In the present study, extensive experimental investigations and detailed theoretical analysis of a two-dimensional packed bed bioreactor, employed for the production of galacto-oligosaccharides (GOS) from milk whey were performed. Model equations, in one- and two-dimensions, capable of predicting the substrate concentration distribution in the bioreactor were developed by coupling mass balance equation with appropriate velocity distribution equation and solved numerically. Validation of the proposed model equations was done by a set of experimental data obtained from the bioreactor. The effects of reactor to catalyst particle diameter ratio (d t/d p), feed flowrate (10(-6)-10(-9) m(3) s(-1)), and initial lactose concentration (50-200 kg m(-3)) on substrate concentration distribution were investigated in detail. While, the distribution of substrate concentration in axial direction was independent of d t/d p, it was observed that for d t/d p <40, significant radial concentration distribution existed. It was further observed that the substrate conversion and product yield obtained experimentally showed an excellent agreement (97 ± 2 %) with the results predicted by the two-dimensional model equation, whereas, the results predicted by the one-dimensional model equation did not lie within the desired confidence level (<90 %). The results were confirmed by both curve fitting and statistical analysis. The prediction of substrate concentration distribution in axial and radial directions using the developed two-dimensional model equation is necessary for computing the bioreactor volume to achieve the desired GOS yield.
Keywords: Immobilized enzymes; Modelling; Packed bed bioreactors; Radial average conversion; Two-dimensional analysis; Whey.