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Journal ArticleDOI

Numerical modelling on fate and transport of coupled adsorption and biodegradation of pesticides in an unsaturated porous medium

29 Mar 2016-ISH Journal of Hydraulic Engineering (Taylor & Francis)-Vol. 22, Iss: 3, pp 236-246
TL;DR: In this article, a one-dimensional numerical model is developed to simulate the transport of pesticides in an unsaturated porous medium, considering the effect of adsorption and microbial degradation with inhibition in addition to conventional advective and dispersive transport.
Abstract: The vertical transport of pesticides from a surface application through an unsaturated porous medium system is of major concern to assess the vulnerability of groundwater contamination. In order to better understand the transport of pesticides in the groundwater, it is essential to understand the flow and predict the pesticide concentration in the unsaturated zone. A one-dimensional numerical model is developed to simulate the transport of pesticides in an unsaturated porous medium, considering the effect of adsorption and microbial degradation with inhibition in addition to conventional advective and dispersive transport. The effect of unsaturated soil parameters on the water flow dynamics and the factors governing the pesticide transport in an unsaturated porous medium is also numerically investigated. The numerical results suggest that the adsorption and biodegradation is an important sink in contaminant removal. In addition, the microbial growth inhibition due to pesticide restricts the potent...
Citations
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Journal ArticleDOI
10 Jun 2020
TL;DR: In this article, the authors focus on the constraints associated with the extended version of Darcy's law that is used to describe the multiphase flow through a porous media; and in particular, a petroleum reservoir.
Abstract: This manuscript primarily focuses on the constraints associated with the extended version of Darcy’s law that is used to describe the multiphase flow through a porous media; and in particular, a petroleum reservoir. This manuscript clearly brings out the basics associated with the usage of Darcy’s law, and reasons out the inapplicability of the Navier-Stokes Equation in order to describe the momentum conservation in a typical petroleum reservoir. Further, this work highlights the essence of continuum-based Darcy’s macroscopic-scale equation with that of Navier-Stokes’s microscopic-scale equation. Further, the absence of capillary forces in original Darcy’s equation and extending the same by considering the concept of ‘capillary pressure’ in order to accommodate the multi-phase flow has several critical constraints associated with it. In this manuscript, all these constraints or limitations have been posed in the form of a list of basic queries that need to be addressed or at least to be understood with clarity, when applying the multi-phase fluid flow equations associated with a petroleum reservoir. This study is limited to an oil-water two-phase system.

1 citations


Additional excerpts

  • ...…Vivek and Kumar, 2020; Mohanasundaram et al., 2013a, 2013b; Berlin et al., 2013; Berlin et al., 2014a, 2014b; Berlin et al., 2015a, 2015b, 2015c; Omkar et al., 2016a, 2016b; Mohanasundaram et al., 2017; Berlin et al., 2018a, 2018b; Omkar et al., 2019a, 2019b; Berlin and Kumar, 2019;…...

