共查询到20条相似文献,搜索用时 15 毫秒
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F. A. Lopes G. Michard M. Poulin A. Roué F. Prévot D. Jézéquel E. Viollier 《Aquatic Geochemistry》2010,16(4):587-610
A reactive transport model was developed to describe seasonal variations of biogeochemical and physical processes in Lake
Aydat. The model includes physical processes such as vertical mixing, sedimentation and advection related to inflows into
the lake and biogeochemical conversion processes in the water column and in the sediment surface layer. The reactions described
in the model include primary redox reactions such as primary production, aerobic and anaerobic respiration, methanogenesis
and secondary reactions established between oxidants and reducers produced by the primary reactions. After adjusting various
kinetic constants, the model reasonably reproduced the main features of seasonal variations of dissolved oxygen and nitrate
depth profiles and pH. The reactive transport model was also used to quantify the relative importance of different biogeochemical
pathways. For instance, ferrous denitrification seems to play an important role when stratification is increasing. 相似文献
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《Applied Geochemistry》2000,15(1):35-49
A comparative assessment of two reactive-transport models, PHREEQC and HYDROGEOCHEM (HGC), was done to determine the suitability of each for simulating the movement of acidic contamination in alluvium. For simulations that accounted for aqueous complexation, precipitation and dissolution, the breakthrough and rinseout curves generated by each model were similar. The differences in simulated equilibrium concentrations between models were minor and were related to (1) different units in model output, (2) different activity coefficients, and (3) ionic-strength calculations. When adsorption processes were added to the models, the rinseout pH simulated by PHREEQC using the diffuse double-layer adsorption model rose to a pH of 6 after pore volume 15, about 1 pore volume later than the pH simulated by HGC using the constant-capacitance model.In PHREEQC simulation of a laboratory column experiment, the inability of the model to match measured outflow concentrations of selected constituents was related to the evident lack of local geochemical equilibrium in the column. The difference in timing and size of measured and simulated breakthrough of selected constituents indicated that the redox and adsorption reactions in the column occurred slowly when compared with the modeled reactions. MINTEQA2 and PHREEQC simulations of the column experiment indicated that the number of surface sites that took part in adsorption reactions was less than that estimated from the measured concentration of Fe hydroxide in the alluvium. 相似文献
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Reactive Transport Modeling of Subaqueous Sediment Caps and Implications for the Long-Term Fate of Arsenic, Mercury, and Methylmercury 总被引:1,自引:0,他引:1
Brad A. Bessinger Dimitri Vlassopoulos Susana Serrano Peggy A. O’Day 《Aquatic Geochemistry》2012,18(4):297-326
A 1-D biogeochemical reactive transport model with a full set of equilibrium and kinetic biogeochemical reactions was developed to simulate the fate and transport of arsenic and mercury in subaqueous sediment caps. Model simulations (50?years) were performed for freshwater and estuarine scenarios with an anaerobic porewater and either a diffusion-only or a diffusion plus 0.1-m/year upward advective flux through the cap. A biological habitat layer in the top 0.15?m of the cap was simulated with the addition of organic carbon. For arsenic, the generation of sulfate-reducing conditions limits the formation of iron oxide phases available for adsorption. As a result, subaqueous sediment caps may be relatively ineffective for mitigating contaminant arsenic migration when influent concentrations are high and sorption capacity is insufficient. For mercury, sulfate reduction promotes the precipitation of metacinnabar (HgS) below the habitat layer, and associated fluxes across the sediment–water interface are low. As such, cap thickness is a key design parameter that can be adjusted to control the depth below the sediment–water interface at which mercury sulfide precipitates. The highest dissolved methylmercury concentrations occur in the habitat layer in estuarine environments under conditions of advecting porewater, but the highest sediment concentrations are predicted to occur in freshwater environments due to sorption on sediment organic matter. Site-specific reactive transport simulations are a powerful tool for identifying the major controls on sediment- and porewater-contaminant arsenic and mercury concentrations that result from coupling between physical conditions and biologically mediated chemical reactions. 相似文献
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This paper deals with a field experiment, combining the push–pull and tracer tests, conducted under natural gradient conditions
at the international Oslo airport. The studied aquifer, showing very complex hydrogeological settings, has been contaminated
by a jet fuel spill. The tracer solutes—bromide, toluene, o-xylene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene and naphthalene, have been injected into the plume. Their migration
