Download or read book A Comparison of Modeling Approaches in Simulating Chlorinated Ethene Removal in a Constructed Wetland by a Microbial Consortia written by Jason S. Campbell and published by . This book was released on 2002-03 with total page 113 pages. Available in PDF, EPUB and Kindle. Book excerpt: The purpose of this study is to compare different approaches to modeling the reductive dechlorination of chlorinated ethenes in the anaerobic region of an upward flow constructed wetland by microbial consortia. A controlled simulation experiment that compares three different approaches to modeling the degradation of chlorinated ethenes in wetland environments is conducted and investigates how each of the modeling approaches affect simulation results. Concepts like microbial growth in the form of a biofilm and spatially varying contaminant concentrations bring the validity of the CSTR assumption into question. These concepts are incorporated into the different modeling approaches to evaluate the CSTR assumption. Model simulations show that spatially varying contaminant concentrations have a significant effect on contaminant effluent concentrations. Additionally, the significance of the incorporation of a biofilm concept depends on the time characteristics of both diffusive mass transport and reaction kinetics.
Download or read book Modeling Chlorinated Ethene Removal in Constructed Wetlands written by Colby D. Hoefar and published by . This book was released on 2000-03 with total page 114 pages. Available in PDF, EPUB and Kindle. Book excerpt: The purpose of this study is to gain understanding of the dynamics of the processes that degrade Perchloroethene (PCE) to ethylene, or carbon dioxide (Co2), within the confines of a constructed wetland. A system dynamics approach will be used. This model is focused on identifying and optimizing the naturally occurring processes in stratified wetland sediment that reduce mass, toxicity, mobility, volume or concentration of contaminants in groundwater. Contaminant fate and transport within a wetland system is extremely complex and the mechanisms that drive wetland behavior are dynamic. Confidence in the model was built through verification and testing. Reasonable behavior resulted from a reasonable range of parameter values. The structure of the model represents the mechanisms and their interactions of an actual wetland system. This study provides a fundamental understanding of contaminant fate and transport in a constructed wetland and gives some insight for implementation. Testing identified specific parameters of typical wetland plant species, which could be optimized to have the most effect on contaminant fate. These parameters were the radius of aerobic influence and the number of roots per square meter. A remediation manager can use this model to explore system behavior by controlling or optimizing specific parameters to better manage contaminant fate and transport in a constructed wetland, saving time and resources.
Download or read book Modeling Chlorinated Ethene Removal in the Methanogenic Zone of Constructed Wetlands written by Randall L. Roberts and published by . This book was released on 2001-03 with total page 185 pages. Available in PDF, EPUB and Kindle. Book excerpt: The purpose of this study is to gain understanding of the dynamics of the processes that degrade Perchloroethene (PCE) to ethene, within the confines of the methanogenic zone of a constructed wetland. A system dynamics modeling approach is used. This model is focused on determining conditions that will enhance contaminant degradation. The chemical and biological processes within the methanogenic zone of a wetland system are extremely complex and dynamic processes. The model is broken up into three simultaneous processes: dechlorination, methanogenesis, and fermentation. The system behavior of the methanogenic zone can be adequately described by the classical formulations of representative microbial reactions acting simultaneously within each process in response to substrate limitation. The zone is assumed to be homogeneous and well mixed. This study provides a fundamental understanding of the complex interactions within the methanogenic zone of a constructed wetland and gives some insight for implementation. Testing identified flow rate, hydrogen concentration, and initial PCE biomass as specific parameters, which could be optimized to have the most effect on contaminant fate.
