Determination of steady-states of a bubble column bioreactor with biofilm for aerobic processes

Abstract

The study concerns a bubble column bioreactor with biofilm on its walls in which a microbiological aerobic process occurs. The method of modelling and numerical simulation of this object is presented. The proposed mathematical model of the bioreactor takes into account: axial dispersion of the liquid and gas phase, a microbiological process in the liquid phase and the biofilm, mass transfer from the gas to the liquid and from the liquid to the biofilm, internal mass transfer resistance in the biofilm and biofilm detachment. It was shown that the system of differential equations is characterised by a large stiffness ratio exceeding 1015. Two algorithms for the determination of steady-states were proposed and compared. The one based on orthogonal collocation on finite elements used for solving the equations of liquid, gas phases and the biofilm is effective in contrast to the one based on the shooting method. It was shown that the biofilm presence positively influences the bioreactor properties, including the reduction of the substrate inhibiting effect by elimination of steady-state multiplicity.