perna viridis exposed to water-accommodated fractions (WAFs) of petrol and diesel at 0.5% and 5% concentrations over 5-, 10-, and 15-day periods. Increased lipid peroxidation, protein carbonyl, DNA integrity, and hydrogen peroxide in WAF-exposed specimens are indicative of oxidative damage due to dissolved petroleum extracts. A consistent increase in superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glutathione-S-transferase, reduced glutathione, and ascorbic acid in WAF-exposed specimens signify the importance of antioxidants in protecting the cell against the oxidative damage arising from petroleum contamination. The responses of field specimens collected from petroleum-contaminated sites support the observed laboratory experimental results. This research recommends the use of these oxidative stress indices in the digestive gland tissue of Perna viridis as biomarkers of petroleum contamination.

Biodegradation of Carbazole and Dibenzothiophene by Bacteria Isolated from Petroleum-Contaminated Sites

ABSTRACT This study reports the isolation of bacterial cultures, capable of selective removal of nitrogen and sulfur from carbazole and dibenzothiophene, respectively. The isolates utilizing carbazole were found to be suitable for biorefining. These were designated as P10 and P11, and were identified as Pseudomonas sp. Growing cells of P10 and P11 could utilize 77% carbazole in 250 and 120 h, respectively. Isolates showing utilization of dibenzothiophene were not suitable for biorefining industry. Results suggest these Pseudomonas isolates may be useful in petroleum biorefining for the selective removal of organically bound nitrogen from petroleum.

Determination of a risk management primer at petroleum-contaminated sites: Developing new human health risk assessment strategy

Total petroleum hydrocarbon (TPH) is an important environmental contaminant that is toxic to human and environmental receptors. However, human health risk assessment for petroleum, oil, and lubricant (POL)-contaminated sites is especially challenging because TPH is not a single compound, but rather a mixture of numerous substances. To address this concern, this study recommends a new human health risk assessment strategy for POL-contaminated sites. The strategy is based on a newly modified TPH fractionation method and includes an improved analytical protocol. The proposed TPH fractionation method is composed of ten fractions (e.g., aliphatic and aromatic EC8–10, EC10–12, EC12–16, EC16–22 and EC22–40). Physicochemical properties and toxicity values of each fraction were newly defined in this study. The stepwise ultrasonication-based analytical process was established to measure TPH fractions. Analytical results were compared with those from the TPH Criteria Working Group (TPHCWG) Direct Method. Better analytical efficiencies in TPH, aliphatic, and aromatic fractions were achieved when contaminated soil samples were analyzed with the new analytical protocol. Finally, a human health risk assessment was performed based on the developed tiered risk assessment framework. Results showed that a detailed quantitative risk assessment should be conducted to determine scientifically and economically appropriate cleanup target levels, although the phase II process is useful for determining the potency of human health risks posed by POL-contamination.

Modeling Biosurfactant-Enhanced Bioremediation Processes for Petroleum-Contaminated Sites

In situ bioremediation is an effective technology for cleaning up petroleum-contaminated sites. To improve efficiencies of conventional bioremediation processes, biosurfactant treatment has received much attention. In this study, an integrated mathematical modeling system was developed for simulating biosurfactant-enhanced bioremediation (BEB) processes. The model includes modules of multiphase, multicomponent flow and transport, biological degradation, and biosurfactant-enhanced remediation. A pilot-scale physical modeling system, with rhamnolipid as biosurfactant, was designed to simulate the BEB process. The results demonstrated that the developed mathematical model is effective in examining the coupled effects of biodegradation and biosurfactant enhancement and can be used for supporting management of petroleum-contaminated sites.

A fuzzy multi-criteria decision analysis approach for the management of petroleum-contaminated sites

This paper presents an effective Fuzzy Multi-Criteria Decision Analysis (FMCDA) approach for contaminated site management. The development was based on: selecting eight criteria for remedial alternative evaluation and determining the weight of criteria importance under uncertainty; addressing various uncertainty issues in remedial alternative assessment process using a fuzzy-set approach based on the questionnaire survey results; evaluating and ranking remedial alternatives by establishing a fuzzy evaluation matrix of remediation alternatives through comprehensively considering different stakeholder opinions and uncertainties within a general decision analysis framework. A case study on the remedial alternative selection for a contaminated site in western Canada is conducted to illustrate the efficiency and applicability of the developed approach.

A Correlation to Estimate the Bioventing Degradation Rate Constant

ABSTRACT Estimating the biodegradation rate is essential when designing a bioremediation strategy for petroleum-contaminated sites, and when evaluating assessment guidelines. However, estimating the biodegradation rate is difficult as the rate constant varies from site to site due to changing site conditions, which include soil type, biological activity, and type of contaminant. Accordingly, bench-scale biodegradation studies were completed using respirometers to measure first-order biodegradation rate constants for gasoline in several soils over 30 days of incubation. A total of seven soils were tested at various gasoline concentrations with constant nutrient ratios and water content. No microbial inhibition was observed for the range of gasoline concentrations studied. Analysis showed that the statistically significant parameters were the initial population of petroleum-degrading microorganisms and the organic matter content. The developed empirical correlation is a simple tool that practioners can use to estimate the biodegradation rate without conducting lengthy and expensive experiments.