Download or read book Modeling Chlorinated Ethene Removal in the Methanogenic Zone of Constructed Wetlands A System Dynamics Approach written by and published by . This book was released on 2001 with total page 185 pages. Available in PDF, EPUB and Kindle. Book excerpt: The purpose of this study is to gain understanding of the dynamics of the processes that degrade Perchloroethene (PCE) to ethene, within the confines of the methanogenic zone of a constructed wetland. A system dynamics modeling approach is used. This model is focused on determining conditions that will enhance contaminant degradation. The chemical and biological processes within the methanogenic zone of a wetland system are extremely complex and dynamic processes. The model is broken up into three simultaneous processes: dechlorination, methanogenesis, and fermentation. The system behavior of the methanogenic zone can be adequately described by the classical formulations of representative microbial reactions acting simultaneously within each process in response to substrate limitation. The zone is assumed to be homogeneous and well mixed. This study provides a fundamental understanding of the complex interactions within the methanogenic zone of a constructed wetland and gives some insight for implementation. Testing identified flow rate, hydrogen concentration, and initial PCE biomass as specific parameters, which could be optimized to have the most effect on contaminant fate.
Download or read book Modelling Chlorinated Ethene Removal in the Methanogenic Zone of Constructed Wetlands written by Randall L. Roberts and published by . This book was released on 2001 with total page 370 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Modeling Optimization and Sensitivity Analysis of Reductive Dechlorination of Chlorinated Ethenes with Microbial Competition in Groundwater written by Matthew Barrie Willis and published by Ann Arbor, Mich. : University Microfilms International. This book was released on 2000 with total page 390 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book An Anion Characterization of a Constructed Wetland Used for Chlorinated Ethene Remediation written by Bradley M. Bugg and published by . This book was released on 2001-03 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chlorinated ethene's physical properties as well as its ubiquitous state at DOD installations makes it a priority for innovative remediation efforts. Current techniques are expensive and time consuming to maintain. Constructed wetlands suggest an inexpensive and operational alternative to conventional technologies. Sub-surface flow wetlands provide the anaerobic zones necessary to reduce the recalcitrant chlorinated solvents prior to anaerobic or aerobic mineralization of its daughter products. A vertical flow cell to include sequential sedimentary layers of two hydric soil lifts and a mix of hydric soil and woody compost was the subject of this investigation. This study focused on the statistical significance among the three constructed strata. Concentrations of mono-carboxylic acids and other anions are indicators of the reductive conditions necessary for remediation. Acid anion concentrations were expected to be higher in the assumed anaerobic strata of the constructed cell as a result of the fermentation of humic substances. Decreases in sulfate and nitrate were also expected over the upward flowing, wetland profile due to the reductive, anoxic conditions. Evidence in this study validate these assumptions and suggest that constructed wetlands are a viable alternative to current remediation methods. Findings also suggest manipulation of the physical parameters such as strata depth, soil type, flow rate, etc of a wetland could increase the cell's remediation effectiveness.
Download or read book Bioaugmentation for Groundwater Remediation written by Hans F. Stroo and published by Springer Science & Business Media. This book was released on 2012-10-02 with total page 421 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume provides a review of the past 10 to 15 years of intensive research, development and demonstrations that have been on the forefront of developing bioaugmentation into a viable remedial technology. This volume provides both a primer on the basic microbial processes involved in bioaugmentation, as well as a thorough summary of the methodology for implementing the technology. This reference volume will serve as a valuable resource for environmental remediation professionals who seek to understand, evaluate, and implement bioaugmentation.
Download or read book Determination of Chlorinated Solvent Contamination in an Upward Flow Constructed Wetland written by Bryan C. Opperman and published by . This book was released on 2002-03-01 with total page 133 pages. Available in PDF, EPUB and Kindle. Book excerpt: The purpose of this study is to determine chlorinated solvent contamination levels in an upward flow constructed wetland at Wright-Patterson Air Force Base (WPAFB), Ohio. A stratified grid sampling methodology will be used in sampling the contaminated groundwater. Analysis will be accomplished by means of purge-and-trap gas chromatography. The contaminant concentration levels will be used to enhance the design and construction of man-made wetlands used to remove chlorinated solvents from aquifers. PCE levels declined from an average of 33.97 ppb in the inflow stream to an average of 3.65 ppb in the upper layer, a 91% reduction. High concentrations occurred in areas where high hydraulic pressure gradients and hydraulic conductivities combined to allow contaminated water to migrate to the upper layers of the wetland with minimal contact time for reduction. Removing these areas from the data set increased the PCE reduction efficiency to nearly 98% with an upper level concentration average of 0.84 ppb. Trichloroethene (TCE) inflow rates averaged 0.63 ppb while TCE concentrations in the upper layer averaged 0.175 ppb. TCE concentrations peaked in the middle layer of the wetland suggesting that reduction of PCE was occurring there and in the bottom layer.
