| This research starts with a critical review of the relationships among three microbial products: extracellular polymeric substances (EPS), soluble microbial products (SMP), and inert biomass. The development of a unified theory couples them and reconciles apparent contradictions. A mathematical model quantifies the relationships among the microbial products, active biomass, original substrate and an electron acceptor. The model is solved with a set of parameters appropriate to the experimental study of Hsieh et al. (1994), and it captures all the trends in the experimental data.; The Unified Multi-Component Cellular Automaton (UMCCA) model predicts quantitatively the development of the biofilm's composite density for three biofilm components—active bacteria, inert biomass, and EPS—and the concentrations of three soluble organic components (soluble substrate and two types of SMP) and oxygen. The UMCCA model introduces the novel feature of biofilm consolidation. Each biofilm compartment in the model output consolidates to a different degree that depends on the age of its biomass. The UMCCA model also adds a cellular-automaton algorithm that identifies the path of least resistance and directly moves excess biomass along that path, thereby ensuring that the excess biomass is distributed efficiently. Some major trends that the UMCCA model shows are that the top of the biofilm is dominated by active biomass and EPS, while the bottom is dominated by residual inert biomass, that the top of all biofilms is quite “fluffy,” and that all biomass types show considerable local heterogeneity. The UMCCA model is solved for conditions similar to the experiments of Bishop et al. (1995) and shows all the major trends in the experimental data. These comparisons support the importance of including the novel features of the UMCCA model, i.e., multiple biomass components and consolidation.; Finally, the capabilities of UMCCA are expanded to also calculate different mechanical properties throughout the biofilm, which is modeled as an elastic, isotropic, and non-homogeneous material, with its properties (a composite Young's modulus) depending on the concentration of the biofilm solid components. The ABAQUS finite-element software is used to determine the stresses and strain throughout a simple prototype biofilm. |