and changes in concentration of the electron acceptors and metabolic by-products have been monitored. Fast removal of both
the non-reactive tracer as well as the aromatic organics has been observed. The tracer pulse could only be detected 2 m downgradient
from the injection points. At this point, toluene and o-xylene have been completely removed, however, trimethylbenzenes and naphthalene have been detected. Their depletion, based
on calculations of available electron acceptors, can, to a large extent, be accounted for intrinsic biodegradation, with Fe(III)
and sulphate reductions as the major controlling processes. 相似文献
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《Applied Geochemistry》1998,13(2):257-268
We report the hydrogeochemical modeling of a complicated suite of reactions that take place during the oxidation of pyrite in a marine sediment. The sediment was equilibrated in a column with MgCl2 solution and subsequently oxidized with H2O2. The oxidation of pyrite triggers dissolution of calcite, cation and proton exchange, and CO2 sorption. The composition of the column effluent was modeled with PHREEQC, a hydrogeochemical transport model. The model was extended with a formal ID transport module which includes dispersion and diffusion. The algorithm solves the advection-reaction-dispersion equation with explicit finite differences in a split-operator scheme. Also, kinetic reactions for pyrite oxidation, calcite dissolution and precipitation, and organic C oxidation were included. Kinetic relations for pyrite oxidation and calcite dissolution were taken from the literature, and a coefficient equivalent to the ratio A/V (surface over volume), was adjusted to fit the experimental data. The comparison of model and experiment shows that ion exchange and sorption are dominant chemical processes in regulating and buffering water quality changes upon the oxidation of pyrite. Cation exchange was assigned to the colloidal fraction ( < 2 μm) and deprotonated organic matter, proton buffering to organic matter, and CO2 sorption to amorphous Fe-oxyhydroxide. These processes have been neglected in earlier modeling studies of pyrite oxidation in natural sediments. 相似文献
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Hywel Rhys Thomas Majid Sedighi Philip James Vardon 《Geotechnical and Geological Engineering》2012,30(4):841-857
This paper presents an investigation of the reactive transport of multicomponent chemicals in clays under coupled thermal, hydraulic, chemical and mechanical framework, considering the diffusion processes in detail. More specifically, combined effects due to the electrochemical and the thermal diffusion potentials are investigated. A theoretical framework for coupling thermal diffusion, i.e. the Soret effect, with electrochemical diffusion in a multi-ionic system is provided. An explicit form of a definition for the thermal diffusion coefficient in a multicomponent chemical transport model is developed. Chemical transport is linked to an advanced geochemical model, PHREEQC (version 2), in order to include chemical reactions. The effects of the combined diffusion potentials on the reactive transport of multicomponent chemicals are investigated by a series of numerical simulations of coupled thermal, hydraulic and chemical behaviour. 相似文献
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S. Sevin engr Nicolas F. Spycher Timothy R. Ginn Rajesh K. Sani Brent Peyton 《Applied Geochemistry》2007,22(12):2569-2594
Decades of runoff from precious-metal mining operations in the Lake Coeur d’Alene Basin, Idaho, have left the sediments in this lake heavily enriched with toxic metals, most notably Zn, Pb and Cu, together with As. The bioavailability, fate and transport of these metals in the sediments are governed by complex biogeochemical processes. In particular, indigenous microbes are capable of catalyzing reactions that detoxify their environments, and thus constitute an important driving component in the biogeochemical cycling of these metals. Here, the development of a quantitative model to evaluate the transport and fate of Zn, Pb and Cu in Lake Coeur d’Alene sediments is reported. The current focus is on the investigation and understanding of local-scale processes, rather than the larger-scale dynamics of sedimentation and diagenesis, with particular emphasis on metal transport through reductive dissolution of Fe hydroxides. The model includes 1-D inorganic diffusive transport coupled to a biotic reaction network including consortium biodegradation kinetics with multiple terminal electron acceptors and syntrophic consortium biotransformation dynamics of redox front. The model captures the mobilization of metals initially sorbed onto hydrous ferric oxides, through bacterial reduction of Fe(III) near the top of the sediment column, coupled with the precipitation of metal sulfides at depth due to biogenic sulfide production. Key chemical reactions involve the dissolution of ferrihydrite and precipitation of siderite and Fe sulfide. The relative rates of these reactions play an important role in the evolution of the sediment pore-water chemistry, notably pH, and directly depend on the relative activity of Fe and SO4 reducers. The model captures fairly well the observed trends of increased alkalinity, sulfide, Fe and heavy metal concentrations below the sediment–water interface, together with decreasing terminal electron acceptor concentrations with depth, including the development of anoxic conditions within about a centimeter below the lake bottom. This effort provides insights on important biogeochemical processes affecting the cycling of metals in Lake Coeur d’Alene and similar metal-impacted lacustrine environments. 相似文献