Download or read book Quantitative Validation of a Model of Chlorinated Ethene Natural Attenuation written by Harold C. Young and published by . This book was released on 2001-03-01 with total page 95 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chlorinated ethenes are among the most prevalent groundwater contaminants at hazardous waste sites nationwide. In an attempt to manage the risks posed by these contaminants, while controlling costs, monitored natural attenuation (MNA) is being considered as a remediation strategy at many sites. MNA relies on naturally occurring physical, chemical, and biological processes in the subsurface to reduce the risk posed by the contamination. The implementation of MNA, however, requires a detailed understanding of these processes, and how they impact contamination at a particular site. One way to gain this understanding is through contaminant fate and transport modeling. In this study, a deterministic model that includes relevant fate and transport processes was applied to a chlorinated ethene-contaminated field site, at which spatial and temporal data had been collected. Parameters used for model input were obtained from the literature, experimental data, and by calibrating the model using concentration data from 1993. The model was then run in a predictive mode, and simulation results were compared to field data from 1999. Model performance was measured by comparison of observed and simulated concentration contour plots and evaluation of goodness-of-fit statistics. Over the six years the model was run in a predictive mode, the model was found to predict contaminant concentrations reasonably well for the three contaminants that were monitored.
Download or read book Characterization of Chlorinated Solvent Degradation in a Constructed Wetland written by Nathan D. Clemmer and published by . This book was released on 2003-03 with total page 159 pages. Available in PDF, EPUB and Kindle. Book excerpt: Widespread chlorinated ethene contamination of aquifers coupled with high costs of current treatment technologies demand innovative remediation solutions. Wetlands, maintaining anaerobic and aerobic zones promoting the complete degradation of chlorinated ethenes such as Tetrachloroethylene (PCE), could be the answer. This thesis characterized the chlorinated solvent contamination levels in three strata of an upward flow constructed wetland. Analysis of samples was accomplished by purge-and-trap gas chromatography. Water quality parameters, Dissolved Oxygen (DO), Oxidation Reduction Potential (ORP), pH, Conductivity, and Temperature, were also measured in monitoring wells with a water monitoring sonde. After removing data outliers caused by short-circuiting flow, PCE concentrations declined from an average of 32,59 +/- 0,699 ppb (+/- 95% confidence interval) in the inflow stream to an average of 0.171 +/- 0.079 ppb in the upper layer (99,3% reduction). Concentration trends of PCE degradation products cis-1,1 -Dichloroethylene (cis-DCE), Vinyl Chloride (VC), and Trichloroethylene TCE) indicate dechlorination processes are occurring. In addition to PCE, TCE at concentrations below 0,6 ppb was the only other analyte detected in the inflow and outflow, Water quality measurements (DO and 0RP) decreased from the bottom to the middle layer to a level that supports anaerobic reductive dechlorination but not methanogenesis. The DO increased slightly from the middle to the top layer while 0RP continued to decrease.
