Applying cellular automata to complex environmental problems: the simulation of the bioremediation of contaminated soils

Cellular automata can be applied to modelling the dynamics of spatially extended physicalsystems, and represent an alternative to the classical PDE approach. In this paper a macroscopiccellular automata model for simulating the bioremediation of contaminated soils is introduced.The choice of macroscopic automata is motivated by the aim to simulate large-scale systems.It is suggested that in some cases, where the basic laws of continuum mechanics cannot bedirectly applied without adding phenomenological assumptions, and where the equation systemis not amenable to analytical solution, direct discrete modelling may represent a convenientalternative to the use of continuum models, followed by numerical discretization. This hypothesisis empirically tested in the bioremediation case.The model describes the bioremediation of contaminated soils, which relies upon the use ofindigeneous microorganisms to degrade the contaminant: bioremediation models pose particularchallenges as several physical, chemical and biological phenomena interact in a disordered andpartially unknown matrix (the soil). The model is hierarchical, and is composed by a fluiddynamical layer, a solute description layer and a biological layer. The model has been testedin a pilot plant, in the case of contamination by phenol. The values of the phenomenologicalparameters have been determined by the use of genetic algorithms. The model has proven capableto carefully describe experimental results in a wide range of experimental conditions. It has alsobeen run on a MIMD parallel architecture, achieving a high speed-up. It therefore representsan example of application of cellular automata to a real-world problem which has a very highsocial and economic importance, and where progresses in modelling may greatly improve theeffectiveness of the decontamination interventions.