Download or read book Kinetic and Modeling Investigations of the Anaerobic Reductive Dechlorination of Chlorinated Ethylenes Using Single and Binary Mixed Cultures and Silicon based Organic Compounds as Slow release Substrates written by Seungho Yu and published by . This book was released on 2003 with total page 394 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Modeling Kinetics and Inhibition of Chloroethene Reductive Dechlorination in Mixed Culture written by Qi Meng and published by . This book was released on 2014 with total page 161 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chlorinated ethenes such as tetrachloroethene (PCE) and trichloloethene (TCE) are among the most prevalent contaminants in soil, sediments and groundwaters. Currently, Insitu bioremediation via anaerobic reductive dechlorination has become a widely used technology for groundwater contaminated with chlorinated ethenes. To better understand the reductive dechlorination remediation process and the inter-relationships among the complex microbial communities that comprise it, a comprehensive biokinetic model was recently developed at Cornell University by Gretchen Heavner, a modification of an earlier Cornell model developed by Donna Fennell. The Heavner model uses specific biomasses based on quantitative PCR-based population data, and under some conditions can accurately predict kinetics of dechlorination, fermentation of electron donors, and competition for electron donors between dechlorinators and methanogens, and generation of methane. However, the platform used to run the model - STELLA® (High Performance Systems) - is cumbersome for simulation of long time-spans, limiting the model's utility. Furthermore, the model uses an empirical, "mRNA-tuning" technique to improve data fits at high PCE-loadings, which makes the model descriptive, rather than predictive, in such cases. Additionally, electron donor fermentation is not predicted well at high electron-donor feeding rates. The overall purpose of this thesis research was to address some of the limitations of the Heavner model. The STELLA® model was successfully converted to run in MATLAB® using Runge-Kutta 4th-order integration. The model fits at high-PCE and high electron-donor loadings were improved by utilizing the inhibitory effects of high PCE on dechlorination and methanogenesis, and by postulating additional pathways of butyrate's fermentation and acetate's hydrogenation to storage products. Model simulations indicate that by adding 2nd-order Haldane inhibition instead of mRNA tuning, the model revised in this thesis research predicts the dechlorination, methanogenesis and donor fermentation well over a broad range of PCE feeding rates. Moreover, when simulating donor fermentation at high-PCE-loadings, butyrate's fermentations and acetate's hydrogenation to storage products must be considered to obtain a mass balance between butyrate consumption and product formation.

Download or read book Anaerobic Reductive Dechlorination of TCE and TCFE in TCE Contaminated Sediments written by Jae-Hyuk Lee and published by . This book was released on 2006 with total page 280 pages. Available in PDF, EPUB and Kindle. Book excerpt: This research focused on the enhanced reductive dechlorination of trichloroethene (TCE) and its surrogate, trichlorofluoroethene (TCFE), using two bioremediation methods in anaerobic conditions. Two anaerobic bioremediation studies were conducted to investigate the effects of microbial communities in the presence of different electron acceptors and donors during anaerobic reductive dechlorination of TCE and TCFE. The first study was conducted in the groundwater microcosm bottles, filled with groundwater and sediments collected from Richmond site, CA. Parallel reductive dechlorination of TCE and TCFE was evaluated in the presence of fumarate and its product, succinate, while active reduction of high background concentrations of sulfate (2.5 mM) occurred. Because sulfate was assumed as a favorable electron acceptor during reductive dechlorination of chlorinated aliphatic hydrocarbons (CAHs), all microcosms receiving TCE and TCFE with substrates showed enhanced reductive dechlorination activity and even no substrate addition microcosms generated biotransformation products. From the electron mass balance calculations, more than 87.5% of electrons went to sulfate reduction and less than 10% of available electrons involved in dechlorination after sulfate reductions. After amending varying concentrations of sulfate (0 2.5 mM), no inhibition was found between reductive dechlorination of TCE and sulfate reduction. The result indicated that reductive dechlorination could be directly competed with sulfate reduction for available electrons. The second study investigated the effectiveness of in situ push-pull tests to evaluate bioaugmentation in physical aquifer models (PAMs) using dehalogenating strains to reductively dechlorinate TCE to ethene and TCFE to FE in