Download or read book Analysis of Anion Distributions in the Developing Strata of a Constructed Wetland Used for Chlorinated Ethene Remediation written by Joshua D. Kovacic and published by . This book was released on 2003-03 with total page 164 pages. Available in PDF, EPUB and Kindle. Book excerpt: Perchloroethene (PCE), Trichloroethene (TCE) and their degradation products are among the most common organic groundwater contaminants in the United States. Constructed wetlands utilizing upward flow harbor reduction- oxidation conditions that have demonstrated the potential to promote both partial and total mineralization of PCE and TCE through the process of natural attenuation. Organic acid and inorganic anion concentrations are indicative of reduction-oxidation processes that drive chlorinated ethene degradation. These analytes were investigated to assess their development within three vertically stratified regions of a constructed wetland cell at Wright-Patterson Air Force Base fed by groundwater contaminated with PCE and TCE. Data collected during the months of January 2002, December 2002, and January 2003 revealed changes in the organic acid pool over time and in space that correlated with changes in the inorganic anion pool. Overall organic acid concentrations decreased by an average of 93% over 11 month period, indicating a substantial geochemical evolution of the organic acid pool over this time frame. Measurements dissolved oxygen and ORP supported the existence of an aerobic region at the base of the wetland, followed by an anaerobic region in the strata above. Significant nitrate and sulfate reduction in the anaerobic region occurred in unison with the emergence of higher concentrations of lactate and formate. Results indicate the reducing conditions and substrates required to support reductive dechlorination of chlorinated ethenes were present in the subsurface of the wetland.
Download or read book Characterization of Chlorinated Solvent Degradation Profile Due to Microbial and Chemical Processes in a Constructed Wetland written by Teresa A. Sobolewski and published by . This book was released on 2004-03 with total page 97 pages. Available in PDF, EPUB and Kindle. Book excerpt: Perchloroethene (PCE) and its degradation products are among the most common organic groundwater contaminants in the United States. Constructed wetlands are a relatively new approach to dealing with this contamination problem. With their upward flow capability it is possible to introduce an aerobic and anaerobic environment with a consortium of microorganisms available to degrade the contaminants to within acceptable levels established by the Environmental Protection Agency (EPA). This study is a follow-up to the previous two years of research on PCE degradation in cell 1 at Wright-Patterson Air Force Base. This thesis was conducted in order to study the wetland and determine the mechanisms that exist to degrade the chlorinated solvent contamination that is present. It also provided additional evidence that the constructed wetland is degrading PCE to its innocuous byproducts. A purge-and-trap gas chromatograph was used to determine the concentrations of PCE, TCE, DCE isomers, and VC throughout the three layers of the constructed wetland. Inflow and outflow were also sampled and analyzed. In this year's data, PCE was detected at a level that was below the maximum contaminant level established by the EPA. However, it is clear that Cell 1 is still developing. This wetland cell has been in existence for three years and it is obvious that the development of a constructed wetland is a lengthy process. If a constructed wetland were to be used as a treatment process for contaminated water sources, time would have to be allowed for it to develop before it would reach maximum treatment efficiency.
Download or read book Simulation and Optimization of a Constructed Wetland for Biomass Production and Nitrate Removal written by Aras J. Zygas and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Recently there is growing concern about high nutrient loadings in surface waters as a result of intensive agriculture, resulting in hypoxia in costal ecosystems. There is simultaneous growing interest in the cultivation of perennial grasses for bio-ethanol production. Constructed wetlands offer a promising nutrient removal mechanism while also providing an ideal environment for the growth of such grasses. In the present work, a hypothetical wetland system is designed to treat non-point source nutrient loadings and produce harvestable biomass for ethanol production in central Illinois. Through the integration of a biomass production model, a nutrient removal model and a cost model, the relationship between the costs of wetland construction, benefits from biomass sales, and mass nutrient removal can be seen for various wetland sizes and water throughput capacities. Using genetic algorithms, the Pareto-optimal frontier showing the tradeoff between nutrient removal and the net cost of the wetland system, (accounting for revenue from biomass harvest) can be visualized. This analysis is demonstrated for a hypothetical wetland site near Camargo, Illinois which is assumed to draw water from the Embarras River. Through the simulation of several cost scenarios, the wetland is found to show a profit only when construction, operation and maintenance costs are excluded from the analysis. Results show a tradeoff between the amount of nitrate removed in the wetland via denitrification and biomass production For the example case, a 33.8 ha wetland with a 2.3 m3/s design pumping capacity was found to have the maximum cost efficiency with a cost of 4.8 $/kg of NO3-N removed. The results indicate that there is a unique efficiency-maximizing design for a wetland at a particular site. These results also indicate that a subsidy of at least 4.8 $/kg of NO3-N removed is necessary (assuming the biomass is sold for $58/ton) in order for a wetland at the hypothetical site to break even. Furthermore, if a market for nitrogen exists or if nutrient trading between point dischargers is allowed, it might be possible for a constructed wetland designed for biomass production to be profitable while providing water quality benefits.
