1,721,053 research outputs found
Characterizing toluene adsorption onto carbon nanotubes for environmental applications
No full textTwo different types of carbon nanotubes (CNTs), multi-walled and single-walled carbon nanotubes (MWCNTs and SWCNTs, respectively), have been characterized as new potential sorbents for contaminant removal from aqueous phase and can be used through different technological implementations. The performance of the materials has been evaluated in comparison with the most commonly used carbonaceous material, activated carbon (AC). Adsorption properties were evaluated by kinetic and equilibrium batch tests in aqueous solution at different salinity levels. Toluene was chosen as the reference compound to simulate the water phase dissolved portion of an oil spill. The experimental results have clearly demonstrated faster motion and higher adsorption capacity of MWCNTs and SWCNTs compared with AC. CNTs have shown very high removal efficiency for dissolved toluene, up to 30% and 90% for MWCNTs and SWCNTs, respectively. These results are very promising for the prospective use of CNTs as a potential alternative sorbent for hydrophobic organic compound (HOC) removal in environmental applications. © 2017 Desalination Publications. All rights reserved
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Bioavailability and trophic transfer of PAHs and PCBs
No full textEnvironmental and Water Resources Engineerin
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Evaluating sediment cap performance with PDMS profilers : field study of McCormick and Baxter Superfund Site
Full text linktextDuring the Fall of 2009, a pilot study was conducted at the McCormick and Baxter (M&B) Superfund Site to evaluate polydimethylsiloxane (PDMS) profilers as a method for sediment cap performance monitoring. The profilers are shielded solid phase microextraction fibers, silica rods coated with polydimethylsiloxane (PDMS) as the sorbent. The deployment explored whether profiling PDMS could be used as a low impact, highly sensitive, long term monitoring strategy at M&B since the sediment operable unit will be transitioning to the “Operable & Maintenance” phase of Superfund cleanup.
To evaluate sediment cap performance, a good understanding of the flux of contaminants from the sediment is required. While surface waters can illustrate this flux, they can also contain contaminants originating from upstream sources. The existing sampling plan at M&B uses a conventional porewater pumping sampling technique that measures both dissolved and particulate fractions. PDMS profilers measure only the freely dissolved fraction which has been shown to be a good indicator of bioavailability. These profilers also have lower detection limits (ng/L) and the ability to measure vertical concentration gradients which can help identify sources and mechanisms of the contamination.
Each sampler was analyzed at three depths for the USEPA Priority Pollutant List of 16 polycyclic aromatic hydrocarbons (PAHs). PDMS measurements showed clear vertical profiling with large reductions in PAH concentrations through the sediment cap offshore. Nearshore, uniform concentration profiles were observed indicating increased vertical mixing as a result of tidal smearing. Further, ANOVA and Tukey-Kramer HSD analysis of sample variability revealed PAH concentrations were statistically different at two locations compared to the remainder of the sampling locations- indicating areas requiring closer attention.
PDMS profilers were co-located at 13 of the 22 conventional porewater extraction sampling locations. The correlation of PDMS and conventional porewater extraction techniques was limited due to the low detection frequency by conventional porewater extraction methods as a result of the higher detection limits by that method. The correlation was good for light molecular weight PAHs with most measurements of the same order of magnitude and improved with increasing depth (due to the greater number of detections). 72% of the direct comparisons between PDMS-derived and conventionally-derived porewater concentrations were of the same order of magnitude. Any comparison between the two datasets is necessarily limited especially for the higher molecular weight PAHs, however, due to the large number of non-detects in the conventionally collected data.Civil, Architectural, and Environmental Engineerin
PRELIMINARY ASSESSMENT OF CHLOROBENZENES FATE AND TRANSPORT IN SEDIMENT ENVIRONMENT
No full textChlorobenzenes are omnipresent environmental pollutants due to their widespread use as a chemical intermediate and solvent. Sediment from a specific site was characterized for monochlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene and 1,2,4-trichlorobenzene contamination. Adsorption of Chlorobenzenes on commercially available sorbents such as activated carbon (AC), biochar, and organophilic clay were investigated for their potential use for in-situ management and active capping of Chlorobenzene-contaminated sediment. The results show that sorption on AC follows the Freundlich isotherm model whereas, organophilic clay, and biochar exhibit linear sorption properties. AC was found the most sorbing compared to biochar and organophilic clay by about two and four orders of magnitude, respectively. In addition, AC was most affected by natural organic matter (NOM) fouling; the effect of NOM on biochar and organophilic clay was minimal. Data from these studies were used to simulate Chlorobenzenes flux under existing field conditions, as well as, the performance of caps amended with AC, biochar, and organophilic clay. The modeling was done for diffusion control, diffusion-advection (Darcy’s velocity 1 cm/day) and tidal flow system (tidal cycle 12 hours 25 minutes with maximum tidal flow of 100 cm/yr). The effect of bioturbation was also considered. Simulation results suggest that the system with the presence of diffusion-advection is the most critical in terms of flux breakthrough from caps. Only AC amended caps were found to be effective to contain the contaminants for considerable amount of time. The breakthrough time for 15 cm AC layer with 15 cm sand on top and 50% AC amended sand cap is simulated to be about 100 years.Embargo status: Restricted until 09/2166. To request the author grant access, click on the PDF link to the left