the TCE contaminated sediments. Complete reduction of TCE to ethene occurred in less than 14 days with repeated additions of TCE (13.0 to 46.0 mg/L) and TCFE (15.0 mg/L) was completely transformed to FE in under 24 days. Increased rate and extent of dechlorination in the bioaugmented PAM compared to the nonaugmented control PAM indicated successful transport of the bioaugmented culture through the PAM. Similar transformation rates and time course of TCE and TCFE also indicated that TCFE was a bioprobe for reductive dechlorination of TCE. TCE and TCFE were transformed to cisdichloroethene (c-DCE) and cis-dichlorofluoroethene (c-DCFE) respectively at two of the three sampling ports after 50 days of incubation in the nonaugmented PAM indicating reductive dechlorination activity of indigenous microorganisms. The results showed that it is possible to increase the rate and extent of reductive dechlorination of TCE and TCFE by bioaugmentation and that push-pull tests are effective tools for detecting and quantifying these processes in situ. The third study focused on numerical modeling of the second study. The objectives of this study were (1) to evaluate a simplified method for estimating retardation factors for injected solutes and bioaugmented microorganisms using "pushpull" test injection phase breakthrough curves, (2) to identify whether bioaugmented microorganisms have kept the same transformation capacity of Evanite culture using Michaelis-Menten kinetics by the values provided by Yu et al. (2005) and to verify in situ rates of TCFE reductive dechlorination rates of push-pull tests by numerical modeling, and (3) to investigate a reasonable answer for the nonuniform recovery of ethene and FE during the activity test and the push-pull test. The bioaugmented microorganisms were effectively transported through Hanford sediment. The estimated retardation factor was 1.33. A numerical simulation predicted cell transport in the PAM as far as port 5. This was qualitatively confirmed by cell counts obtained during bioaugmentation but, cells were distributed nonuniformly. The transport test indicated that TCE and TCFE transport was relatively retarded compared to coinjected bromide tracer (retardation factors ranged from 1.33-1.62 for TCE and from 1.44-1.70 for TCFE). The modeling simulation of Michaelis-Menten kinetics for the activity test was well matched for reductive dechlorination rates for TCE and less dechlorinated ethenes using the previous published values of kmax and Ks of chlorinated ethenes by Yu et al. (2005); the model match indicated that the bioaugmented microorganisms kept the same transformation capacity as the original source, Evanite culture (Yu et al., 2005) over 4 months in the PAM. A numerical simulation resulted in the simple first order FE production rate of 1 day' using STOMP code (2002) and the value of FE production rate was in the range of the transformation rates of TCFE during the activity test. The bioaugmented PAM has caused slow loss of injected CAHs during the activity test and the push-pull test.

Download or read book Kinetics of Reductive Dechlorination of Trichloroethane TCA by Anaerobic Biofilms written by Rittmann Bruce E. and published by . This book was released on 1995 with total page 78 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Compendium of Technical Papers on the Reductive Dechlorination of Chlorinated Solvents written by J. Gossett and published by . This book was released on 1997 with total page 50 pages. Available in PDF, EPUB and Kindle. Book excerpt: This compendium of technical papers represents three years of work in the investigation of the anaerobic biodegradation of tetrachloroethylene (PCE). Cornell researchers had previously developed a methanol (MeOH)/PCE enrichment culture which dechlorinates high concentrations of PCE and other chlorinated ethenes to ethene (ETH), representing complete detoxification. This culture dechlorinates PCE at unprecedented, high rates with efficient use of MeOH as the electron donor for reductive dechlorination. However, research at Cornell showed that MeOH was not the direct donor for PCE dechlorination, but rather H2. MeOH and other reductants found to support dechlorination merely serve as H2 precursors. Three alternative electron donors (ethanol, butyrate, and lactate) were evaluated to circumvent the problem of methanogenic competition for the supplied donor. The final selected substrate was used in a continuous-flow reactor study with the H2/PCE enrichment culture. Engineering studies examined the kinetics of, chlorinated ETH utilization, with emphasis on vinyl chloride (VC) dechlorination to ETH. Acclimation and induction issues were explored. Microbiological studies towards a better understanding of the nature and the requirements of the dechlorinating organisms were explored. The nutrition of the dechlorinating organisms was examined with the goal of finding and identifying reliable high-potency sources if the nutrients.

