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81.
Z. Ronen J.-M. Bollag 《International journal of environmental analytical chemistry》2013,93(2-4):133-143
Abstract Large amounts of aromatic compounds are produced by various industries and two thirds of these are heterocyclic chemicals. Compared with the extensive information available on microbial degradation of homocyclic aromatic compounds, relatively little is known on the transformation and biodegradation of heterocyclic chemicals in soil. Recent concerns about the persistence of hazardous pollutants have led to a renewed interest in the biodegradation of heterocyclic compounds. Hence, we investigated the microbial degradation of pyridine and some of its alkylated derivatives under aerobic and anaerobic conditions in groundwater, subsurface sediment, and soil. Results of the investigation revealed that these compounds were degraded predominantly under aerobic conditions and, to a lesser extent, under anaerobic conditions, with nitrate or sulfate serving as electron acceptors. In groundwater polluted with various pyridine derivatives, biodegradation was limited by the absence of oxygen. Therefore, we conclude that, under appropriate conditions, bioremediation is a potentially feasible method for the clean-up of environments contaminated with heterocyclic chemicals and, in particular, pyridine derivatives. 相似文献
82.
This paper presents an iterative scheme for the efficient simulation of groundwater flow in a two-dimensional, heterogeneous aquifer in which the hydraulic conductivity is anisotropic. The scheme is applicable to matrix equations arising from both mixed finite-element and cell-centered finite-difference approximations to the flow equations, and it extends readily to three space dimensions. The scheme, which generalizes an earlier technique for isotropic aquifer, admits a fast multigrid solver for hydraulic heads. Numerical experiments illustrate both the effectiveness of the scheme and the importance of accurately treating anisotropy: Small changes in the off-diagonal terms in the conductivity tensor cause relatively large changes in both the predicted heads and the Darcy velocities. 相似文献
83.
The transmissivity of a variable aperture fracture for flow of a non-Newtonian, purely viscous power-law fluid with behavior index n is studied. The natural logarithm of the fracture aperture is considered to be a two-dimensional, spatially homogeneous and correlated Gaussian random field. We derive an equivalent fracture aperture for three flow geometries: (1) flow perpendicular to aperture variation; (2) flow parallel to aperture variation; (3) flow in an isotropic aperture field. Under ergodicity, results are obtained for cases 1 and 2 by discretizing the fracture into elements of equal aperture and assuming that the resistances due to each aperture element are, respectively, in parallel and in series; for case 3, the equivalent aperture is derived as the geometric mean of cases 1 and 2. When n=1 all our expressions for the equivalent aperture reduce to those derived in the past for Newtonian flow and lognormal aperture distribution. As log-aperture variance increases, the equivalent aperture is found to increase for case 1, to decrease for case 2, and to be a function of flow behavior index n for case 3. 相似文献
84.
Quanlin Zhou Hui-Hai Liu Gudmundur S. Bodvarsson Fred J. Molz 《Transport in Porous Media》2006,63(3):473-487
Compared to values inferred from laboratory tests on matrix cores, many field tracer tests in fractured rock have shown enhanced
matrix diffusion coefficient values (obtained using a single-process matrix-diffusion model with a homogeneous matrix diffusion
coefficient). To investigate this phenomenon, a conceptual model of multi-process matrix diffusion in a single-fracture system
was developed. In this model, three matrix diffusion processes of different diffusion rates were assumed to coexist: (1) diffusion
into stagnant water and infilling materials within fractures, (2) diffusion into a degraded matrix zone, and (3) further diffusion
into an intact matrix zone. The validity of the conceptual model was then demonstrated by analyzing a unique tracer test conducted
using a long-time constant-concentration injection. The tracer-test analysis was conducted using a numerical model capable
of tracking the multiple matrix-diffusion processes. The analysis showed that in the degraded zone, a diffusion process with
an enhanced diffusion rate controlled the steep rising limb and decay-like falling limb in the observed breakthrough curve,
whereas in the intact matrix zone, a process involving a lower diffusion rate affected the long-term middle platform of slowly
increasing tracer concentration. The different matrix-diffusion-coefficient values revealed from the field tracer test are
consistent with the variability of matrix diffusion coefficient measured for rock cores with different degrees of fracture
coating at the same site. By comparing to the matrix diffusion coefficient calibrated using single-process matrix diffusion,
we demonstrated that this multi-process matrix diffusion may contribute to the enhanced matrix-diffusion-coefficient values
for single-fracture systems at the field scale. 相似文献
85.
Application of Boundary-Fitted Coordinate Transformations to groundwater flow modeling 总被引:4,自引:0,他引:4
The Boundary-Fitted Coordinate (BFC) Transformation method is a very powerful, efficient and accurate method of modeling heat or fluid flow in two- or three-dimensional domains with complex boundary shapes and abrupt changes in internal properties. Since the late 1970's it has become the modeling method of choice among many aerodynamicists and heat-flow modelers. It is being presented here for the first time as a new approach to modeling groundwater flow, based on successful research results in two dimensions. The BFC transformation method was employed to simulate two hypothetical well-flow scenarios in isotropic and anisotropic domains, and actual groundwater flows in the area of West Lafayette, Indiana. The numerical solutions in those cases were at least as accurate as and/or consistent with those obtained by purely finite difference and finite element methods, but with the added advantage of more accurate representation and implementation of the boundary condition in the region of great sensitivity. The BFC method successfully applied to two-dimensional simulations should be easily extended to simulations of three-dimensional flow and transport and thus, this research is continuing in that direction. 相似文献
86.
