Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.23.17 (PCE)
 1,301 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Three low-volume mini-sprinklers were tested for their efficacy to strip trichloroethylene (TCE) and tetrachloroethylene (PCE) from water. Deionized water spiked with TCE and PCE was pumped for approximately 1 h at 0.19 to 0.21 MPa (28 to 30 lb in(-2)) through a mini-sprinkler supported on top of a 1.8-m-tall riser. Water was collected in collection vessels at 0.61 and 1.22 m above the ground on support columns that were spaced at 0.61-m intervals from the riser base, and samples were composited per height and distance from the riser. Overall, air-stripping reduced dissolved concentrations of TCE and PCE by 99.1 to 100 and 96.9 to 100%, respectively, from mean influent dissolved concentrations of 466 to 1675 microg L(-1) TCE and 206 to 940 microg L(-1) PCE. In terms of mass removed, the mini-sprinklers removed TCE and PCE at a rate of approximately 1400 to 1700 and 700 to 900 microg L(-1), respectively, over a 1-h test period. Mini-sprinklers offer the advantages of (i) easy setup in series that can be used on practically any terrain; (ii) operation over a long period of time that does not threaten aquifer depletion; (iii) use in small or confined aquifers in which the capacity is too low to support large irrigation or purging systems; and (iv) use in forests in which the small, low-impact droplets of the mini-sprinklers do not damage bark and in which trees can help manage (via evapotranspiration) excess waste water.
 ...
PMID:Use of mini-sprinklers to strip trichloroethylene and tetrachloroethylene from contaminated ground water. 1280 81

The ability of a multiphase flow model to capture the migration behavior of chlorinated solvents under conditions of surfactant-facilitated interfacial tension (IFT) reduction is assessed through comparison of model predictions with observations from controlled laboratory experiments. Tetrachloroethene (PCE) was released in two-dimensional saturated systems, packed with sandy media that incorporated rectangular lenses of capillary contrast. Spatially uniform interfacial tension conditions were created in the tanks by pre-flushing the porous medium with either Milli Q water or an aqueous surfactant solution. Experimental observations showed that surfactant-facilitated IFT reductions substantially lowered capillary resistance to the vertical downward migration of PCE and enabled PCE to enter finer grained, less permeable lenses that were not penetrated in the absence of surfactant. An immiscible flow model was used to simulate the conditions of the laboratory experiments. Under higher IFT conditions (47.5 and 5 dyn/cm), the model could successfully predict the general migration behavior of the organic liquid. Model predictions, however, exhibited poorer agreement with observed migration pathways under low IFT conditions (0.5 dyn/cm). In all cases, the predicted PCE distributions were influenced by selection of the parametric model for capillary retention and relative permeability. Simulated migration rates were more consistent with observed behavior when the Brooks-Corey/Burdine model was employed. For low interfacial tensions, improved predictions of migration pathways were obtained through grid refinement and incorporation of small-scale packing variability. Simulations highlight the substantial sensitivity of model predictions to the capillary pressure-scaling factor, grid resolution, and small-scale porosity variations at interfaces of permeability contrast under reduced IFT conditions.
 ...
PMID:Influence of surfactant-facilitated interfacial tension reduction on chlorinated solvent migration in porous media: observations and numerical simulation. 1281 82

Tetrachloroethene (PCE) and trichloroethene (TCE) are ideal solvents for numerous applications, and their widespread use makes them prominent groundwater pollutants. Even more troubling, natural biotic and abiotic processes acting on these solvents lead to the accumulation of toxic intermediates (such as dichloroethenes) and carcinogenic intermediates (such as vinyl chloride). Vinyl chloride was found in at least 496 of the 1,430 National Priorities List sites identified by the US Environmental Protection Agency, and its precursors PCE and TCE are present in at least 771 and 852 of these sites, respectively. Here we describe an unusual, strictly anaerobic bacterium that destroys dichloroethenes and vinyl chloride as part of its energy metabolism, generating environmentally benign products (biomass, ethene and inorganic chloride). This organism might be useful for cleaning contaminated subsurface environments and restoring drinking-water reservoirs.
 ...
PMID:Detoxification of vinyl chloride to ethene coupled to growth of an anaerobic bacterium. 1284 Jul 58