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PHREEQC在地下水溶质反应-运移模拟中的应用 总被引:7,自引:2,他引:7
由于地下水污染的加剧,对地下水中污染物运移规律的研究日益受到重视。地下水中的溶质在运移过程中伴随着溶质组分间的化学反应,因此需要建立地下水溶质运移与化学反应的耦合模型。PHREEQC是近年来发展起来的描述局部平衡反应、动态生物化学反应的水文地球化学模拟软件。本文利用该模拟软件对一维地下水流动过程中溶质离子交换反应和动态氧化还原反应进行了模拟。结果表明,PHREEQC能够成功地进行溶质运移情况下复杂水化学反应模拟,但对于复杂地下水流和溶质运动的情况,有必要耦合其它的地下水流动和溶质运移软件来共同完成。 相似文献
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A non‐equilibrium sorption—advection—diffusion model to simulate miscible pollutant transport in saturated–unsaturated soils is presented. The governing phenomena modelled in the present simulation are: convection, molecular diffusion, mechanical dispersion, sorption, immobile water effect and degradation, including both physical and chemical non‐equilibrium processes. A finite element procedure, based on the characteristic Galerkin method with an implicit algorithm is developed to numerically solve the model equations. The implicit algorithm is formulated by means of a combination of both the precise and the traditional numerical integration procedures. The stability analysis of the algorithm shows that the unconditional stability of the present implicit algorithm is enhanced as compared with that of the traditional implicit numerical integration procedure. The numerical results illustrate good performance of the present algorithm in stability and accuracy, and in simulating the effects of all the mentioned phenomena governing the contaminant transport and the concentration distribution. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
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Rémi Marsac Mélanie Davranche Gérard Gruau Martine Bouhnik-Le Coz Aline Dia 《Geochimica et cosmochimica acta》2011,75(19):5625-5637
The Humic Ion Binding Model VI (Model VI) - previously used to model the equilibrium binding of rare earth elements (REE) by humic acid (HA) - was modified to account for differences in the REE constant patterns of the HA carboxylic and phenolic groups, and introduced into PHREEQC to calculate the REE speciation on the HA binding sites. The modifications were shown to greatly improve the modeling. They allow for the first time to both satisfactorily and simultaneously model a large set of multi-REE experimental data with the same set of equations and parameters. The use of PHREEQC shows that the light rare earth elements (LREE) and heavy rare earth elements (HREE) do not bind to HA by the same functional groups. The LREE are preferentially bound to carboxylic groups, whereas the HREE are preferentially bound to carboxy-phenolic and phenolic groups. This binding differentiation might lead to a fractionation of REE-HA patterns when competition between REE and other metals occur during complexation. A survey of the available data shows that competition with Al3+ could lead to the development of HREE-depleted HA patterns. This new model should improve the hydrochemical modeling of the REE since PHREEQC takes into account chemical reactions such as mineral dissolution/precipitation equilibrium and redox reactions, but also models kinetically controlled reactions and one-dimensional transport. 相似文献
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William D. Burgos Yilin Fang Gour-Tsyh Yeh Byong-Hun Jeon 《Geochimica et cosmochimica acta》2003,67(15):2735-2748
This paper presents and validates a new paradigm for modeling complex biogeochemical systems using a diagonalized reaction-based approach. The bioreduction kinetics of hematite (α-Fe2O3) by the dissimilatory metal-reducing bacterium (DMRB) Shewanella putrefaciens strain CN32 in the presence of the soluble electron shuttling compound anthraquinone-2,6-disulfonate (AQDS) is used for presentation/validation purposes. Experiments were conducted under nongrowth conditions with H2 as the electron donor. In the presence of AQDS, both direct biological reduction and indirect chemical reduction of hematite by bioreduced anthrahydroquinone-2,6-disulfonate (AH2DS) can produce Fe(II). Separate experiments were performed to describe the bioreduction of hematite, bioreduction of AQDS, chemical reduction of hematite by AH2DS, Fe(II) sorption to hematite, and Fe(II) biosorption to DMRB. The independently determined rate parameters and equilibrium constants were then used to simulate the parallel kinetic reactions of Fe(II) production in the hematite-with-AQDS experiments. Previously determined rate formulations/parameters for the bioreduction of hematite and Fe(II) sorption to hematite were systematically tested by conducting experiments with different initial conditions. As a result, the rate formulation/parameter for hematite bioreduction was not modified, but the rate parameters for Fe(II) sorption to hematite were