Development and experimental evaluation of a steady‐state, multispecies biofilm model

A steady‐state model for quantifying the space competition in multispecies biofilms is developed. The model includes multiple active species, inert biomass, substrate utilization and diffusion within the biofilm, external mass transport, and detachment phenomena. It predicts the steady‐state values of biofilm thickness, species distribution, and substrate fluxes. An experimental evaluation is carried out in completely mixed biofilm reactors in which slow‐growing nitrifying bacteria compete with acetate‐utilizing heterotrophs. The experimental results show that the model successfully describes the space competition. In particular, increasing acetate concentrations causes NH₄⁺‐N fluxes to decrease, because nitrifiers are forced deeper into the biofilm, where they experience greater mass‐transport resistance.