Discrete-differential modelling of biofilm structure

A fully quantitative two- and three-dimensional approach for biofilm growth and structure formation has been developed. The present model incorporates the flow over the irregular biofilm surface, convective and diffusive mass transfer of substrate, bacterial growth and biomass spreading. A future model will also include a mechanism for biofilm detachment due to biofilm deformation stress. Any arbitrary shape of the carrier surface can be accommodated in the model, as well as multispecies and multisubstrate biofilms. Results of model simulations show that the ratio between nutrient transfer rate to the biofilm and the bacterial growth rate influences to a great extent the biofilm roughness and porosity. A low mass transfer rate, i.e., low Reynolds numbers or high values of Thiele modulus, results in the development of a rough and open biofilm. When the biofilm growth is not limited by the substrate availability but by the rate of bacterial metabolism, the biofilm forms as a compact and homogeneous structure. The multidimensional biofilm modelling approach we used is very suitable for theoretical investigation of factors that affect biofilm structure and ecology. (C) 1999 IAWQ Published by Elsevier Science Ltd. All rights reserved.