Hsueh-Yu Lu 《Isotopes in environmental and health studies》2014,50(1):18-32
In this paper, hydrochemistry and boron isotopes are successfully applied to elucidate hydrogeological processes by the use of natural tracers. The hydrochemical analysis identifies four end-members in the hydrochemical evolution of groundwater from the North Chianan plain groundwater district. A few groundwater contain extraordinary chlorine concentrations of up to 48,000 mg l?1. However, the hydrochemistry of groundwater only reveals that high saline water is a dominant factor in groundwater hydrochemistry. It is thought that these groundwater experienced precipitation of carbonates during seawater evaporation that did not involve the precipitation of gypsum. Boron isotopes are very efficient tracers in determining the source of salinisation. The boron isotopes reveal the results of mixing of evaporated seawater and water–sediment interaction. In general, the boron isotope ratio of the groundwater is controlled by a two-end-member mixing system, which is composed of evaporated seawater (isotopically heavy) and fresh surface water (isotopically light). Due to a long lagoonal period in the coastal plain, the groundwaters in the downstream area generally have high Cl/B ratios and relatively heavy boron isotope ratios while those in the upstream area are composed of low Cl/B and light boron isotopes. However, there is not a resolvable mixing trend between the Cl/B ratio and the isotopic composition of boron. It is probably obscured by a highly variable boron isotope ratio in fresh surface water and through fractionation associated with water–rock interaction. Both factors would decrease the boron isotope ratio but one effect cannot be distinguished from the other. 相似文献
87.
Alexandra Gemitzi Kyriakos Stefanopoulos Marie Schmidt Hans H. Richnow 《Isotopes in environmental and health studies》2014,50(1):74-87
The present study investigates the complex interactions among surface waters, groundwaters and a coastal lake in northeastern Greece, using their stable isotopic composition (δ18O, δ2H) in combination with hydrogeological and hydrochemical data. Seasonal and spatial trends of water isotopes were studied and revealed that all water bodies in the study area interact. It was also shown that the aquifer's increased salinity is not due to fossil water from past geological periods, but is attributed to brackish lake water intrusion into the aquifer induced by the extensive groundwater pumping for irrigation purposes. Quantification of the contribution of the lake to the aquifer was achieved using the simple dilution formula. The isotopic signatures of the seawater and the groundwaters are considerably different, so there is a very little possibility of direct seawater intrusion into the aquifer. 相似文献
88.
Yin‐shan Yun Temuer Chaolu Jun‐sheng Duan 《Mathematical Methods in the Applied Sciences》2014,37(16):2406-2418
Based on Adomian decomposition method, a new algorithm for solving boundary value problem (BVP) of nonlinear partial differential equations on the rectangular area is proposed. The solutions obtained by the method precisely satisfy all boundary conditions, except the small pieces near the four corners of the rectangular area. A theorem on the boundary error is given. Hence, the Adomian decomposition method is more efficiently applied to BVPs for partial differential equations. Segmented and weighted analytical solutions with a high accuracy for the BVP of nonlinear groundwater equations on a rectangular area are obtained by the present algorithm. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
89.
R. Heyer H.-J. Stan 《International journal of environmental analytical chemistry》2013,93(1-4):173-183
Abstract The aim of the investigation was to evaluate whether the results of field studies and those obtained from soil column experiments are comparable in order to describe leaching behaviour of pesticides. The fate of Alachlor and its metabolites 2,6-diethylaniline and 2-chloro-2′,6′-diethylacetanilide are described in this paper. Field leaching study and laboratory soil column experiments carried out with the formulated herbicide LASSO gave similar results. Applied Alachlor remained mostly in the top 10cm soil layer representing a limited mobility. Very small amounts of Alachlor in ground and percolated water indicated only a slight leaching potential. The calculated half-life of 15 days and 90% loss after 335 days demonstrate a remarkable persistence of alachlor. Only 2-chloro-2′,6′-diethylacetanilide but not 2,6-diethylaniline was detected in soil and percolated water. It is still uncertain if these residues originate from the formulated product or result partially from “metabolism”. Column experiments with the same soil carried out under undisturbed conditions are a simple alternative to field studies and allow quantitative estimations. The column experiments support the assumption that most of the alachlor that cannot be found after application is not lost by wind drifting or volatilization but due to formation of bound residues. 相似文献
90.
We studied transboundary groundwater management problems in the presence of hydraulic fracturing. We found that the presence of risk suggests there should be caution when considering hydraulic fracturing. Our results from the cooperative solution show a decrease in hydraulic fracturing and increase in the steady state survival rate of groundwater. We also provide a Pigouvian type tax that could be imposed on natural gas developers. 相似文献