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Zero-valent iron's effectiveness at dehalogenating chlorobenzenes and its feasibility as a reactive cap
No full texttextThrough the deliberate or inadvertent release to the environment, contaminants have polluted the nation's waterways leaving a residual of refractory pollutants that reside in sediments. The Bayou d'Inde is a tributary of the Calcasieu River outside Lake Charles, Louisiana that has been contaminated by several industrial pollutants including hexachlorobenzene (HCB). Due to HCB's high organic carbon partition coefficient (Koc), its availability to reducing microorganisms is extremely limited and natural attenuation has been found to be ineffective at reducing HCB concentrations in-situ. The effectiveness of an active cap is being evaluated to reduce contaminant flux to the benthos and water column. This study was designed to explore the fate of chlorinated benzenes during capping of the contaminated sediment, specifically the fate associated with zero-valent iron in an active capping layer. Experiments exploring the degradation of chlorinated benzenes with mirco-scale and nano-scale zero-valent iron and the potential for zero-valent iron as an active capping material to encourage dechlorination under environmentally relevant and ideal conditions were carried out. Less than 1% of the chlorinated benzenes were observed to dechlorinate within 48 hours by micro-scale zero-valent iron and transport through a 1.25 cm thick CETCO mat would dechlorinate 8% of the mobile hexachlorobenzene before release to the water column. That is why zero-valent iron should not be employed as an active capping material in the Bayou d'Inde for the purposes of reductively dechlorinating chlorinated benzenes.Environmental and Water Resources Engineerin
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Passive sampling to evaluate performance of in situ sediment remediation
Full text linktextIn situ passive sampling is the use of a polymer sorbent to directly assess freely dissolved concentration (C [subscript free]) profiles within the environment. The primary focus herein is the use of passive sampling methods to detect and quantify persistent hydrophobic organic compounds (HOCs) in sediment porewater and surface water using solid phase microextraction (SPME) profilers with polydimethylsiloxane (PDMS) as the receiving phase sorbent. Contaminated sediment sites pose a unique challenge in terms of remediation and monitoring for several reasons including: the large number of past and ongoing sources, sediment stability, and the extent of contamination. Capping with a clean layer of material, an accepted remediation approach, can reduce risk by stabilizing the underlying sediments, isolating the water column, and reducing contaminant flux. Evaluating cap performance is challenging due to the long time frames associated with migration of HOCs. Additionally, the non-sorbing nature of most caps limits the usefulness of bulk solid measurements. An alternative is the use of concentrations in the interstitial space or porewater to examine contaminant migration in the sediments and cap. Traditionally, porewater concentrations are obtained through a conversion of bulk sediment concentrations using an assumed sediment-water partitioning coefficient. This assumption often leads to a misrepresentation of risk as not all organic carbon is created equal. An alternative is the use of passive sampling with polymer sorbents to estimate the freely available concentration, C [subscript free]. In this work the focus is on the use of solid phase microextraction with polydimethylsiloxane (SPME PDMS) as the sorbent. C [subscript free] is proportional to chemical activity; therefore an accurate measurement of C [subscript free] is necessary for risk assessment and determination of transport mechanisms and ultimately improved management of contaminated sediment sites. A non-equilibrium correction protocol using performance reference compounds (PRCs) was developed to enhance the accuracy of the SPME PDMS method to assess C [subscript free]. The protocol was validated through laboratory experiments and field trials. Deployment times can be reduced without sacrificing accuracy when using the PRC protocol. Furthermore, it was shown that mathematical models of diffusive and advective flux can be fit using parameters determined from PRC desorption. The SPME PDMS with PRCs method was used at three different remediated contaminated sediment sites, Chattanooga Creek, Eagle Harbor, and the West Branch of the Grand Calumet River, to illustrate its utility at evaluating performance of in situ remediation. Overall, the results from laboratory and field studies suggest that SPME PDMS is a valuable tool for evaluating performance of in situ sediment remediation.Civil, Architectural, and Environmental Engineerin
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Effects of bioturbation on the bacterial community in contaminated sediment
