Download Free Characterization Of Microbial Processes That Degrade Chlorinated Solvents In A Constructed Wetland Using Organic Acid And Inorganic Anion Concentration Profiles Book in PDF and EPUB Free Download. You can read online Characterization Of Microbial Processes That Degrade Chlorinated Solvents In A Constructed Wetland Using Organic Acid And Inorganic Anion Concentration Profiles and write the review.

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.
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.
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.
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.
V.3 ... consists of individual chapters that describe 1) the conceptual background for radionuclides, including tritium, radon, strontium, technetium, uranium, iodine, radium, thorium, cesium, plutonium-americium and 2) data requirements to be met during site characterization.
Constructed wetlands (CWs) are ecologically-based water treatment systems that provide cost-effective amelioration of waterborne pollutants. Fundamental understanding of removal mechanisms, especially microbial processes, limits greater usage of constructed wetlands as a wastewater treatment system. The influence of plant species selection, season, and organic load rate on pollutant removal was previously linked to the redox condition of the sub-surface wetland environment. The goal of this research was to determine which of these environmental variables (including spatial location within the CW) influenced the dominant microbial populations and/or the activity of various sub-populations. Once identified, a constructed wetland might be optimized for growth of microorganisms involved in removal of a specific pollutant. To assess environmental factors, microbial population samples were taken in six locations (effluent, 3 root and 2 gravel areas) within replicate unplanted microcosms and wetland microcosms planted with Deschampsia cespitosa or Leymus cinereus during the summer (24°C) and winter (4°C) seasons. Microcosms were fed a synthetic domestic wastewater in 20-day batches for at least 12 months prior to sampling. The most recent techniques in molecular biology including denaturing gradient gel electrophoresis (DGGE) and quantitative PCR were utilized and included treatment with and without propidium monoazide (PMA) to distinguish between "live" and "dead" microbial communities. Primer sets targeted the entire bacterial community (16S rDNA) and two functional groups, nitrifying bacteria (amoA gene) and sulfate reducing bacteria (dsrB gene). Results indicated that overall microbial community structure (16S rDNA) was affected by general location within the microcosm (effluent, root, gravel) as well the plant species present. Specific microbial groups appeared to be affected differently with relative gene quantities of sulfate reducing bacteria and nitrifying bacteria being influenced by a combined effect of plant species and season. For dsrB, D. cespitosa had the lowest relative gene quantities overall. Both genes were more abundant in the summer season, indicating seasonal importance. Location within the microcosms was also important, with anoxic environments (column bottom) being more important for dsrB presence and a diverse population of cultivated sulfate reducers. The roots were an important location for both microbial diversity and activity for all genes investigated.
Proceedings of the 42nd OHOLO Conference held in Eilat, Israel, May 3-7, 1998