Recent studies have shown that dechlorinating bacteria can accelerate the dissolution rate of dense, nonaqueous phase liquids (DNAPLs) containing tetrachloroethene (PCE). We present an advection-dispersion-reaction model for a two-dimensional domain, with groundwater flowing over a pool of free-product PCE. PCE is converted to cis-1,2-dichloroethene (cDCE) and toxicity due to PCE or cDCE is neglected. We adopt previously published correlations relating biomass concentrations and hydraulic conductivity, accounting for biofilm growth and plug-like growth. The system of coupled equations is solved numerically. The high biotransformation rate of PCE increases the concentration gradient of PCE at the water-DNAPL interface, enhancing dissolution. The higher the electron donor (ED) concentration, the larger the dissolution enhancement. Based on the values of maximum specific rate we used, when the electron donor is unlimited, the active biomass accumulates adjacent to the water-NAPL interface and microbial reactions can significantly enhance the pool dissolution. The resulting steady-state dissolution rate can be approximated by a half-order solution when zero-order kinetics are suitable for representing the microbial reaction. However, bioclogging may significantly reduce local hydraulic conductivity; thus, it decreases the flow near the water-DNAPL interface, decreasing dissolution. When the ED is the limiting factor, active biomass accumulates away from the interface. This creates a no-flow zone between the active biomass and the interface. The enlargement of the no-flow zone, due to the donor limitation, diminishes the concentration gradient and the flushing around the water-DNAPL interface. Such adverse impacts may significantly decrease the enhancement predicted by models that do not consider the effects of bioclogging.
 ...
PMID:Effects of biomass accumulation on microbially enhanced dissolution of a PCE pool: a numerical simulation. 1285 2

The objective of this research was to determine if either methanogenic or sulfidogenic reductive dechlorination could survive an alternating anaerobic/aerobic sequence to biologically transform halogenated aliphatic hydrocarbons (HACs), specifically tetrachloroethylene (PCE), trichloroethylene (TCE), cis-1,2 dichloroethylene (cDCE), trans-1,2 dichloroethylene (tDCE), 1,1 dichloroethylene (1, 1DCE) and vinyl chloride (VC). This ability was considered to be a necessary prerequisite for complete anaerobic/aerobic mineralization of halogenated aliphatic hydrocarbons by a single microbial consortia. Chlorinated solvents, which are among the most common groundwater contaminants, have been partially dechlorinated using single-stage anaerobic environmental treatment strategies. Various types of bacteria typically reductively dechlorinate PCE and TCE to cDCE and VC in an anaerobic environment, including methanogens, sulfidogens, and homoacetogens. The problem lies in the fact that reductive dechlorination typically leads to an accumulation of daughter compounds (cDCE, VC) which are more toxic than their parent compounds (PCE, TCE). Furthermore, PCE and (to a lesser extent) TCE, are resistant to dechlorination in aerobic environments. In contrast, VC and cDCE are readily oxidized co-metabolically in an aerobic environment by methanotrophic bacteria, and others using oxygenases (e.g. toluene oxidizers). Results from this research showed that both methanogenic and sulfidogenic reductive dechlorination could resume after transient exposures to both oxygen and hydrogen peroxide (H2O2). In fact, for cycles as frequent as 10 days between aerobic treatment cycles, reductive dechlorination was observed to resume at rates at least as rapid as microcosms not exposed to aerobic treatments.
Water Sci Technol 2003
PMID:Degradation of halogenated aliphatic compounds utilizing sequential anaerobic/aerobic treatments. 1286 20