No full textBioturbation has been shown to expedite the degradation of refractory compounds in contaminated sediments. In an effort to determine whether bioturbation influences sediment bacterial community diversity, a river simulation was operated in microcosm cells with sediment samples from the Anacostia River (Washington D.C.). Sample cells contained the freshwater oligochaete Ilyodrilus templetoni at a density of 20,000 / m² while control cells were operated without benthic organisms. Vertical profiles of redox potential, sulfide, and dissolved oxygen concentrations were determined during river simulations. As compared to the condition without macrobenthos, Ilyodrilus expedited oxygen consumption and lowered the redox potential in the top four centimeters of sediment. Sulfide concentrations were below the limit of detection. After five months the cells were extruded and analyzed by layer for select microbial parameters. Bacteria were quantified by direct count and communities were profiled at different depths using denaturing gradient gel electrophoresis (DGGE).Environmental and Water Resources Engineerin
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The interaction of benthic oligochaetes, T. tubifex with mercury impacted sediments: an assessment of bioaccumulation and biogeochemistry
Full text linktextMercury is a pervasive environmental contaminant which is globally distributed in freshwater ecosystems. In order to assess the risk that mercury and methylmercury pose to public health through consumption and trophic level transfer, it is first necessary to understand the interactions and uptake that occurs between benthic organisms and mercury impacted sediments. Delineation of these interactions currently rely on correlating measurements of bulk sediment concentrations with bioaccumulation of either total mercury or methylmercury. However, it has been proposed that porewater concentrations, rather than sediment concentrations, should be used to predict uptake and bioavailability. Diffusive gradient in thin films (DGTs) have been proposed as a viable technique for porewater measurements to assess the bioavailable fractions of mercury. DGTs were compared to traditional bulk solid sampling to assess their capabilities for the prediction of total and methylmercury bioaccumulation in benthic oligochaetes, T. tubifex. DGTs performed similarly to the bulk solids sampling approach in respect to their correlation with mercury bioaccumulation in the sediment matrix studied. Bioturbation was shown to impact redox profiles in the sediment which led to a decrease in porewater methylmercury concentrations in the uppermost surficial sediment depths. These results indicate that monitoring tools such as DGTs are necessary to better understand the fate of mercury at field scale contaminated sites.Environmental and Water Resources Engineerin
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Laboratory study of calcium based sorbents impacts on mercury bioavailability in contaminated sediments
Full text linktextMercury -contaminated sediments often act as a sink of mercury and produce methyl-mercury, an acute neurotoxin which readily bio accumulates, due to the presence of bacterial communities hosted by the sediment. One common remediation approach to manage methyl-mercury is to amend the sediment by capping or directly mixing with a sorbent. This thesis aims to assess the capabilities of some calcium-based sorbent to act in that capacity. Laboratory experiments were implemented to simulate mercury fate and behavior in geochemical conditions that capping would likely create. Well-mixed slurries showed that gypsum materials were disparate and their behavior was similar from sand to organocaly. Mercury sorption capacities of these gypsums were poor with a sorption coefficient approximately equal to 300 L/kg. Reduction of methylmercury was minimal and even increased in two of the three materials. Therefore, the three gypsums, which tend to be more cohesive when wetted, doesn’t constitute a viable material for sediment capping.Civil, Architectural, and Environmental Engineerin
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Evaluating organic compound sorption to several materials to assess their potential as amendments to improve in-situ capping of contaminated sediments
Full text linktextContaminated sediments represent a common environmental problem because they can sequester large quantities of contaminants which can remain long after the source of pollution has been removed. From the sediment these hazardous compounds are released into the sediment porewater where it can partition into organisms in the sediment and bioaccumulate up the food web; leading to an ecological and human health concern. The objective of this work is to investigate an emerging option in contaminated sediment remediation; specifically an option for in-situ treatment known as active capping. Conventional capping uses clean sediment or sands to separate contaminated sediment from overlying water and biota. Active capping is the use of a sorptive amendment to such a cap to improve its effectiveness.
This work focuses on granular materials as direct amendments to conventional caps including; granular activated carbon (GAC), iron/palladium amended GAC, alumina pillared clay, rice husk char, and organically modified clays. All materials were investigated in batch sorption tests of benzene, chlorobenzene, and naphthalene in DI water. Additionally porewaters from three sites were extruded and the concentrations of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) were measured. At Manistique Harbor and Ottawa River PCBs were identified as the primary contaminant of concern while PAHs were the contaminant of concern at the Grand Calumet River. At these sites a solvent extraction method was used to analyze the sediment concentrations of the contaminants of concern. From the former batch tests activated carbon and a commercially available organoclay were chosen for further investigation. This includes PAHs in batch sorption tests using extruded sediment porewater to investigate matrix effects, and PCB sorption in distilled water.Civil, Architectural, and Environmental Engineerin
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