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 ext ended physical systems, and represent an alternative to the classical PDE a pproach. In this paper a macroscopic cellular automata model for simulating the bioremediation of contaminated soils is introduced. The choice of macr oscopic automata is motivated by the aim to simulate large-scale systems. I t is suggested that in some cases, where the basic laws of continuum mechan ics cannot be directly applied without adding phenomenological assumptions, and where the equation system is not amenable to analytical solution, dire ct discrete modelling may represent a convenient alternative to the use of continuum models, followed by numerical discretization. This hypothesis is empirically tested in the bioremediation case. The model describes the bioremediation of contaminated soils, which relies upon the use of indigeneous microorganisms to degrade the contaminant: bior emediation models pose particular challenges as several physical, chemical and biological phenomena interact in a disordered and partially unknown mat rix (the soil). The model is hierarchical, and is composed by a fluid dynam ical layer, a solute description layer and a biological layer. The model ha s been tested in a pilot plant, in the case of contamination by phenol. The values of the phenomenological parameters have been determined by the use of genetic: algorithms. The model has proven capable to carefully describe experimental results in a wide range of experimental conditions. It has als o been run on a MIMD parallel architecture, achieving a high speed up. It t herefore represents an example of application of cellular automata to a rea l-world problem which has a very high social and economic importance, and w here progresses in modelling may greatly improve the effectiveness of the d econtamination interventions. (C) 1999-Elsevier Science B.V. All rights res erved.