Assessment of Diffusion Limitations on the Performance of Immobilised Acid Urease Derivatives

Abstract

In this work, the specific activity of acid urease immobilised on Eupergit^® C250L at different enzyme loadings Y_P/B in the range of 48-170.5 mg BSAE/g dry support (ds) was satisfactorily reconstructed by using the simultaneous film and intraparticle diffusion and Michaelis-Menten kinetic reaction model. By referring to the intrinsic kinetic parameters of free acid urease, the statistically significant change in the apparent affinity of immobilised enzyme for urea was attributed to diffusion limitations only. When operating in a stirred bioreactor in the pseudo-first order regime, the specific activity of the biocatalyst was mainly restricted by its internal resistance, the corresponding effectiveness factor (?) reducing from 0.9 to 0.28 as Y_P/B increased from 12.5 to 400.0 mg BSAE/g ds. The combined effect of internal and external mass-transfer resistances limited the advantages of using biocatalysts with enzyme loadings greater than 150 mg BSAE/g ds.