One-dimensional mixed-culture biofilm model considering different space occupancies of particulate components.

A new one-dimensional mixed-culture biofilm model was derived based on a hypothesis that each particulate component would have different space occupancy within biofilm. Contrary to conventional density-based modeling approaches, in this model the volume change of the biofilm is described with the space occupancies of the particulate components, new model parameters introduced here. The unique feature of this model is that internal pore development during biofilm growth can be predicted implicitly so that the changes of effective diffusivities of soluble components depending on internal porosity are readily implemented in the model. Simulation studies revealed that the presented biofilm model could reasonably describe several important aspects of biofilm growth phenomena. In a mixed-culture biofilm system where heterotrophs and autotrophs were involved, the overall biofilm growth pattern was governed by microbial competition depending on influent composition. In a thick heterotrophic biofilm, a simulated biomass distribution and internal porosity profile showed higher total biomass concentration, lower active cell fraction, and lower internal porosity in the bottom layers of the biofilm, which are well coincident with the experimental data reported previously. All these phenomena can be explained by the proceeding of biofilm consolidation, which happens due to the inter-conversions of the particulate components having different space-occupancy values. The presented biofilm model suggests that the space occupancy of EPS may be a key model parameter to decide the overall biofilm growth pattern by regulating the extent of biofilm consolidation.