Stable carbon isotope analysis of tetrachloroethene (PCE) and trichloroethene (TCE) was applied to evaluatenatural attenuation processes in the upper Quaternary and lower Tertiary aquifer in the area of a former dry-cleaning plant located in Leipzig, Germany. Groundwater samples were taken during one monitoring campaign in 2001. The 13C enrichment in contaminants along the water flow path suggested that both, PCE and TCE were degraded in the Quaternary aquifer. The enrichment of 13C in the residual PCE fraction and an isotope fractionation factor from laboratory experiments were used to calculate the extent of biodegradation in the Quatemary aquifer. These calculations indicated that a major portion of PCE was biodegraded in the course of the plume. In the Tertiary aquifer the carbon isotope ratios of PCE and TCE indicated that the decreasing concentrations of these contaminants were probably not caused by microbial processes.
 ...
PMID:In-situ biodegradation of tetrachloroethene and trichloroethene in contaminated aquifers monitored by stable isotope fractionation. 1287 3

The industrial solvent tetrachloroethylene (PCE) is among the most ubiquitous chlorinated compounds found in groundwater contamination. The objective of this study was to evaluate the (1) feasibility of enhancing PCE biodegradation using cane molasses and sludge cakes as the primary substrates under methanogenic and iron reducing conditions, and (2) potential of installation a sludge cake/cane molasses biobarrier to clean up PCE-contaminated aquifers. The biodegradability of sludge cake (from secondary wastewater treatment system) and cane molasses was tested using bioavailability experiments. Results show that biodegradable materials were released from sludge cake/cane molasses and utilized by microbial consortia. Based on the chemical oxygen demand (COD) tests, approximately 28 and 248 mg of biodegradable COD can be released from 1g of sludge cake and 1g of cane molasses under anaerobic conditions, which have the potential to convert 70 and 620 mg of PCE to ethylene (ETH), respectively. Reductive dechlorination was evaluated using microcosms containing primary substrates (sludge cake/cane molasses) and inocula (aquifer sediments). Results indicate that sludge cake and cane molasses can serve as the diffusion sources of primary substrates, and enhance the reductive dechlorination of PCE under methanogenic processes. However, results from this study were not sufficient enough to show that reductive dechlorination of PCE would occur under iron-reducing conditions. This indicates that more studies need to be performed to further evaluate the role of iron reduction on the PCE dechlorination. Results reveal that it is feasible and applicable to install a sludge cake or cane molasses biobarrier to clean up PCE contaminated aquifers. From an engineering point of view, the sludge cake/cane molasses biobarrier has the potential to become an environmentally and economically acceptable technology for PCE bioremediation.
Water Res 2003 Dec
PMID:Enhanced PCE dechlorination by biobarrier systems under different redox conditions. 1460 34

Two-dimensional multiphase flow and transport simulators were refined and used to numerically investigate the entrapment and dissolution behavior of tetrachloroethylene (PCE) in heterogeneous porous media containing spatial variations in wettability. Measured hydraulic properties, residual saturations, and dissolution parameters were employed in these simulations. Entrapment was quantified using experimentally verified hydraulic property and residual saturation models that account for hysteresis and wettability variations. The nonequilibrium dissolution of PCE was modeled using independent estimates of the film mass transfer coefficient and interfacial area for entrapped and continuous (PCE pools or films) saturations. Flow simulations demonstrate that the spatial distribution of PCE is highly dependent on subsurface wettability characteristics that create differences in PCE retention mechanisms and the presence of subsurface capillary barriers. For a given soil texture, the maximum and minimum PCE infiltration depth was obtained when the sand had intermediate (an organic-wet mass fraction of 25%) and strong (water- or organic-wet) wettability conditions, respectively. In heterogeneous systems, subsurface wettability variations were also found to enhance or diminish the performance of soil texture-induced capillary barriers. The dissolution behavior of PCE was found to depend on the soil wettability and the spatial PCE distribution. Shorter dissolution times tended to occur when PCE was distributed over large regions due to an increased access of flowing water to the PCE. In heterogeneous systems, capillary barriers that produced high PCE saturations tended to exhibit longer dissolution times.
 ...
PMID:Entrapment and dissolution of DNAPLs in heterogeneous porous media. 1460 74