Download or read book Reductive Dechlorination of Chlorinated Ethenes by Mixed Anaerobic Consortia written by Bhaskar Ballapragada and published by . This book was released on 1996 with total page 654 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Effect of Different Inhibitors on Dechlorination Methanogenesis and Acetogenesis in an Anaerobic Pce fed Culture written by Anna P. Carney and published by . This book was released on 1995 with total page 294 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Numerical Simulation of Anaerobic Reductive Dechlorination of CAHs in Continuous Flow Systems written by Nizar Ahmad Mustafa and published by . This book was released on 2012 with total page 362 pages. Available in PDF, EPUB and Kindle. Book excerpt: Halogenated organic compounds have had widespread and massive applications in industry, agriculture, and private households, for example, as degreasing solvents, flame retardants and in polymer production. They are released to the environment through both anthropogenic and natural sources. The most common chlorinated solvents present as contaminants include tetrachloroethene (PCE, perchloroethene) and trichloroethene (TCE). These chlorinated solvents are problematic because of their health hazards and persistence in the environment, threatening human and environmental health. Microbial reductive dechlorination is emerging as a promising approach for the remediation of chlorinated solvents in aquifers. In microbial reductive dechlorination, specialized bacteria obtain energy for growth from metabolic dechlorination reactions that convert PCE to TCE, cis-1,2-dichloroethene (cDCE), vinyl chloride (VC), and finally to benign ethene. Field studies show incomplete dechlorination of PCE to ethene due to lack of electron donors or other populations competing for the electron donor. Mathematical models are good tools to integrate the processes affecting the fate and transport of chlorinated solvents in the subsurface. This thesis explores the use of modeling to provide a better understanding of the reductive dehalogenation process of chlorinated solvents and their competition with other microorganisms for available electron donors in continuous flow systems such as a continuous stirred tank reactor (CSTR) and a continuous flow column. The model is a coupled thermodynamic and kinetic model that includes inhibition kinetics for the dechlorination reactions, thermodynamic constraints on organic acids fermentation and has incorporated hydrogen competition among microorganisms such as homoacetogenesis, sulfate reducers and ferric iron reducers. The set of equations are coupled to those required for modeling a CSTR. The system of model equations was solved numerically using COMSOL 3.5 a, which employs finite-element methods. The kinetic model was verified by simulation results compared to previously published models and by electron balances. The simulation process progressed by simulating the anaerobic reductive dechlorination, coupled with thermodynamic limitation of electron donor fermentation in batch systems to the modeling of CSTR, and finally to simulate anaerobic reductive dechlorination in continuous flow column, aquifer column including the processes of advection, dispersion and sorption along with the microbial processes of dehalogenation, fermentation, iron and sulfate reduction. The simulations using the developed model captured the general trends of the chemical species, and a good job predicting the dynamics of microbial population responses either the CSTRs or continuous flow column. Although, the kinetic of anaerobic dechlorination processes of chlorinated solvents in those systems have been researched in the past, little progress has been made towards understanding the combined effects of the dechlorination and thermodynamic constraints in continuous flow systems. This work provides a rigorous mathematical model for describing the coupled effects of these processes.

