Intensification of bioconversion processes: design and development of reactors with high biocatalyst loading

The aim of the research program was to address some open issues related to immobilization of biological systems (enzymes, microrganisms) for bioprocess applications. The research pathway is ultimately targetted at the development of novel and effective tools for bioprocess intensification based on the use of immobilizer biocatalysts. The attention has been specifically focused on two processes: an enzymatic and a microbial process. Conversion of the synthetic dye Remazol Brilliant Blue R (RBBR) by means of crude laccase mixtures from Pleurotus ostreatus. The study aimed at the optimization of the enzymes immobilization protocol and at the characterization of the RBBR conversion by means of free and immobilizer enzymes. The immobilization process was optimized with reference to the covalent binding on granular supports - EUPERGIT C 250L©. In particular, operating conditions were selected so as to maximize the immobilization yield. A reactor for the activity assay of the immobilised enzymes was designed and set-up. The kinetics of RBBR conversion by means of immobilized laccase mixtures was characterised using a purposely designed fixed bed reactor. A kinetic model has been best-fitted against experimental data relative to conversion degree and reactor space-time to assess kinetic parameters. The role of mass transport phenomena between the phases and of adsorption during heterogeneous enzymatic conversion of the dye were investigated. Based on data collected in the experimental campaign and on kinetic models developed, two alternative processes for remediation of dye-bearing wastewaters have been assessed: i) a batch Stirred Tank Reactor (STR) operated with a homogeneous liquid phase containing both the crude laccase mixture and the dye; ii) a Continuous Fixed Bed Reactor (CFBR) loaded with laccases immobilised on EUPERGIT© and continuously fed with the dye-bearing liquid stream. The results highlighted the role played by biocatalyst stability and immobilisation yield on the selection of the best option in terms of the volume of wastewater cumulatively treated in either option. Conversion of the phenol by means of Pseudomonas sp. OX1 biofilm in threephase bioreactors. The study has addressed both experimental and theoretical aspects of the problem. The experimental study has been directed to the assessment of the growth of P. sp OX1 biofilm on silica-based granular supports. Two bench-scale reactor typologies were investigated: a three Phase Circulating (3PC) reactor and an Internal Loop Airlift (ILA) reactor. Tests with the 3PC reactor were directed to optimize the conditions for biofilm growth. Tests with the ILA reactor were aimed at investigating the effect of dilution rate on the performance of the system operated with a mature biofilm that had been previously partly grown up on the solid carrier. The theoretical work has addressed the analysis of the bifurcational and dynamic patterns of an ILA reactor operated with biofilm of P. sp. OX1 attached on granular solids. The role of the growth rate of suspended and immobilised cells using phenol as carbon source, the adhesion rate of suspended cells on carrier surface and the detachment rate of biofilm from the solids carrier were investigated. The dependence of bifurcational patterns on detachment coefficient and dilution rate has been analysed. Results from the theoretical study and from tests carried out with the ILA reactor were compared: the model properly reproduces the functional dependence of the steady state behaviour of the biofilm on the dilution rate observed during the tests.