116 research outputs found

    Modeling aerobic biotransformation of vinyl chloride by vinyl chloride-assimilating bacteria, methanotrophs and ethenotrophs

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    © 2017 Elsevier B.V. Recent studies have investigated the potential of enhanced groundwater Vinyl Chloride (VC) remediation in the presence of methane and ethene through the interactions of VC-assimilating bacteria, methanotrophs and ethenotrophs. In this study, a mathematical model was developed to describe aerobic biotransformation of VC in the presence of methane and ethene for the first time. It examines the metabolism of VC by VC-assimilating bacteria as well as cometabolism of VC by both methanotrophs and ethenotrophs, using methane and ethene respectively, under aerobic conditions. The developed model was successfully calibrated and validated using experimental data from microcosms with different experimental conditions. The model satisfactorily describes VC, methane and ethene dynamics in all microcosms tested. Modeling results describe that methanotrophic cometabolism of ethene promotes ethenotrophic VC cometabolism, which significantly enhances aerobic VC degradation in the presence of methane and ethene. This model is expected to be a useful tool to support effective and efficient processes for groundwater VC remediation

    1,4-dioxane biodegradation in propanotrophs: molecular foundations and implications for environmental remediation

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    1,4-Dioxane (dioxane) has emerged with an escalating concern given its human carcinogenicity and widespread occurrence in groundwater. Bioremediation is promising as an effective and cost-efficient treatment alternative for in situ or ex situ cleanup of dioxane and co-existing pollutants in the field. Soluble di-iron monooxygenases (SDIMOs) are reputed for their essential roles in initiating the cleavage of dioxane and other pollutants. In this doctoral dissertation, molecular foundations for SDIMOs-mediated dioxane biodegradation are untangled to promote the development and implication of site-specific bioremediation and natural attenuation strategies. This dissertation focused on propanotrophic bacteria given their pivotal roles in dioxane metabolism and co-metabolism. The first part of this dissertation is centered on investigating the distinctive catalytic behaviors between two archetypical dioxane degrading enzymes, propane monooxygenase (PRM) and tetrahydrofuran monooxygenase (THM), belonging to group-6 and group-5 SDIMOs, respectively. They are compared from kinetics, inhibition, and substrate range. Results reveal that PRM is more profitable in environmental conditions such as low dioxane concentration, co-existing chlorinated solvents, and many other pollutants suggesting that PRM may has been long underestimated. The second section refines the phylogenies of SDIMOs into six groups. The evaluation sequence of this multi-component enzyme family follows the order: group-4 alkene MO &rightarrow group-5 propane/tetrahydrofuran MO &rightarrow group-6 propane MO &rightarrow group-3 methane/butane MO. Their short-chain gaseous hydrocarbon degradation capabilities evolve from unsaturated to saturated compounds and from low C-H bond to high energy. Results allow a robust bioprospecting of SDIMO. The third part of this dissertation is aimed to untangle downstream dioxane degradation pathways in metabolic degraders via genome the comparison of metabolic and co-metabolic strains. A putative flavin-containing monooxygenase (fmo) gene is cloned and expressed in mc2-155. Unfortunately, no HEAA transformation activity is exhibited by this transformant. Existence of the complete glycolate transformation pathway in all dioxane metabolizers reveals its essential role in dioxane mineralization. As trace levels of dioxane (\u3c1 mg/L) are widely detected in contaminated sites, the fourth part aims to tackle such biotransformation hindrance by bioaugmentation with a novel dioxane co-metabolizer, Azoarcus sp. DD4. DD4 exhibited formidable adaptability and relatively stable performance on dioxane degradation with the supplement of propane, supporting its feasibility for both in situ and ex situ treatment of dioxane even when its concentration is below 100 µg/L. Pure strain study reveals DD4 can overcome the inhibition of cVOCs and degrade them when supplied with propane. Last but not the least, a bioremediation treatment train combining the reductive dehalogenation by halorespiring consortium, SDC-9, and cometabolic oxidation by DD4 to address the commingling contamination of TCE and dioxane. SDC-9 can effectively remove TCE, however, lingering with less-chlorinated but toxic metabolites, vinyl chloride (VC) and cis-dichloroethene (cDCE). Subsequent aerobic bioaugmentation with DD4, can concurrently degrade dioxane, VC, and cDCE

    Toward efficiency in heterogeneous multispecies reactive transport modeling: A particle-tracking solution for first-order network reactions

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    Modeling multispecies reactive transport in natural systems with strong heterogeneities and complex biochemical reactions is a major challenge for assessing groundwater polluted sites with organic and inorganic contaminants. A large variety of these contaminants react according to serial-parallel reaction networks commonly simplified by a combination of first-order kinetic reactions. In this context, a random-walk particle tracking method is presented. This method is capable of efficiently simulating the motion of particles affected by first-order network reactions in three-dimensional systems, which are represented by spatially variable physical and biochemical coefficients described at high resolution. The approach is based on the development of transition probabilities that describe the likelihood that particles belonging to a given species and location at a given time will be transformed into and moved to another species and location afterward. These probabilities are derived from the solution matrix of the spatial moments governing equations. The method is fully coupled with reactions, free of numerical dispersion and overcomes the inherent numerical problems stemming from the incorporation of heterogeneities to reactive transport codes. In doing this, we demonstrate that the motion of particles follows a standard random walk with time-dependent effective retardation and dispersion parameters that depend on the initial and final chemical state of the particle. The behavior of effective parameters develops as a result of differential retardation effects among species. Moreover, explicit analytic solutions of the transition probability matrix and related particle motions are provided for serial reactions. An example of the effect of heterogeneity on the dechlorination of organic solvents in a threedimensional random porous media shows that the power-law behavior typically observed in conservative tracers breakthrough curves can be largely compromised by the effect of biochemical reactions.Postprint (published version

