Simulation of growth and detachment in biofilm systems under defined hydrodynamic conditions

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Abstract
Detachment from biofilms was evaluated using a mixed culture biofilm grown on primary wastewater in a tube reactor. The growth of biofilms and the detachment of biomass from biofilms are strongly influenced by hydrodynamic conditions. In a long‐term study, three biofilms were cultivated in a biofilm tube reactor. The conducted experiments of biofilm growth and detachment can be divided into three phases: 1) an exponential phase with a rapid increase of the biofilm thickness, 2) a quasi‐steady‐state with spontaneous fluctuation of the biofilm thickness between 500 and 1,200 μm in the investigated biofilm systems, and 3) a washout experiment with increased shear stress in three to four steps after several weeks of quasi‐steady‐state. Whereas the biofilm thickness during the homogeneous growth phase can be regarded constant throughout the reactor, it was found to be very heterogeneous during the quasi‐steady‐state and the washout experiments. Growth and detachment during all three phases was simulated with the same one‐dimensional biofilm model. For each of the three phases, a different detachment rate model was used. During the homogeneous growth phase, detachment was modeled proportional to the biofilm growth rate. During the quasi‐steady‐state phase, detachment was described by random detachment events assuming a base biofilm thickness. Finally, the washout experiment was simulated with detachment being a function of the biofilm thickness before the increase of the shear stress. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 81: 607–617, 2003.