The Solvent Extraction Residual Biotreatment (SERB) technology was evaluated at a former dry cleaner site in Jacksonville, FL, where an area of tetrachloroethylene (PCE) contamination was identified. The SERB technology is a treatmenttrain approach for complete site restoration, which combines an active in situ dense nonaqueous-phase liquid (DNAPL) removal technology, cosolvent extraction, with a passive enhanced in situ bioremediation technology, reductive dechlorination. During the in situ cosolvent extraction test, approximately 34 kL of 95% ethanol/5% water (v:v) was flushed through the contaminated zone, which removed approximately 60% of the estimated PCE mass. Approximately 2.72 kL of ethanol was left in the subsurface, which provided electron donorfor enhancement of biological processes in the source zone and downgradient areas. Quarterly groundwater monitoring for over 3 yr showed decreasing concentrations of PCE in the source zone from initial values of 4-350 microM to less than 150 microM during the last sampling event. Initially there was little to no daughter product formation in the source zone, but after 3 yr, measured concentrations were 242 microM for cis-dichloroethylene (cis-DCE), 13 microM for vinyl chloride, and 0.43 microM for ethene. In conjunction with the production of dissolved methane and hydrogen and the removal of sulfate, these measurements indicate that in situ biotransformations were enhanced in areas exposed to the residual ethanol. First-order rate constants calculated from concentration data for individual wells ranged from -0.63 to -2.14 yr(-1) for PCE removal and from 0.88 to 2.39 yr(-1) for cis-DCE formation. First-order rate constants based on the change in total mass estimated from contour plots of the groundwater concentration data were 0.75 yr(-1) for cis-DCE, -0.50 yr(-1) for PCE, and -0.33 yr(-1) for ethanol. Although these attenuation rate constants include additional processes, such as sorption, dispersion, and advection, they provide an indication of the overall system dynamics. Evaluation of the groundwater data from the former dry cleaner site showed that cosolvent flushing systems can be designed and utilized to aid in the enhancement of biodegradation processes at DNAPL sites.
 ...
PMID:Field evaluation of the solvent extraction residual biotreatment technology. 1462 Aug 36

The anaerobic halorespiring microorganism, Sulfurospirillum multivorans, was observed in the pore structure of an etched silicon wafer to determine how flow hydrodynamics and mass transfer limitations along a transverse mixing zone affect biomass growth. Tetrachloroethene (PCE, an electron acceptor, 0.2 mM) and lactate (an electron donor, 2 mM) were introduced as two separate and parallel streams that mixed along a reaction line in the pore structure. The first visible biomass occupied a single line of pores in the direction of flow, a few pore bodies from the micromodel centerline. This growth was initially present as small aggregates; over time, these grew and fused to form finger-like structures with one end attached to downgradient ends of the silicon posts and the other end extending into pore bodies in the direction of flow. Biomass did not grow in pore throats as expected, presumably because shear forces were not favorable. Over the next few weeks, the line of growth migrated upward into the PCE zone and extended over a width of up to five pore spaces. When the PCE concentration was increased to 0.5 mM, the microbial biomass increased and growth migrated down toward the lactate side of the micromodel. A new analytical model was developed and used to demonstrate that transverse hydrodynamic dispersion likely caused the biomass to move in the direction observed when the PCE concentration was changed. The model was unable, however, to explain why growth migrated upward when the PCE concentration was initially constant. We postulate that this occurred because PCE, not lactate, sorbed to biofilm components and that biomass on the lactate side of the micromodel was limited in PCE. A fluorescent tracer experiment showed that biomass growth changed the water flow paths, creating a higher velocity zone in the PCE half of the micromodel. These results contribute to our understanding of biofilm growth and will help in the development of new models to describe this complex process.
 ...
PMID:Pore-scale analysis of anaerobic halorespiring bacterial growth along the transverse mixing zone of an etched silicon pore network. 1471 72


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>