Modeling and Analysis of Biofilms Formation and Evolution in Wastewater Treatment Processes using Multi-Agent Systems

Biofilms are complex but omnipresent and industrially important structures. Many studies were devoted to build mathematical models for biofilm analysis but most of them were based on classical continuous approaches. On the other side, only very few studies were directly based on the functional mechanisms to obtain virtual systems which mimic the descriptive observations and allow to predict the state of a biofilm and its possible evolution. This paper will present a non-classical approach based on multi-agent systems for the analysis of biofilm formation. This model shows the spatial repartition of biomass within the biofilm and the impact of the biofilm activity on its environment. Many kind of biofilms can be simulated with the model ; it has been qualitatively validated with the case of the biofilm of an anaerobic wastewater treatment plant. The biomass is modeled by virtual agents that represent micro-colonies of identical bacteria. Each agent follows a mass balance law while its growth is described by a Monod law and its detachment is calculated as a function of its depth in the biofilm and of the level of hydrodynamic forces. The agents interact then with each other to find equilibrium between density and spatial growth. The diffusion-reaction problem has been solved in two dimensions by the Alternating Directions Implicit method. Several simulations are performed to analyze influence of characteristics of the influent liquid phase, for the molecules diffusion in the biofilm and for the biochemical reaction.