MODELING BIOFILMS

Because all levels of biofilm models are useful depending on the application, this chapter describes and discusses biofilm modeling starting from the simple, homogeneous case to the more complex, structurally and functionally heterogeneous cases. Obviously, the complexity of the model is reduced when a single-species biofilm is modeled (i.e., a functionally homogeneous but structurally heterogeneous biofilm); thus, the discussions in the chapter focus on this simplified problem. In the cellular automata (CA) biofilm model, there are two superimposed lattices, one of them containing information on the location of food particles (substrate lattice) and the other one describing the location of microbial particles (microbial lattice). The simulation of biofilm activity is done by evaluating these stochastic processes over a series of time steps. A section describes the fundamental rules for these stochastic processes and their relation to the physical and biological parameters that represent the biofilm system. Biofilm erosion at the surface, another possible process controlling biofilm growth, can be implemented by selecting a maximum biofilm height, beyond which any microbial outgrowth will be removed from the biofilm. The evolution of biofilm modeling from the 1970s until now shows different approaches to the mathematical abstraction of the biofilm problem, but it is evident that the conceptual basis for all the models is similar and relies on mathematically coupling substrate diffusion with substrate utilization, microbial growth, and microbial decay or detachment.