modified slightly. The hematite bioreduction rate formulation was first-order with respect to hematite ”free“ surface sites and zero-order with respect to DMRB based on experiments conducted with variable concentrations of hematite and DMRB. The AQDS bioreduction rate formulation was first-order with respect to AQDS and first-order with respect to DMRB based on experiments conducted with variable concentrations of AQDS and DMRB. The chemical reduction of hematite by AH2DS was fast and considered to be an equilibrium reaction. The simulations of hematite-with-AQDS experiments were very sensitive to the equilibrium constant for the hematite-AH2DS reaction. The model simulated the hematite-with-AQDS experiments well if it was assumed that the ferric oxide “surface” phase was more disordered than pure hematite. This is the first reported study where a diagonalized reaction-based model was used to simulate parallel kinetic reactions based on rate formulations/parameters independently obtained from segregated experiments. 相似文献
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Y. A. Londoño G. A. Peñuela 《International Journal of Environmental Science and Technology》2018,15(9):1887-1896
This study evaluated three types of pharmaceuticals and personal care products (methylparaben, ibuprofen and triclosan) at concentration levels of 300, 500, 1000 and 2000 µg/L by implementing batch tests using anaerobic processes and granular biomass. The study aimed to identify the mechanisms of biodegradation and sorption in the degradation of these compounds. The inoculum was granular sludge from a laboratory-scale anaerobic reactor. The characterization results of the inoculum showed an anaerobic biomass with high activity, good sedimentation and a high percentage of organic matter. The results of the removal of the pollutants showed high degradation percentages for methylparaben (close to 99%), with negligible sorption in the sludge. The results also showed insignificant ibuprofen sorption but removal close to 0%. Triclosan showed high biomass sorption and low biodegradation. In addition, at the concentrations tested, none of the compounds had a negative or inhibitory effect on the microbial populations of the system. 相似文献
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Interaction of various physical, chemical and biological transport processes plays an important role in deciding the fate and migration of contaminants in groundwater systems. In this study, a numerical investigation on the interaction of various transport processes of BTEX in a saturated groundwater system is carried out. In addition, the multi-component dissolution from a residual BTEX source under unsteady flow conditions is incorporated in the modeling framework. The model considers Benzene, Toluene, Ethyl Benzene and Xylene dissolving from the residual BTEX source zone to undergo sorption and aerobic biodegradation within the groundwater aquifer. Spatial concentration profiles of dissolved BTEX components under the interaction of various sorption and biodegradation conditions have been studied. Subsequently, a spatial moment analysis is carried out to analyze the effect of interaction of various transport processes on the total dissolved mass and the mobility of dissolved BTEX components. Results from the present numerical study suggest that the interaction of dissolution, sorption and biodegradation significantly influence the spatial distribution of dissolved BTEX components within the saturated groundwater system. Mobility of dissolved BTEX components is also found to be affected by the interaction of these transport processes. 相似文献
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Trimethylbenzene (TMB), as a constituent of gasoline, is often expected to be used as a conservative tracer in anaerobic BTEX-contaminated
groundwater site to correct for attenuation due to dispersion, dilution and sorption along a flow path. To evaluate the suitability
of using TMB as a tracer and to better understand biodegradability of TMB in contaminated groundwater by gasoline under anaerobic
conditions, laboratory microcosms were conducted with mixed nitrate/iron/sulfate electron-acceptor amendments, using aquifer
materials collected from Canadian Forces Base (CFB), Borden, Ontario, Canada. The results showed that under denitrifying conditions,
biodegradation of 1,3,5-TMB, 1,2,4-TMB and 1,2,3-TMB were relatively slow and after 204 days of incubation approximately 27,
24, and 16% of the initial concentrations, respectively, were degraded in the microcosms. Under sulfate-reducing conditions,
TMB isomers were recalcitrant. In contrast, significant biodegradation of TMB was observed under iron-reducing conditions.
1,3,5-TMB, 1,2,4-TMB and 1,2,3-TMB were degraded to 44, 47, and 24% of initial concentrations with first-order biodegradation
rate constants of 0.003, 0.006 and 0.013 d−1, respectively. This study indicates that TMB biodegradation is insignificant under nitrate and sulfate-reducing conditions
but significant under iron-reducing conditions. Therefore, the use of TMB as a tracer for interpreting removal of other biodegradable
gasoline constituents such as BTEX requires caution, especially in the presence of iron-reducing conditions. 相似文献
17.