Download or read book Biogeochemistry of Wetlands written by K. Ramesh Reddy and published by CRC Press. This book was released on 2022-09-10 with total page 926 pages. Available in PDF, EPUB and Kindle. Book excerpt: The globally important nature of wetland ecosystems has led to their increased protection and restoration as well as their use in engineered systems. Underpinning the beneficial functions of wetlands are a unique suite of physical, chemical, and biological processes that regulate elemental cycling in soils and the water column. This book provides an in-depth coverage of these wetland biogeochemical processes related to the cycling of macroelements including carbon, nitrogen, phosphorus, and sulfur, secondary and trace elements, and toxic organic compounds. In this synthesis, the authors combine more than 100 years of experience studying wetlands and biogeochemistry to look inside the black box of elemental transformations in wetland ecosystems. This new edition is updated throughout to include more topics and provide an integrated view of the coupled nature of biogeochemical cycles in wetland systems. The influence of the elemental cycles is discussed at a range of scales in the context of environmental change including climate, sea level rise, and water quality. Frequent examples of key methods and major case studies are also included to help the reader extend the basic theories for application in their own system. Some of the major topics discussed are: Flooded soil and sediment characteristics Aerobic-anaerobic interfaces Redox chemistry in flooded soil and sediment systems Anaerobic microbial metabolism Plant adaptations to reducing conditions Regulators of organic matter decomposition and accretion Major nutrient sources and sinks Greenhouse gas production and emission Elemental flux processes Remediation of contaminated soils and sediments Coupled C-N-P-S processes Consequences of environmental change in wetlands# The book provides the foundation for a basic understanding of key biogeochemical processes and its applications to solve real world problems. It is detailed, but also assists the reader with box inserts, artfully designed diagrams, and summary tables all supported by numerous current references. This book is an excellent resource for senior undergraduates and graduate students studying ecosystem biogeochemistry with a focus in wetlands and aquatic systems.
Download or read book Characterization of Microbial Processes that Degrade Chlorinated Solvents in a Constructed Wetland Using Organic Acid and Inorganic Anion Concentration Profiles written by and published by . This book was released on 2004-03 with total page 113 pages. Available in PDF, EPUB and Kindle. Book excerpt: Chlorinated solvents have been used in industrial cleaning and degreasing processes in the United States since the early 1900s, and their induction into the environment increased significantly with the growth of industrial processes over the past century. PCE, TCE and their daughter products have been associated with a number of human health concerns and are currently the most common contaminants found in groundwater in the United States. Wetlands possess characteristics necessary for the complete degradation of chlorinated ethenes by microorganisms via anaerobic and aerobic regions that foster the necessary oxidation-reduction conditions. Organic acid and inorganic anion concentrations were evaluated in samples taken from a constructed wetland at Wright-Patterson Air Force Base, Ohio during the summer and fall of 2003. These analyses are indicative of redox conditions in the subsurface and suggest the occurrence of microbial activities that degrade chlorinated ethenes to innocuous end products. Organic acid concentrations decreased by 100% from July 2003 to fall 2003. Combined with data collected previously during the months of December and January, this suggested that changing seasons and temperature fluctuations have a significant influence on microbial metabolisms. Nitrate and sulfate reduction above stratum C indicated mildly reducing conditions in the lowest stratum that became more highly reducing in the upper two strata. Based on the changing analyst concentrations throughout the wetland cell over several seasons, it was evident that the appropriate subsurface conditions existed for the reductive dechlorination of chlorinated ethenes.
Download or read book Onsite Wastewater Treatment Systems Manual written by and published by . This book was released on 2002 with total page 378 pages. Available in PDF, EPUB and Kindle. Book excerpt: "This manual contains overview information on treatment technologies, installation practices, and past performance."--Introduction.