Quantification of Aromatic Oxygenase Genes to Evaluate Enhanced Bioremediation by Oxygen Releasing Materials at a Gasoline-Contaminated Site

Subsurface injection of oxygen-releasing materials (ORMs) is frequently performed at petroleum-contaminated sites to stimulate aerobic bioremediation of benzene, toluene, ethylbenzene, and xylenes (BTEX). In this study, qPCR enumeration of aromatic oxygenase genes and PCR-DGGE profiles of bacterial 16S rRNA genes were combined with groundwater monitoring to determine the impact of ORM injection on BTEX bioremediation at a gasoline-contaminated site. Prior to injection, BTEX concentrations were greater than 3 mg/L and DO levels were typically lessthan 2 mg/L, butphenol hydroxylase (PHE) and ring-hydroxylating toluene monooxygenase (RMO) genes were detected in impacted wells indicating the potential for aerobic BTEX biodegradation. Following injection, DO increased, BTEX concentrations decreased substantially, and PHE and RMO genes copies increased by 1-3 orders of magnitude. In addition, naphthalene dioxygenase (NAH) and xylene monooxygenase (TOL) genes were intermittently detected during periods of increased DO. Following depletion of the ORM, DO decreased, BTEX concentrations rebounded, and oxygenase genes were no longer detected. Temporal changes in PCR-DGGE microbial community profiles reflected the dynamic changes in subsurface conditions. Overall, the combination of chemical and geochemical analyses with quantification of aromatic oxygenase genes demonstrated that injection stimulated BTEX biodegradation until the ORM was depleted.

Petroleum-contaminated groundwater remediation systems design: A data envelopment analysis based approach

Groundwater contamination is one of important environmental problems at petroleum-related sites, which is causing more and more attention. It can bring serious adverse effects on the environment and human health. Design of a groundwater remediation system is desired for supporting the management of petroleum-contaminated sites. Due to high remediation cost and extensive alternatives, efficient remediation design needs to be determined. Data envelopment analysis (DEA) is an approach to measure the relative efficiencies of decision-making units (DMUs) with multiple inputs and multiple outputs without underlying assumptions. However, few of these studies were applied to the design of groundwater remediation systems, where efficient alternatives for remediation systems design need to be determined. This paper proposes a hybrid decision support approach based on data envelopment analysis to determine the most preferable design alternatives for groundwater remediation systems. The total remediation system cost, amount of additional wells, and manpower requirements will be employed as the input variables, while the removal efficiency and technical feasibility as the output variables. The proposed approach will be applied to a case study of designing a groundwater remediation system at a petroleum-contaminated site in western Canada. The most preferable design alternative can be obtained to provide effective decision support for cleaning up the contaminated site.

Enumeration of aromatic oxygenase genes to evaluate biodegradation during multi-phase extraction at a gasoline-contaminated site

Multi-phase extraction (MPE) is commonly used at petroleum-contaminated sites to volatilize and recover hydrocarbons from the vadose and saturated zones in contaminant source areas. Although primarily a physical treatment technology, the induced subsurface air flow can potentially increase oxygen supply and promote aerobic biodegradation of benzene, toluene, ethylbenzene, and xylenes (BTEX), the contaminants of concern at gasoline-contaminated sites. In this study, real-time PCR enumeration of aromatic oxygenase genes and PCR-DGGE profiles were used to elucidate the impact of MPE operation on the aquifer microbial community structure and function at a gasoline-contaminated site. Prior to system activation, ring-hydroxylating toluene monooxygenase (RMO) and naphthalene dioxygenase (NAH) gene copies were on the order of 10 6 to 10 10 copies L −1 in groundwater samples obtained from BTEX-impacted wells. Aromatic oxygenase genes were not detected in groundwater samples obtained during continuous MPE indicating decreased populations of BTEX-utilizing bacteria. During periods of pulsed MPE, total aromatic oxygenase gene copies were not significantly different than prior to system activation, however, shifts in aromatic catabolic genotypes were noted. The consistent detection of RMO, NAH, and phenol hydroxylase (PHE), which catabolizes further oxidation of hydroxylated BTEX metabolites indicated the potential for aerobic biodegradation of dissolved BTEX during pulsed MPE.

Optimization of Remediation Operations at Petroleum-Contaminated Sites through a Simulation-based Stochastic-MCDA Approach

A simulation-based stochastic-multi-criteria decision analysis (MCDA) approach was developed for optimizing groundwater remediation operations through integrating the contaminant transport modeling, dual-phase vacuum extraction (DPVE) process modeling, deterministic MCDA, and Monte Carlo simulation into a general framework. A petroleum-contaminated site in western Canada was selected as the study case for demonstrating the applicability of the proposed method. Totally, 12 scenarios were designed for site remediation. Nine criteria were used for evaluating each alternative through the developed MCDA methods. The economical factors consisted of operational cost associated with DPVE and groundwater remediation. Environmental performances were determined based on the magnitude of risky and highly risky areas of benzene, toluene, ethyl-benzene, and xylene (BTEX contamination that were predicted through developed models. The study results demonstrated that the proposed stochastic MCDA method provides more complete information of possible rankings of alternatives than conventional methods. The decision makers cannot only obtain the ranking information under uncertainty directly, but also gain an in-depth understanding on the relative derivation and closeness among different alternatives.