Surface reaction versus diffusion control of mineral dissolution and growth rates in geochemical processes 总被引:2,自引:0,他引:2
The kinetics of chemical reactions at mineral surfaces and the rates of diffusion of species in an aqueous phase are coupled in many geochemical systems. Analytical solutions to equations describing coupled mineral dissolution/growth and solute transport in both transient and steady-state systems are used to delimit regimes of pure reaction control, pure transport control and mixed kinetic control of mass-transfer rates. The relative significance of the two processes depends on the magnitudes of the diffusion coefficients and rate constants as functions of temperature, and the degree of disequilibrium in the system. In addition, the system geometry, the ratio of mineral surface area to diffusion cross-section, and the porosity and tortuosity of the medium through which aqueous species diffuse affect reaction vs. diffusion control. In general, diffusion control increases with increasing temperature and increasing distance over which diffusion occurs. Calculations for the mixed kinetic regime in transient systems demonstrate that the relative significance of diffusion and surface reaction varies with reaction progress, and approaches a limiting value as equilibrium is approached. This limiting value may be appropriate to natural water-rock interactions that occur at conditions that are close to equilibrium. This result permits extension of simple models for irreversible mass transfer in homogeneous systems to systems in which mass-transfer kinetics are controlled by coupled surface reactions and mass transport. Criteria are established for time and length scales and fluid velocity limits on the validity of the continuum hypothesis and the local equilibrium assumption in mass-transport modeling. 相似文献
18.
Intrinsic biodegradation of toluene coupled with the microbial reduction of ferric iron (Fe(III)) as the terminal electron acceptor was studied by using laboratory column experiments under continuous flow conditions. Columns were packed with contaminated aquifer sediment and N2-purged groundwater taken from the western part of the Gardermoen aquifer. The columns were operated anaerobically at 8 °C (in-situ temperature). Chloride was initially used to characterize flow properties of the columns. Intrinsic biodegradation of toluene, including abiotic loss and biological loss, was estimated by comparing breakthrough curves of toluene for live columns and sterilized control columns based on mass balance in steady-state conditions. The column experiments were run at two different flow velocities. The estimated average intrinsic rate was -0.73 and -0.53 mM day-1 for pore-water velocities of 1.75 and 2.68 cm h-1, respectively, corresponding to -0.27 and -0.22 mM day-1 in biological loss rate. The results indicate that intrinsic biodegradation of toluene could be used as an efficient remediation approach for contaminated groundwater at the Gardermoen fire-fighting training site. 相似文献
19.
Geochemical reactive transport modeling was coupled to bench-scale leaching experiments to investigate and verify the mobilization of geogenic arsenic (As) under a range of redox conditions from an arsenic-rich pyrite bearing limestone aquifer. Modeling and experimental observations showed similar results and confirmed the following: (1) native groundwater and aquifer matrix, including pyrite, were in chemical equilibrium, thus preventing the release of As due to pyrite dissolution under ambient conditions; (2) mixing of oxygen- and nitrate-rich surface water with oxygen-depleted native groundwater changed the redox conditions and promoted the dissolution of pyrite, and (3) the behavior of As along a flow path was controlled by a complex series of interconnected reactions. This included the oxidative dissolution of pyrite and simultaneous sorption of As onto neo-formed hydrous ferric oxides (HFO), followed by the reductive dissolution of HFO and secondary release of adsorbed As under reducing conditions. Arsenic contamination of drinking water in these systems is thus controlled by the re-equilibration of the system to more reducing conditions rather than a purely oxidative process. 相似文献
20.
Konrad Miotliński 《Aquatic Geochemistry》2008,14(2):117-131
The reactive transport modeling of a complicated suite of reactions apparent in the aquifer during the application of N-containing
fertilizers is reported. The unconfined sandy aquifer can be subdivided into an oxic zone which contains groundwater with
oxygen and nitrate and an anoxic zone characterized by elevated iron and sulfate concentrations in groundwater. Oxygen and
nitrate are being reduced by pyrite and organic matter that commonly apparent in the aquifer. The oxidation of pyrite is modeled
using the local equilibrium approach, whereas decomposition of organic matter, with the adoption of kinetic approach. The
system is buffered by dissolution of aluminum and iron oxides. The modeling process is a two-step procedure. First, the processes
are modeled in the one-dimensional (1D) column using PHREEQC code. Subsequently, the calibrated and verified data were copied
and used in two-dimensional (2D) PHAST model. Prior to the performance of reactive transport modeling operations with PHAST,
a reliable flow model was executed. Finally, predictions are made for the distribution of water chemistry for the year 2008.
Model predicts that sulfate derived from the ongoing pyrite oxidation is reduced by the dissolved organic carbon at the higher
depth and forms pyrite by the reaction with iron. The results of this study highlight the importance of understanding the
interplay between the transport and chemical reactions that occur during the input of nitrate to the aquifer. Reactive transport
modeling incorporating the use of a newly developed code PHAST have proved to be a powerful tool for analyzing and quantifying
such interactions. 相似文献