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Journal ArticleDOI
TL;DR: In this paper , a state-of-the-art synthesis of research on soil and groundwater contamination by crude oil is presented, including processes, measurements, predictions, and management, as well as an analysis of the state and challenges in Nigeria.
Abstract: Management of soil and groundwater resources has been recognized as essential to meeting the sustainable development goals of Agenda 2063 of the African Union. As Africa’s fastest growing population with over 200 million people, Nigeria is responsible for leading the continent’s environmental sustainability goal. Nigeria has seen a sizable number of crude oil spillages that have contaminated its soils and groundwater resources, and several of these contaminated sites are to be cleaned up yet. There needs to be more scientific data to design an effective cleanup and to manage the soil and groundwater resources effectively. So far, the only extensive crude oil-contaminated site remediation project documented is on Ogoniland in the Niger Delta region of Nigeria. However, this project resulted in less effective, albeit temporary, cleanup solutions. This review presents a state-of-the-art synthesis of research on soil and groundwater contamination by crude oil. It includes sections on processes, measurements, predictions, and management, as well as an analysis of the state and challenges in Nigeria. In-depth field, laboratory, and computer models for crude oil contamination investigation have been developed with over 60 years of significant research. However, studies and case projects in Nigeria have relied on point sampling to determine the concentration of crude oil contaminants in soil and groundwater. This method offers limited information on the solute concentration and hydraulic distribution, which regulates pollutant mobility within the subsurface. The absence of baseline and high-resolution subsurface characterization data has also resulted in a need for more process-based knowledge to direct the development of site-specific remediation strategies. As a result, it is challenging to design a conceptual model that is detailed enough to help with predictions of the flow dynamics of crude oil contaminants in the unsaturated and saturated zones. It is anticipated that this review will stimulate further multidisciplinary research through site evaluation and monitoring to provide reliable information that can be used to develop appropriate model-based remediation solutions.
References
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Journal ArticleDOI
TL;DR: Van Genuchten et al. as mentioned in this paper proposed a closed-form analytical expression for predicting the hydraulic conductivity of unsaturated soils based on the Mualem theory, which can be used to predict the unsaturated hydraulic flow and mass transport in unsaturated zone.
Abstract: A new and relatively simple equation for the soil-water content-pressure head curve, 8(h), is described in this paper. The particular form of the equation enables one to derive closedform analytical expressions for the relative hydraulic conductivity, Kr, when substituted in the predictive conductivity models of N.T. Burdine or Y. Mualem. The resulting expressions for Kr(h) contain three independent parameters which may be obtained by fitting the proposed soil-water retention model to experimental data. Results obtained with the closed-form analytical expressions based on the Mualem theory are compared with observed hydraulic conductivity data for five soils with a wide range of hydraulic properties. The unsaturated hydraulic conductivity is predicted well in four out of five cases. It is found that a reasonable description of the soil-water retention curve at low water contents is important for an accurate prediction of the unsaturated hydraulic conductivity. Additional Index Words: soil-water diffusivity, soil-water retention curve. van Genuchten, M. Th. 1980. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Sci. Soc. Am. J. 44:892-898. T USE OF NUMERICAL MODELS for simulating fluid flow and mass transport in the unsaturated zone has become increasingly popular the last few years. Recent literature indeed demonstrates that much effort is put into the development of such models (Reeves and Duguid, 1975; Segol, 1976; Vauclin et al., 1979). Unfortunately, it appears that the ability to fully characterize the simulated system has not kept pace with the numerical and modeling expertise. Probably the single most important factor limiting the successful application of unsaturated flow theory to actual field problems is the lack of information regarding the parameters entering the governing transfer equations. Reliable estimates of the unsaturated hydraulic conductivity are especially difficult to obtain, partly because of its extensive variability in the field, and partly because measuring this parameter is time-consuming and expensive. Several investigators have, for these reasons, used models for calculating the unsaturated conductivity from the more easily measured soil-water retention curve. Very popular among these models has been the Millington-Quirk method (Millington and Quirk, 1961), various forms of which have been applied with some success in a number of studies (cf. Jackson et al., 1965; Jackson, 1972; Green and Corey, 1971; Bruce, 1972). Unfortunately, this method has the disadvantage of producing tabular results which, for example when applied to nonhomogeneous soils in multidimensional unsaturated flow models, are quite tedious to use. Closed-form analytical expressions for predicting 1 Contribution from the U. S. Salinity Laboratory, AR-SEA, USDA, Riverside, CA 92501. Received 29 June 1979. Approved 19 May I960. 'Soil Scientist, Dep. of Soil and Environmental Sciences, University of California, Riverside, CA 92521. The author is located at the U. S. Salinity Lab., 4500 Glenwood Dr., Riverside, CA 92502. the unsaturated hydraulic conductivity have also been developed. For example, Brooks and Corey (1964) and Jeppson (1974) each used an analytical expression for the conductivity based on the Burdine theory (Burdine, 1953). Brooks and Corey (1964, 1966) obtained fairly accurate predictions with their equations, even though a discontinuity is present in the slope of both the soil-water retention curve and the unsaturated hydraulic conductivity curve at some negative value of the pressure head (this point is often referred to as the bubbling pressure). Such a discontinuity sometimes prevents rapid convergence in numerical saturated-unsaturated flow problems. It also appears that predictions based on the Brooks and Corey equations are somewhat less accurate than those obtained with various forms of the (modified) Millington-Quirk method. Recently Mualem (1976a) derived a new model for predicting the hydraulic conductivity from knowledge of the soil-water retention curve and the conductivity at saturation. Mualem's derivation leads to a simple integral formula for the unsaturated hydraulic conductivity which enables one to derive closed-form analytical expressions, provided suitable equations for the soil-water retention curves are available. It is the purpose of this paper to derive such expressions using an equation for the soil-water retention curve which is both continuous and has a continuous slope. The resulting conductivity models generally contain three independent parameters which may be obtained by matching the proposed soil-water retention curve to experimental data. Results obtained with the closedform equations based on the Mualem theory will be compared with observed data for a few soils having widely varying hydraulic properties. THEORETICAL Equations Based on Mualem's Model The following equation was derived by Mualem (1976a) for predicting the relative hydraulic conductivity (Kr) from knowledge of the soil-water retention curve

22,781 citations


"Numerical modelling on fate and tra..." refers methods in this paper

  • ...Hence, the constitutive relationships, as proposed by van Genuchten (1980), represented below by Equations (3)–(5) have been used along with Equation 2 to solve the Richard’s equation: In Equation (4), the term Se represents the effective saturation which is represented as provided in Equation (5)....

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Journal ArticleDOI
TL;DR: In this paper, the authors show that using the mass-conservative method does not guarantee good solutions, since the mass balance errors and erroneous estimates of infiltration depth can lead to large mass imbalance errors.
Abstract: Numerical approximations based on different forms of the governing partial differential equation can lead to significantly different results for unsaturated flow problems. Numerical solution based on the standard h-based form of Richards equation generally yields poor results, characterized by large mass balance errors and erroneous estimates of infiltration depth. Conversely, numerical solutions based on the mixed form of Richards equation can be shown to possess the conservative property, so that mass is perfectly conserved. This leads to significant improvement in numerical solution performance, while requiring no additional computational effort. However, use of the mass-conservative method does not guarantee good solutions. Accurate solution of the unsaturated flow equation also requires use of a diagonal time (or mass) matrix. Only when diagonal time matrices are used can the solution be shown to obey a maximum principle, which guarantees smooth, nonoscillatory infiltration profiles. This highlights the fact that proper treatment of the time derivative is critical in the numerical solution of unsaturated flow.

1,598 citations


"Numerical modelling on fate and tra..." refers methods in this paper

  • ...The time domain was discretised using a backward Euler technique and space domain using a central differencing technique as provided in Equation (10) (Celia and Bouloutas 1990)....

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Book ChapterDOI
01 Jan 1969

1,477 citations

Journal ArticleDOI
TL;DR: In this paper, the theory of secrecy and algebraic inference is used for detecting anomalous soil in Soil Science, and the authors propose a method to detect anomalous soils.
Abstract: THE THEORY OF INFILTRATION: 4. SORPTIVITY AND ALGEBRAIC INFILTRATION EQUATIONS J. PHILIP; Soil Science

1,105 citations


"Numerical modelling on fate and tra..." refers methods in this paper

  • ... Present water flow model (a) verification with Quasi-analytical solution (Philip 1957) (b) verification with analytical solution (Warrick 1985) (refer Table 1 for details) (c) validation with published data from Mitchell and Mayer (1998) (d) validation with published data from Phoon et al. (2007)…...

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Journal ArticleDOI

1,023 citations


"Numerical modelling on fate and tra..." refers methods in this paper

  • ... Present water flow model (a) verification with Quasi-analytical solution (Philip 1957) (b) verification with analytical solution (Warrick 1985) (refer Table 1 for details) (c) validation with published data from Mitchell and Mayer (1998) (d) validation with published data from Phoon et al. (2007)…...

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