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61.
Reductive dechlorination of trichloroethene (TCE) by zero-valent iron produces a systematic enrichment of 13C in the remaining substrate that can be described using a Rayleigh model. In this study, fractionation factors for TCE dechlorination with iron samples from two permeable reactive barriers (PRBs) were established in batch experiments. Samples included original unused iron as well as material from a barrier in Belfast after almost 4 years of operation. Despite the variety of samples, carbon isotope fractionations of TCE were remarkably similar and seemed to be independent of iron origin, reaction rate, and formation of precipitates on the iron surfaces. The average enrichment factor for all experiments was -10.1 per thousand (+/- 0.4 per thousand). These results indicate that the enrichment factor provides a powerful tool to monitor the reaction progress, and thus the performance, of an iron-reactive barrier over time. The strong fractionation observed may also serve as a tool to distinguish between insufficient residence time in the wall and a possible bypassing of the wall by the plume, which should result in an unchanged isotopic signature of the TCE. Although further work is necessary to apply this stable isotope method in the field, it has potential to serve as a unique monitoring tool for PRBs based on zero-valent iron.  相似文献   
62.
This paper evaluates the importance of seven types of parameters to virus transport: hydraulic conductivity, porosity, dispersivity, sorption rate and distribution coefficient (representing physical-chemical filtration), and in-solution and adsorbed inactivation (representing virus inactivation). The first three parameters relate to subsurface transport in general while the last four, the sorption rate, distribution coefficient, and in-solution and adsorbed inactivation rates, represent the interaction of viruses with the porous medium and their ability to persist. The importance of four types of observations to estimate the virus-transport parameters are evaluated: hydraulic heads, flow, temporal moments of conservative-transport concentrations, and virus concentrations. The evaluations are conducted using one- and two-dimensional homogeneous simulations, designed from published field experiments, and recently developed sensitivity-analysis methods. Sensitivity to the transport-simulation time-step size is used to evaluate the importance of numerical solution difficulties. Results suggest that hydraulic conductivity, porosity, and sorption are most important to virus-transport predictions. Most observation types provide substantial information about hydraulic conductivity and porosity; only virus-concentration observations provide information about sorption and inactivation. The observations are not sufficient to estimate these important parameters uniquely. Even with all observation types, there is extreme parameter correlation between porosity and hydraulic conductivity and between the sorption rate and in-solution inactivation. Parameter estimation was accomplished by fixing values of porosity and in-solution inactivation.  相似文献   
63.
The utility of intrinsic and extant kinetic parameters for simulating the dynamic behavior of a biotreatment system coupled with a distributed, unstructured, balanced microbial growth model were evaluated against the observed response of test reactors to transient loads of synthetic organic compounds (SOCs). Biomass from a completely mixed activated-sludge (CMAS) system was tested in fed-batch reactors, while a sequencing batch reactor (SBR) was tested by measuring SOC concentrations during the fill and react period. Both the CMAS system and the SBR were acclimated to a feed containing biogenic substrates and several SOCs, and the transient loading tests were conducted with biogenic substrates along with one or more SOCs. Extant parameters more closely reflect the steady-state degradative capacity of activated-sludge biomass than intrinsic parameters and, hence, were expected to be better predictors of system performance. However, neither extant nor intrinsic parameters accurately predicted system response and neither parameter set was consistently superior to the other. Factors that may have contributed to the inability of the model to predict system response were identified and discussed. These factors included the role of abiotic processes in SOC removal, disparity in the bases used to evaluate parameter estimates (substrate mineralization) and reactor performance (substrate disappearance), inhibitory substrate interactions under the severe loading conditions of the SBR, changes in the physiological state of the biomass during the transient loading tests, and the presumed correlation between the competent biomass concentration and the influent SOC concentration.  相似文献   
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Meeting the manifold challenges connected to climate change makes high demands on individual competencies. To prepare actors for those challenges learning settings are needed in higher education that are suitable for that goal. A theoretical framework for relevant key competencies can be found in the discourse of Education for Sustainable Development (ESD). In this paper we introduce and discuss two learning settings that employ adapted sustainability science approaches: the syndrome approach and scenario analysis. Both approaches are discussed with reference to their didactic goals to foster the acquisition of the corresponding competencies. The usefulness of these two approaches in creating appropriate learning settings is demonstrated in empirical studies.  相似文献   
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Active sediment caps are being considered for addressing contaminated sediment areas in surface‐water bodies. A demonstration of an active cap designed to reduce advective transport of contaminants using AquaBlok® (active cap material) was initiated in a small study area of the Anacostia River in Washington, D.C. The cap remained physically stable, demonstrated the ability to divert groundwater flow, and was recolonized with native organisms after 30 months of monitoring following cap placement. However, the long‐term performance of active caps associated with harsh environmental conditions, hydrogeological settings, and subsurface gas production needs to be further evaluated. © 2008 Wiley Periodicals, Inc.  相似文献   
68.
The availability of heavy metals in contaminated sediment evaluated for beneficial reuse, before and after chemical amendment, was evaluated using poultry manure as the amendment. The dredged sediment was only slightly contaminated with heavy metals. Availability tests on the amended sediment showed an increase in heavy metals, most likely because of poultry feed amendments passed to the manure. There would be difficulty finding one chemical amendment to reduce the availability of a number of heavy metals because the metals exhibit different chemical properties. © 2001 John Wiley & Sons, Inc.  相似文献   
69.
The intentional dissemination of Bacillus anthracis (anthrax) spores at multiple locations in the United States in the fall of 2001 resulted not only in several deaths and illnesses (including psychological effects), but likely changed lifestyles and attitudes, and increased the public's awareness of individual vulnerability. While federal resources had previously been committed to preparing local public health agencies for counter‐terrorism activities and to enhance environmental and medical response, these release episodes have increased the consistency of environmental and medical response activities, and increased government resources for homeland security. This article abstracts current information from many sources that summarize the environmental responses to the anthrax releases. The article discusses the international agreements and the U.S. regulations concerning biological weapons, the characteristics of the anthrax organism, potential exposure pathways, adverse health conditions resulting from inhalation exposure, the environmental response to two specific release episodes, environmental sampling and analytical procedures, recommended personal protective equipment, and the subsequent federal efforts to improve response capabilities. © 2003 Wiley Periodicals, Inc.  相似文献   
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