Download or read book Synergistic Reductive Dechlorination of 1 1 1 trichloroethane and Trichloroethene and Aerobic Degradation of 1 4 dioxane written by Yihao Luo and published by . This book was released on 2018 with total page 64 pages. Available in PDF, EPUB and Kindle. Book excerpt: Widespread use of chlorinated solvents for commercial and industrial purposes makes co-occurring contamination by 1,1,1-trichloroethane (TCA), trichloroethene (TCE), and 1,4-dioxane (1,4-D) a serious problem for groundwater. TCE and TCA often are treated by reductive dechlorination, while 1,4-D resists reductive treatment. Aerobic bacteria are able to oxidize 1,4-D, but the biological oxidation of 1,4-D could be inhibited by TCA, TCE, and their reductive transformation products. To overcome the challenges from co-occurring contamination, I propose a two-stage synergistic system. First, anaerobic reduction of the chlorinated hydrocarbons takes place in a H2-based hollow-fiber "X-film" (biofilm or catalyst-coated film) reactor (MXfR), where "X-film" can be a "bio-film0" (MBfR) or an abiotic "palladium-film" (MPfR). Then, aerobic removal of 1,4-D and other organic compounds takes place in an O2-based MBfR. For the reductive part, I tested reductive bio-dechlorination of TCA and TCE simultaneously in an MBfR. I found that the community of anaerobic bacteria can rapidly reduce TCE to cis-dichloroethene (cis-DCE), but further reductions of cis-DCE to vinyl chloride (VC) and VC to ethene were inhibited by TCA. Also, it took months to grow a strong biofilm that could reduce TCA and TCE. Another problem with reductive dechlorination in the MBfR is that mono-chloroethane (MCA) was not reduced to ethane. In contrast, a film of palladium nano-particles (PdNPs), i.e., an MPfR, could the simultaneous reductions of TCA and TCE to mainly ethane, with only small amounts of intermediates: 1,1-dichloroethane (DCA) (~3% of total influent TCA and TCE) and MCA (~1%) in continuous operation. For aerobic oxidation, I enriched an ethanotrophic culture that could oxidize 1,4-D with ethane as the primary electron donor. An O2-based MBfR, inoculated with the enriched ethanotrophic culture, achieved over 99% 1,4-D removal with ethane as the primary electron donor in continuous operation. Finally, I evaluated two-stage treatment with a H2-based MPfR followed by an O2-MBfR. The two-stage system gave complete removal of TCA, TCE, and 1,4-D in continuous operation.

Download or read book Reductive Dechlorination Sustained by Microbial Chain Elongation written by Aide Robles and published by . This book was released on 2019 with total page 29 pages. Available in PDF, EPUB and Kindle. Book excerpt: Trichloroethene (TCE) is a ubiquitous soil and groundwater contaminant. The most common bioremediation approach for TCE relies on the process of reductive dechlorination by Dehalococcoides mccartyi. D. mccartyi uses TCE, dichloroethene, and vinyl chloride as electron acceptors and hydrogen as an electron donor. At contaminated sites, reductive dechlorination is typically promoted by adding a fermentable substrate, which is broken down to short chain fatty acids, simple alcohols, and hydrogen. This study explored microbial chain elongation (MCE), instead of fermentation, to promote TCE reductive dechlorination. In MCE, microbes use simple substrates (e.g., acetate, ethanol) to build medium chain fatty acids and also produce hydrogen during this process. Soil microcosm using TCE and acetate and ethanol as MCE substrates were established under anaerobic conditions. In soil microcosms with synthetic groundwater and natural groundwater, ethene was the main product from TCE reductive dechlorination and butyrate and hydrogen were the main products from MCE. Transfer microcosms using TCE and either acetate and ethanol, ethanol, or acetate were also established. The transfers with TCE and ethanol showed the faster rates of reductive dechlorination and produced more elongated products (i.e., hexanoate). The microbial groups enriched in the soil microcosms likely responsible for chain elongation were most similar to Clostridium genus. These investigations showed the potential for synergistic microbial chain elongation and reductive dechlorination of chlorinated ethenes.