Assessing spatial distribution and joint uncertainty of TPH-fractions: Indicator kriging and sequential indicator simulation

Petroleum hydrocarbon (PHC) contamination is one of the most common contaminants in soils and remediation of PHC-contaminated sites requires methods for characterizing the spatial distribution of PHC on a site. Few studies have compared the performance of indicator kriging (IK) and sequential indicator simulation (SIS) in site characterization of petroleum-contaminated sites, or the application of these methods given the fraction based guidelines. The objectives of this study were to determine if IK and SIS indicate similar contaminated areas and to examine how the probability of exceeding thresholds changes when multiple fractions are considered simultaneously. An abandoned refinery near Kamsack, Saskatchewan, characterized by clay-textured soils was sampled and analyzed for PHC fractions (F2 and F3). The probability of a location exceeding a fraction’s remediation criteria was determined using IK and SIS. Based on critical probability thresholds, IK indicated a greater area was contaminated by F2 (6.3%) and F3 (0.8%) than SIS (4.5 and 0.6%, respectively). When the remediation criteria for both F2 and F3 were considered simultaneously, “dependent” and “independent” cases were examined. The dependent case assumed perfect correlation and used the maximum probability of either F2 or F3 as the new estimate. The independent case assumed no correlation and evaluated the probability of F2 &gt; 2500 mg kg–1 or F3 &gt; 6600 mg kg–1. The dependent case resulted in a smaller contaminated area than the independent case in both IK and SIS. On this site the differences between the two methods were small, although IK did smooth the distribution. Key words: Sequential indicator simulation, indicator kriging, geostatics, petroleum hydrocarbon contamination, uncertainty

A Stepwise-Inference-Based Optimization System for Supporting Remediation of Petroleum-Contaminated Sites

Groundwater contamination by leakage and spill of petroleum hydrocarbons from underground storage tanks has been a major environmental concern. Among various remediation alternatives, the vacuum-enhanced free product recovery (VFPR) is an important technology to extract light nonaqueous-phase liquids (LNAPLs) from subsurface. However, efficient design of a VFPR system was challenging to practitioners, since the process of hydrocarbon removal is costly and time consuming. To address such a problem, an integrated study system for optimizing the VFPR process was developed through coupling a numerical modeling system, a multivariate regression technique and nonlinear optimization model into a general framework. A two-dimensional multiphase flow simulation system was provided for modeling VFPR processes. An iterative stepwise-inference regression (ISIR) method was advanced for establishing a linkage between remediation actions and system responses. A nonlinear optimization model embedded with ISIR was then established for generating desired operating conditions. The results from a case study demonstrated that the established optimization model could effectively analyze tradeoffs between various environmental and economical considerations, and provide effective decision supports for site remediation practices. Compared with the conventional stepwise-cluster analysis method, the proposed ISIR method was more efficient and reliable in approximating relationships between remediation actions and system responses, and could significantly enhance the robustness of optimization solutions.

Remediation of Petroleum-contaminated Sites through Simulation of a DPVE-aided Cleanup Process: Part 1. Model Development

The remediation system is complicated with dual-phase vacuum extraction (DPVE), residual phase cleanup, and groundwater treatment. Studies for individual system components cannot effectively reflect interactions among various processes of contaminant fate and transport. Thus, an integrated consideration that incorporates transport, DPVE-aided remediation within a general framework is desired. As an extension of previous studies, a hybrid modeling system for simulating DPVE-aided remediation and contaminant transport is proposed for forecasting of both remediation process and contaminant mitigation at a petroleum-hydrocarbon contaminated site. A three-dimension multiphase and multicomponent subsurface model is combined with a numerical simulation of DPVE remediation process. The developed simulation system is applied to a petroleum-contaminated site in western Canada wherein DPVE remediation process has been in progress. The developed system is effective in simulating effects of free-product recovery and groundwater cleanup through processes of DVPE and groundwater remediation.

Remediation of Petroleum-contaminated Sites through Simulation of a DPVE-aided Cleanup Process: Part 2. Remediation Design

Remediation of petroleum-contaminated sites is usually a challenging task. It is hard to identify and customize a desired remediation technique or technique-combination into specific on-site conditions due mainly to the difficulties in gaining insight into the complex source and medium conditions in aquifer systems. Moreover, it is exigent to remediate sites where low-permeability soil layers exist. This study presents an integrated approach based on the simulation of a DPVE-aided (dual-phase vacuum extraction aided) remediation process for the identification and customization of desired remediation techniques, as well as its application to a site located in western Canada. Data of the specific site conditions, the forecasted results of contaminant transport, and the scenarios of remediation techniques with different treatment efficiencies are examined. Then the proposed approach was applied to design six remediation alternatives based on combinations of several technologies and the provision of analyses for system designs and costs. The study will help provide decision support for further remediation actions to be taken at the site.