Modelling Microbial Degradation Coupled to Reactive Transport in Groundwater: A Benchmark Analysis
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Modelling Microbial Degradation Coupled to Reactive Transport in Groundwater: A Benchmark Analysis Clara Sena · Jorge Molinero · Shuji Ajima · Norifumi Todaka
Received: 12 January 2011 / Accepted: 17 November 2011 / Published online: 22 December 2011 © International Association for Mathematical Geosciences 2011
Abstract Microbes are ubiquitous in groundwater systems, and they play an important role in the redox state of groundwater and especially on the fate of organic contaminants. In this context, numerical simulations that couple microbial processes to reactive transport models are becoming more popular. In the present work, we revisit the mathematical ground of microbial redox reactions and perform a benchmark analysis of the simulation of aerobic benzene degradation in a shallow and oxidizing aquifer. Numerical results indicate that the two codes tested (one using the finite elements approach and the other using the finite differences approach) lead to very similar results. In addition, the coupling of heterogeneous geochemical reactions to the benchmarked example problem provides a solid basis for the understanding of the redox reactions and the changes on the carbon system triggered by the aerobic degradation of benzene. Keywords Microbial activity · Reactive transport · Geochemical processes · BIOCORE · Geochemist’s workbench 1 Introduction Reactive transport models are used worldwide to simulate groundwater flow and the transport of solutes coupled to biogeochemical reactions. These simulations are used C. Sena () CVRM/Geo-Systems Centre – Instituto Superior Técnico, Avenida Rovisco Pais, 1049-001 Lisbon, Portugal e-mail: [email protected] C. Sena · J. Molinero Amphos 21 Consulting S.L., Passeig de Gracía i Faria, 49-51, 08019 Barcelona, Spain S. Ajima · N. Todaka Electric Power Development Co., Ltd., 15-1, Ginza 6-Chome, Chuo-ku, Tokyo 104-8165, Japan
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Math Geosci (2012) 44:209–226
Fig. 1 Sketch of a hydro-bio-geochemical system where the main heterogeneous and homogeneous reactions are illustrated. The curved arrows illustrate the possible fluxes of chemical species between different phases: gas, aqueous, solid, and biomass
in many different contexts such as the evolution of natural systems (Canavan et al. 2007; Steefel and Lichtner 1998; Thullner et al. 2005; Wang and Van Cappellen 1996); laboratory experiments (Pérez-López et al. 2009; Postma and Appelo 2000); large scale experiments (Molinero and Samper 2006; van Breukelen et al. 1998); acid mine drainage (Acero et al. 2009; Bain et al. 2000; Brookfield et al. 2006); the fate of contaminants in the environment (Christensen et al. 2000), among many others. Geochemical reactions can be homogeneous reactions, meaning that the reactions take place within a single phase (e.g. redox reactions in the aqueous phase, aqueous complexation, acid-base reactions), or heterogeneous reactions in which a species undergoing a given transformation is transferred from one phase to another (Fig. 1). Precipitation reactions where a solute is transferred from the
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