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Port Hueneme, CA, United States

Topham N.,University of Florida | Wang J.,University of Florida | Kalivoda M.,University of Florida | Huang J.,University of Florida | And 7 more authors.
Annals of Occupational Hygiene | Year: 2012

Hexavalent chromium (Cr 6+) emitted from welding poses serious health risks to workers exposed to welding fumes. In this study, tetramethylsilane (TMS) was added to shielding gas to control hazardous air pollutants produced during stainless steel welding. The silica precursor acted as an oxidation inhibitor when it decomposed in the high-temperature welding arc, limiting Cr 6+ formation. Additionally, a film of amorphous SiO2 was deposited on fume particles to insulate them from oxidation. Experiments were conducted following the American Welding Society (AWS) method for fume generation and sampling in an AWS fume hood. The results showed that total shielding gas flow rate impacted the effectiveness of the TMS process. Increasing shielding gas flow rate led to increased reductions in Cr 6+ concentration when TMS was used. When 4.2% of a 30-lpm shielding gas flow was used as TMS carrier gas, Cr 6+ concentration in gas metal arc welding (GMAW) fumes was reduced to below the 2006 Occupational Safety and Health Administration standard (5 μg m -3) and the efficiency was >90%. The process also increased fume particle size from a mode size of 20 nm under baseline conditions to 180-300 nm when TMS was added in all shielding gas flow rates tested. SiO2 particles formed in the process scavenged nanosized fume particles through intercoagulation. Transmission electron microscopy imagery provided visual evidence of an amorphous film of SiO2 on some fume particles along with the presence of amorphous SiO2 agglomerates. These results demonstrate the ability of vapor phase silica precursors to increase welding fume particle size and minimize chromium oxidation, thereby preventing the formation of hexavalent chromium. © The Author 2011. Source

Johnson P.C.,Arizona State University | Bruce C.L.,Global Solutions U.S. Inc. | Miller K.D.,Engineering Service Center
Ground Water Monitoring and Remediation | Year: 2010

A paradigm for the design, monitoring, and optimization of in situ methyl tert-butyl ether (MTBE) aerobic biobarriers is presented. In this technology, an oxygen-rich biologically reactive treatment zone (the "biobarrier") is established in situ and downgradient of the source of dissolved MTBE contamination in groundwater, typically gasoline-impacted soils resulting from leaks and spills at service station sites or other fuel storage and distribution facilities. The system is designed so that groundwater containing dissolved MTBE flows to, and through, the biobarrier treatment zone, ideally under natural gradient conditions so that no pumping is necessary. As the groundwater passes through the biobarrier, the MTBE is converted by microorganisms to innocuous by-products. The system also reduces concentrations of other aerobically degradable chemicals dissolved in the groundwater, such as benzene, toluene, xylenes, and tert-butyl alcohol. This design paradigm is based on experience gained while designing, monitoring, and optimizing pilot-scale and full-scale MTBE biobarrier systems. It is largely empirically based, although the design approach does rely on simple engineering calculations. The paradigm emphasizes gas injection-based oxygen delivery schemes, although many of the steps would be common to other methods of delivering oxygen to aquifers. © 2009 National Ground Water Association. Source

Capiro N.L.,Tufts University | Granbery E.K.,Georgia Institute of Technology | Lebron C.A.,Engineering Service Center | Major D.W.,Geosyntec Consultants | And 6 more authors.
Environmental Science and Technology | Year: 2011

A combination of batch and column experiments evaluated the mass transfer of two candidate partitioning electron donors (PEDs), n-hexanol (nHex) and n-butyl acetate (nBA), for enhanced bioremediation of trichloroethene (TCE)-dense nonaqueous phase liquid (DNAPL). Completely mixed batch reactor experiments yielded equilibrium TCE-DNAPL and water partition coefficients (KNW) for nHex and nBA of 21.7 ± 0.27 and 330.43 ± 6.7, respectively, over a range of initial PED concentrations up to the aqueous solubility limit of ca. 5000 mg/L. First-order liquid-liquid mass transfer rates determined in batch reactors with nBA or nHex concentrations near the aqueous solubility were 0.22 min-1 and 0.11 min-1, respectively. Liquid-liquid mass transfer under dynamic flow conditions was assessed in one-dimensional (1-D) abiotic columns packed with Federal Fine Ottawa sand containing a uniform distribution of residual TCE-DNAPL. Following pulse injection of PED solutions at pore-water velocities (vp) ranging from 1.2 to 6.0 m/day, effluent concentration measurements demonstrated that both nHex and nBA partitioned strongly into residual TCE-DNAPL with maximum effluent levels not exceeding 35% and 7%, respectively, of the applied concentrations of 4000 to 5000 mg/L. PEDs persisted at effluent concentrations above 5 mg/L for up to 16 and 80 pore volumes for nHex and nBA, respectively. Mathematical simulations yielded KNW values ranging from 44.7 to 48.2 and 247 to 291 and liquid-liquid mass transfer rates of 0.01 to 0.03 min-1 and 0.001 to 0.006 min-1for nHex and nBA, respectively. The observed TCE-DNAPL and water mass transfer behavior suggests that a single PED injection can persist in a treated source zone for prolonged time periods, thereby reducing the need for, or frequency of, repeated electron donor injections to support bacteria that derive reducing equivalents for TCE reductive dechlorination from PED fermentation. © 2011 American Chemical Society. Source