Download or read book A Model for the Prediction of Biologically Mediated Reductive Dechlorination Pathways written by Cynthia L. Cozza and published by . This book was released on 1990 with total page 198 pages. Available in PDF, EPUB and Kindle. Book excerpt: The environment has been exposed to a number of hazardous chlorinated organic compounds. These compounds may be anaerobically biotransformed by sequential reductive dechlorination reactions in which the chlorine atoms are replaced with hydrogen atoms. Because reductive dechlorination processes may occur very slowly in the environment and chlorine position affects the fate and toxicity of the compound in the environment, it is desirable to develop a model to predict the products of these reactions. This project was designed to examine the reductive dechlorination pathways of various chlorinated aromatic compounds in relation to additional substituents on the ring and to develop an empirical model to predict these pathways. The model is based on the structural properties of the compound. Molecular structures and properties such as net atomic charges were calculated using the published semiempirical MNDO (Modified Neglect of Differential Overlap) method, Versions 4.01 and 5.01 at the Cornell National Supercomputer Facility. Net carbon-chlorine bond charges are compared for chlorinated positions on the ring or aliphatic chain. These data provide a means for correlating charge with the position of dechlorination. The pathways predicted from this model agreed well with experimentally determined pathways for several classes of chlorinated organic compounds including: phenols, dihydroxybenzenes, benzoic acids, and anilines.

Download or read book The Biological Reductive Dechlorination of Chlorinated Compounds in a High rate Anaerobic Reactor written by and published by . This book was released on 1999 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Mechanisms Chemistry and Kinetics of Anaerobic Biodegradation of Cis Dichloroethene and Vinyl Chloride written by and published by . This book was released on 2000 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: Anaerobic biological processes can result in PCE and TCE destruction through conversion to cis-dichloroethene (cDCE) then to vinyl chloride (VC), and finally to ethene. Here, the chlorinated aliphatic hydrocarbons (CAHs) serve as electron acceptors in energy metabolism, requiring electron donors such as hydrogen from an external source. The purpose of this study was to learn more about the biochemistry of cDCE and VC conversion to ethene, to better understand the requirements for electron donors, and to determine factors affecting the rates of CAH degradation and organism growth. The biochemistry of reductive dehalogenation of VC was studied with an anaerobic mixed culture enriched on VC. In other studies on electron donor needs for dehalogenation of cDCE and VC, competition for hydrogen was found to occur between the dehalogenators and other microorganisms such as methanogens and homoacetogens in a benzoate-acclimated dehalogenating methanogenic mixed culture. Factors affecting the relative rates of destruction of the solvents and their intermediate products were evaluated. Studies using a mixed PCE-dehalogenating culture as well as the VC enrichment for biochemical studies suggested that the same species was involved in both cDCE and VC dechlorination, and that cDCE and VC competitively inhibited each other's dechlorination rate.

