A kinetic approach for simulating redox‐controlled fringe and core biodegradation processes in groundwater: model development and application to a landfill site in Piedmont, Italy

Abstract

Abstract:A three-dimensional model for predicting redox controlled, multi-species reactive transport processes in groundwater systems is presented. The model equations were fully integrated within a MODFLOW-family reactive transport code, RT3D. The model can simulate organic compound biodegradation coupled to different terminal electron acceptor processes. A computational approach, which uses the spatial and temporal distribution of the rates of different redox reactions, is proposed to map redox zones. The method allows one to quantify and visualize the biological degradation reactions occurring in three distinct patterns involving fringe, pseudo-core and core processes. The capabilities of the numerical model are demonstrated using two hypothetical examples: a batch problem and a simplified two-dimensional reactive transport problem. The model is then applied to an unconfined aquifer underlying a leaking landfill located near the city of Turin, in Piedmont (Italy). At this site, high organic load from the landfill leachate activates different biogeochemical processes, including aerobic degradation, denitrification, manganese reduction, iron reduction, sulfate reduction and methanogenesis. The model was able to describe and quantify these complex biogeochemical processes. The proposed model offers a rational framework for simulating coupled reactive transport processes occurring beneath a landfill site.

On the importance of diffusion and compound-specific mixing for groundwater transport: An investigation from pore to field scale

“…For organic compounds typically present in contaminated groundwater, the most important biochemical processes are microbially-mediated redox reactions. Microorganisms can degrade oxidizable organic pollutants through a number of redox processes involving different terminal electron acceptors (e.g., Chapelle et al, 1995;Christensen et al, 2001;Rolle et al, 2008). Favorable conditions for some important degradation reactions occur at the fringe of contaminant plumes where soluble electron donors and acceptors come into contact through mixing between the contaminant and the surrounding ambient water.…”

Biological reduction of chlorinated solvents: Batch-scale geochemical modeling

“…As outlined in Table 1, the model accounts for e-donor fermentation, dechlorination of chlorinated ethenes, competing TEAPs (e.g., sulfate and iron reduction), growth and decay of multiple microbial communities, pH and alkalinity, mineral precipitation/dissolution, gas formation, and mass transfer of species between non-aqueous and aqueous phases. Although other complex models with comparable features exist, for example models that integrate the dependency of the reaction kinetics on the concentration of solutes [24,94], explicitly simulate growth and decay of bacteria [81] and account for pH-dependent bacterial growth [11], these complex biogeochemical models were applied in systems such as landfill leachate aquifer plumes and BTEX (benzene, toluene, ethylbenzene and xylene) spills [11,12,[79][80][81]88]. The presented model is the first that accounts explicitly for reductive dechlorination by microbial communities as well as detailed soil-water geochemistry.…”

Metal speciation in landfill leachates with a focus on the influence of organic matter

“…Regarding the first drawback, among the three criteria presented above that underlie the concept of K d , the third one is particularly questionable in a context of leachate migration in the vicinity of a landfill, as shown by several authors (e.g. Rolle et al, 2008;. Regarding the second drawback, the K d approach accounts for retardation of pollutant migration, but does not yield an effective attenuation of long-term groundwater concentrations, compared to the situation without retardation, because attenuation mechanisms such as pollutant co-precipitation with mineral phases are not taken into account.…”