Ritalahti K.M.,University of Tennessee at Knoxville | Hatt J.K.,Georgia Institute of Technology | Lugmayr V.,University of Tennessee at Knoxville | Henn K.,Tetra Tech Inc. | And 7 more authors.
Environmental Science and Technology | Year: 2010

Biostimulation and bioaugmentation have emerged as constructive remedies for chlorinated ethene-contaminated aquifers, and a link between Dehalococcoides (Dhc) bacteria and chlorinated ethene detoxification has been established. To quantify Dhc biomarker genes, groundwater samples are shipped to analytical laboratories where biomass is collected on membrane filters by vacuum filtration for DNA extraction and quantitative real-time PCR analysis. This common practice was compared with a straightforward, on-site filtration approach to Sterivex cartridges. In initial laboratory studies with groundwater amended with known amounts of Dhc target cells, Sterivex cartridges yielded one-third of the total DNA and 9-18% of the Dhc biomarker gene copies compared with vacuum filtration. Upon optimization, DNA yields increased to 94 ± 38% (±SD, n = 10), and quantification of Dhc biomarker genes exceeded the values obtained with the vacuum filtration procedure up to 5-fold. Both methods generated reproducible results when volumes containing >104 total Dhc target gene copies were collected. Analysis of on-site and off-site biomass collection procedures corroborated the applicability of the Sterivex cartridge for Dhc biomarker quantification in groundwater. Ethene formation coincided with Dhc cell titers of >2×106 L1 and high (i.e., >105) abundance of the vinyl chloride reductive dehalogenase genes vcrA and/or bvcA; however, high Dhc cell titers alone were insufficient to predict ethene formation. Further, ethene formation occurred at sites with high Dhc cell titers but low or no detectable vcrA or bvcA genes, suggesting that other, not yet identified vinyl chloride reductive dehalogenases contribute to ethene formation. On-site biomass collection with Sterivex cartridges avoids problems associated with shipping groundwater and has broad applicability for biomarker monitoring in aqueous samples. © 2010 American Chemical Society. Source

Hatt J.K.,Georgia Institute of Technology | Ritalahti K.M.,University of Tennessee at Knoxville | Ogles D.M.,Microbial Insights Inc | Lebron C.A.,Engineering Service Center | And 2 more authors.
Environmental Science and Technology | Year: 2013

Dehalococcoides mccartyi (Dhc) strains are keystone bacteria for reductive dechlorination of chlorinated ethenes to nontoxic ethene in contaminated aquifers. Enumeration of Dhc biomarker genes using quantitative real-time PCR (qPCR) in groundwater is a key component of site assessment and bioremediation monitoring. Unfortunately, standardized qPCR procedures that recognize impaired measurements due to PCR inhibition, low template DNA concentrations, or analytical error are not available, thus limiting confidence in qPCR data. To improve contemporary approaches for enumerating Dhc in environmental samples, multiplex qPCR assays were designed to quantify the Dhc 16S rRNA gene and one of two different internal amplification controls (IACs): a modified Dhc 16S rRNA gene fragment (Dhc*) and the firefly luciferase gene luc. The Dhc* IAC exhibited competitive inhibition in qPCR with the Dhc 16S rRNA gene template when the ratio of either target was 100-fold greater than the other target. A multiplex qPCR assay with the luc IAC avoided competitive inhibition and accurately quantified Dhc abundances ranging from ∼10 to 107 16S rRNA gene copies per reaction. The addition of ∼106 E. coli luc IAC to simulated groundwater amended with the Dhc-containing consortium KB-1 yielded reproducible luc counts after DNA extraction and multiplex qPCR enumeration. The application of the luc IAC assay improved Dhc biomarker gene quantification from simulated groundwater samples and is a valuable approach for "ground truthing" qPCR data obtained in different laboratories, thus reducing ambiguity associated with qPCR enumeration and reproducibility. © 2013 American Chemical Society. Source

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