    Determination Of Vinyl-Chloride Utilizing Kinetic Parameters Parameters For A Mycobacterium Strain And An Enrichment Culture

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    A recent study in our lab had suggested that aerobic oxidation of vinyl chloride (VC) was responsible for VC loss at extremely low oxygen concentrations that would be practically classified as anaerobic conditions. However, no aerobic VC-assimilating bacterium had been isolated from the enrichment cultures involved, and therefore no further characterization had been conducted. This study investigated the VC-utilizing kinetics of a Mycobacterium isolate from one of the enrichment cultures (from Cecil Field, FL), and another highly-enriched culture (from Industrial Site 4, CA). By limiting VC and O2 concentrations, thus separately limiting the utilization rates of respective substrates, various kinetic parameters of both cultures were determined. The maximum VC utilization rate (kVC) and half velocity constant for VC (Ks(VC)) of the Mycobacterium isolate were 11.5 nmol/min/mg of protein and 0.16 [MICRO SIGN]M, respectively, while those of the S4 culture were 4.7 nmol/min/mg of protein and 0.51 [MICRO SIGN] M, respectively. The half velocity constants for O2 (Ks(O2)) of the Mycobacterium isolate and S4 culture were 0.06 mg/L and 0.03 mg/L, respectively. There was no measureable O2 threshold identified for either culture. Overall, this study further supported the hypothesis that aerobic VC oxidation could account for loss of VC under commonly defined -anaerobic[DOUBLE VERTICAL LINE] conditions, and provided data for kinetic behavior of related aerobic VC-assimilating bacteria

    Halogenated aliphatic and aromatic aerobic biodegradation via direct metabolism and cometabolism: batch and continuous tests

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    In this thesis the application of biotechnological processes based on microbial metabolic degradation of halogenated compound has been investigated. Several studies showed that most of these pollutants can be biodegraded by single bacterial strains or mixed microbial population via aerobic direct metabolism or cometabolism using as a growth substrates aromatic or aliphatic hydrocarbons. The enhancement of two specific processes has been here object of study in relation with its own respective scenario described as follow: 1st) the bioremediation via aerobic cometabolism of soil contaminated by a high chlorinated compound using a mixed microbial population and the selection and isolation of consortium specific for the compound. 2nd) the implementation of a treatment technology based on direct metabolism of two pure strains at the exact point source of emission, preventing dilution and contamination of large volumes of waste fluids polluted by several halogenated compound minimizing the environmental impact. In order to verify the effect of these two new biotechnological application to remove halogenated compound and purpose them as a more efficient alternative continuous and batch tests have been set up in the experimental part of this thesis. Results obtained from the continuous tests in the second scenario have been supported by microbial analysis via Fluorescence in situ Hybridisation (FISH) and by a mathematical model of the system. The results showed that both process in its own respective scenario offer an effective solutions for the biological treatment of chlorinate compound pollution

    Assessing the joint impact of DNAPL source-zone behavior and degradation products on the probabilistic characterization of human health risk

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    The release of industrial contaminants into the subsurface has led to a rapid degradation of groundwater resources. Contamination caused by Dense Non-Aqueous Phase Liquids (DNAPLs) is particularly severe owing to their limited solubility, slow dissolution and in many cases high toxicity. A greater insight into how the DNAPL source zone behavior and the contaminant release towards the aquifer impact human health risk is crucial for an appropriate risk management. Risk analysis is further complicated by the uncertainty in aquifer properties and contaminant conditions. This study focuses on the impact of the DNAPL release mode on the human health risk propagation along the aquifer under uncertain conditions. Contaminant concentrations released from the source zone are described using a screening approach with a set of parameters representing several scenarios of DNAPL architecture. The uncertainty in the hydraulic properties is systematically accounted for by high-resolution Monte Carlo simulations. We simulate the release and the transport of the chlorinated solvent perchloroethylene and its carcinogenic degradation products in randomly heterogeneous porous media. The human health risk posed by the chemical mixture of these contaminants is characterized by the low-order statistics and the probability density function of common risk metrics. We show that the zone of high risk (hot spot) is independent of the DNAPL mass release mode, and that the risk amplitude is mostly controlled by heterogeneities and by the source zone architecture. The risk is lower and less uncertain when the source zone is formed mostly by ganglia than by pools. We also illustrate how the source zone efficiency (intensity of the water flux crossing the source zone) affects the risk posed by an exposure to the chemical mixture. Results display that high source zone efficiencies are counter-intuitively beneficial, decreasing the risk because of a reduction in the time available for the production of the highly toxic subspecies.Peer ReviewedPostprint (author's final draft
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