INTERNAL AIRLIFT BIOREACTOR FOR GLUCONIC ACID PRODUCTION-MODELLING AND SIMULATION

Abstract

The airlift reactors have potential applications in biotechnology industries due to their simple construction and less shear stress imposed on shear sensitive cells compared with the mechanically stirred tanks. A tanks-in-series model and axial dispersion model are applied for mathematical modelling of the unsteady state performance of a batch operation in a 4.5 dm3 internal loop airlift bioreactor for the production of gluconic acid by fermentation. Tanks-in-series model consists of a set of simultaneous (176 equations for 44 stages) first order ordinary differential equations obtained from material balances of cell mass, product, substrate and dissolved oxygen around the hypothetical well mixed stages in the bottom, riser, top and down comer sections of an airlift reactor. In axial dispersion model each zone of the reactor is modelled separately according to mixing properties within (ideal mixing or plug flow with axial dispersion). These equations are solved simultaneously using ODE solver of MATLAB. Logistic and contois models used for kinetics are compared for prediction of time dependent concentration profiles of biomass, gluconic acid, glucose and dissolved oxygen in an airlift reactor. Both models have been validated with experimental data of Znad et al (2004). Validated logistic and contois models are used to predict the effect of change in initial biomass concentration (X0) and airflow rate (Qg), on the performance of gluconic acid production in airlift reactor. Effect of number of stages in tanks in series model and axial dissolved oxygen profile were investigated. The model is simple enough to be used in design studies and it can be adapted to airlift system configurations and fermentation systems other than gluconic acid fermentation.