Studies on Computer-Aided Design and Analysis of Three-Phase Semifluidized Bed Bioreactors

Attempts have been made to perform computer-aided analysis and simulation of the performance of a three-phase semifluidized bed bioreactor. The bioreactor is of biofilm type. Cocurrent operation with liquid (substrate solution) forming the continuous phase has been considered. Both air and feed solution are thus admitted from the bottom, the air moving up as tiny bubbles. Being semifluidized, the bioreactor is composed of a fully fluidized bed at the bottom and a packed bed at the top. The performance of the bioreactor is analysed by assuming it to be equivalent to two plug flow dispersion reactors (PFDRs) in series, each with a different value of dispersion number/axial dispersion coefficient. The performance equations (assuming dispersed flow) for both sections are written separately and then solved numerically using fourth-order Runge-Kutta method/successive over-relaxation method, based on appropriate boundary conditions. The specific case considered is the aerobic synthesis of Xanthan gum from cheese whey permeate, which follows Contois-type kinetic equation. The fractional gas holdup in both sections, height ratio of fluidized section to packed section and the semifluidization velocity are computed at the outset from selected experimental correlations (compiled from available literature). The results obtained from the developed software package, after verifying experimentally, are used to study and illustrate the performance characteristics of the bioreactor. It is observed that the three-phase semifluidized bed biofilm reactor of proposed design provides substantially large fractional conversion of substrate at large capacities, with relatively low reactor volume requirement.