Modeling and simulation of competition between two microorganisms for a single inhibitory substrate in a biofilm reactor

A simple biofilm model was developed to simulate the competition between tw o microorganisms for a common inhibitory substrate. The following assumptio ns were made for the simulations: (1) the biofilm has a uniform thickness a nd is composed of 5 segments, (2) growth of two microorganisms A and B whic h utilize the common substrate is expressed by the Haldane kinetics with a spatial limitation term and is independent of the other microorganism in th e biofilm reactor, and (3) diffusion of the substrate, movement of the micr oorganisms, and continuous loss of the biomass by shearing are expressed by Fick's Law-type equations. The qualitative behavior of the biofilm reactor is characterized by five regions, I-V, depending on the operation conditio ns, the substrate concentration in feed, and the dilution rate. In region I , both microorganisms are washed out of the biofilm reactor. In region II, microorganism B is washed out, and in region Iii, microorganism A is washed out of the biofilm. In region IV, both microorganisms coexist with one ano ther. In region V, both microorganisms coexist with a sustained oscillatory behavior. Convergence to regions I-V depends on the initial conditions. In regions Il-V, washout of either or both microorganisms is also observed wi th initial conditions too far away. (C) 1999 John Wiley & Sons, Inc.