Download or read book Investigation of Community Dynamics and Dechlorination Processes in Chlorinated Ethane degrading Microbial Cultures written by Ariel Grostern and published by . This book was released on 2009 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: The purpose of this research was to investigate the microorganisms, genetics and biochemistry of anaerobic dechlorination of chlorinated ethanes, which are common groundwater contaminants. Specifically, this project used mixed microbial cultures to study the dechlorination of 1,2-dichloroethane (1,2-DCA), 1,1,2-trichloroethane (1,1,2-TCA) and 1,1,1-trichloroethane (1,1,1-TCA).A mixed microbial culture enriched from a contaminated multilayered aquifer in West Louisiana dechlorinated 1,2-DCA, 1,1,2-TCA, tetrachloroethene, trichloroethene, cis-dichloroethene and vinyl chloride (VC) to non-toxic ethene when amended with ethanol as the electron donor. 16S rRNA gene sequence analysis revealed the presence of the putative dechlorinating organisms Dehalobacter and Dehalococcoides spp. Denaturing gradient gel electrophoresis analysis and quantitative PCR (qPCR) with species-specific primers demonstrated that both organisms grew during the dichloroelimination of 1,2-DCA to ethene. Conversely, during the dichloroelimination of 1,1,2-TCA to VC only Dehalobacter grew, while during the reductive dechlorination of VC to ethene only Dehalococcoides grew. Further enrichment with 1,2-DCA, H2 and acetate yielded a co-culture of Dehalobacter and Acetobacterium spp. that did not dechlorinate other chlorinated ethanes or ethenes. Dehalobacter grew in the presence but not in the absence of 1,2-DCA, while Acetobacterium growth was not affected by 1,2-DCA. A novel putative Dehalobacter -associated 1,2-DCA reductive dehalogenase gene was identified and was shown to be transcribed only in the presence of 1,2-DCA.An enrichment microbial culture derived from a 1,1,1-TCA-contaminated site in the northeastern United States was also studied. This culture, referred to as MS, reductively dechlorinated 1,1,1-TCA to 1,1-dichloroethane (1,1-DCA) and then to monochloroethane (CA) when amended with methanol, ethanol, acetate and lactate. 16S rRNA gene sequence analysis revealed the presence of the putative dechlorinating organism Dehalobacter sp., whose growth during 1,1,1-TCA and 1,1-DCA dechlorination was confirmed by qPCR. In the presence of chlorinated ethenes, dechlorination 1,1,1-TCA by the culture MS was slowed, while dechlorination of 1,1-DCA was completely inhibited. Experiments with cell-free extracts and whole cell suspensions of culture MS suggested that chlorinated ethenes have direct inhibitory effects on 1,1,1-TCA reductive dehalogenase(s), while the inhibition of 1,1-DCA dechlorination may be due to effects on non-dehalogenase components of Dehalobacter sp. cells. Additionally, two novel reductive dehalogenase genes associated with 1,1,1-TCA reductive dechlorination were identified.

Download or read book Natural Attenuation of Chlorinated Ethenes by Anaerobic Reductive Dechlorination Coupled with Aerobic Cometabolism written by DEREK. VEERKAMP and published by . This book was released on 1999-03-01 with total page 119 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chlorinated solvents and their daughter products are the most common contaminants of groundwater at industrial and military facilities in the United States. Limitations of conventional technologies have intensified efforts to find alternative methods to remediate contaminated sites to regulatory goals set by CERCLA. Natural attenuation of chlorinated solvents is a promising alternative to traditional pump and treat methods but has not been well understood or widely accepted. This modeling study investigated the ability of TCE to completely degrade under various aquifer conditions and rate order constants. It also examined a case study of a former landfill site at Moody AFB. We found unusually high flow of ground water by advection or dispersion inhibits the complete degradation of TCE. High concentrations of sulfate or nitrate inhibit the creation of methanogenic conditions and therefore inhibit reductive dechlorination of TCE. We also found an electron donor co-contaminant a critical factor for the complete destruction of TCE because it creates anaerobic conditions. The model illustrated a possible explanation for the lack of down gradient contaminants at the landfill site may be the coupling of reductive dechlorination and cometabolism naturally attenuation the contaminants.

Download or read book The Biological Reductive Dechlorination of Chlorinated Compounds in a High rate Anaerobic Reactor written by and published by . This book was released on 1999 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Natural Attenuation of Chlorinated Ethenes by Anaerobic Reductive Dechlorination Coupled with Aerobic Cometabolism written by Derek D. Veerkamp (1LT, USAF.) and published by . This book was released on 1999 with total page 210 pages. Available in PDF, EPUB and Kindle. Book excerpt: