Oxygen- And Nitrate-based Biodegradation OfAromatic Hydrocarbons Using Monod-kinetics:Application Of A Simplified Numerical Algorithm (original) (raw)
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Journal of Contaminant Hydrology, 1999
Bioremediation has become an important remediation technology during the past few years. However, limited understanding of processes, data limitations and parameter uncertainty, and computationally intensive numerical solutions have reduced the interest to perform detailed field-scale modeling, especially with non-linear Monod expressions. In this paper, the focus was computational efficiency where a simplified numerical algorithm was developed to solve the non-linear reactions between the hydrocarbon, oxygen, nitrate, and a heterotrophic facultative microbial population. The numerical algorithm was presented using a commonly adapted conceptual model of reaction kinetics between different species with multi-term Monod expressions. The accuracy and efficiency of the algorithm were tested with an iterative solution using the Runge-Kutta method. Simulation results obtained from reaction only and one-dimensional advection-dispersion-reaction transport examples showed good accuracy while maintaining numerical stability. In general, the accuracy increased with contaminant concentrations relatively higher than the corresponding half-saturation constant. Also, the simplified algorithm is found to be much more computationally efficient than the iterative technique. The gain in computational efficiency was at least threefold and this gain increased with the increase of time step. Future work will explore the efficiency and accuracy of the proposed simplified algorithm with field-scale scenarios related to intrinsic and enhanced bioremediation. q 0169-7722r99r$ -see front matter q 1999 Elsevier Science B.V. All rights reserved.
Computing and Visualization in Science, 2004
In this work we present and analyze a reliable and robust approximation scheme for biochemically reacting transport in the subsurface following Monod type kinetics. Water flow is modeled by the Richards equation. The proposed scheme is based on higher order finite element methods for the spatial discretization and the two step backward differentiation formula for the temporal one. The resulting nonlinear algebraic systems of equations are solved by a damped version of Newton’s method. For the linear problems of the Newton iteration Krylov space methods are used. In computational experiments conducted for realistic subsurface (groundwater) contamination scenarios we show that the higher order approximation scheme significantly reduces the amount of inherent numerical diffusion compared to lower order ones. Thereby an artificial transverse mixing of the species leading to a strong overestimation of the biodegradation process is avoided. Finally, we present a robust adaptive time stepping technique for the coupled flow and transport problem which allows efficient long-term predictions of biodegradation processes.
Stochastic analysis of oxygen- and nitrate-based biodegradation of hydrocarbons in aquifers
Journal of Contaminant Hydrology, 2000
A Lagrangian stochastic framework was used to analyze field-scale aerobic biodegradation in a heterogeneous aquifer, using Monod-kinetics based reactions between the contaminant, oxygen and microbes. Subsurface heterogeneity was represented by closed-form travel time distributions, derived from a spatially correlated random hydraulic conductivity field with a log-normal distribution. The solution to the coupled and nonlinear, one-dimensional Lagrangian transport equations was obtained using the operator-splitting technique. The presence of nitrate, and considering nitrate as a second electron acceptor, produced significantly different results under intrinsic conditions for different scales of heterogeneity and sorption. In general, nitrate as a second electron acceptor can substantially lower the peak contaminant concentration and increase the maximum remediation under various conditions of heterogeneity and sorption. There exists a critical value for retardation coefficients of both contaminant and microbes that produce complete Ž . degradation of mass, and this value depends on the availability of the electron acceptor s and is independent of the heterogeneity. Maximum remediation and peak contaminant concentration were sensitive to half-saturation constants. Enhanced remediation using oxygen and nitrate showed that maximum remediation can be increased by approximately 15% when oxygen or nitrate concentration was increased by 50%, but a further increase may be obtained if injection occurred at a more effective location. The proposed stochastic methodology is capable of analyzing field-scale biodegradation using multiple electron acceptors in a simple and computationally attractive manner, producing useful results on design parameters. The key contributions arising from the Lagrangian stochastic framework in field-scale analysis, its limitations and potential approaches for overcoming these limitations are also discussed. q 0169-7722r00r$ -see front matter q 2000 Elsevier Science B.V. All rights reserved.
Hydrological Processes, 1999
Microbiological degradation of perchloroethylene (PCE) under anaerobic conditions follows a series of chain reactions, in which, sequentially, trichloroethylene (TCE), cis-dichloroethylene (c-DCE), vinylchloride (VC) and ethene are generated. First-order degradation rate constants, partitioning coecients and mass exchange rates for PCE, TCE, c-DCE and VC were compiled from the literature. The parameters were used in a case study of pump-and-treat remediation of a PCE-contaminated site near Tilburg, The Netherlands. Transport, non-equilibrium sorption and biodegradation chain processes at the site were simulated using the CHAIN_2D code without further calibration. The modelled PCE compared reasonably well with observed PCE concentrations in the pumped water. We also performed a scenario analysis by applying several increased reductive dechlorination rates, re¯ecting dierent degradation conditions (e.g. addition of yeast extract and citrate). The scenario analysis predicted considerably higher concentrations of the degradation products as a result of enhanced reductive dechlorination of PCE. The predicted levels of the very toxic compound VC were now an order of magnitude above the maximum permissible concentration levels.
Communications in Numerical Methods in Engineering, 2001
A fully coupled numerical model is presented which describes biodegradation kinetics and NAPL-aqueous two-phase flow in porous media. The set of governing partial differential equations is split in two subsystems, the former one in terms of phase pressure and saturations, and the latter one in terms of contaminant concentration and bacterial population distribution. Non-linear saturation dependence in Brooks–Corey relative permeability functions and capillary pressure effects are incorporated in a mixed-hybrid finite element model. The non-linear degradation kinetics à la Monod is taken into account as a source term in the finite-volume discretization of the equation modelling contaminant transport. The global coupling is performed by using a nested block-iteration technique. A set of numerical experiments demonstrates the effectiveness of the method. Sensitivity analysis results are also presented. Copyright © 2001 John Wiley & Sons, Ltd.
In-situ Bioremediation modeling of organic contaminant
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Estimation of Sequential Biodegradation Product Rate Constants
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