Bernardo Ruggeri

Citric acid production by A. niger with banana extract

Abstract Experimental runs were carried out on citric acid bioproduction using banana extract as carbon source. The micro-organism used was a strain of Aspergillus niger. Different types of batch bioreactor were tested: bubble column (BCR) and stirred tank reactor (STR). With the STR the effects of two different impeller types were studied: Rushton six-bladed turbine and Lightnin A310 turbine, both at various rotational speeds. During the tests various parameters were measured: biochemical (biomass as w/v and mean mould pellet diameter), chemical (total sugar and citric acid concentration) and physical (dissolved oxygen tension, DOT; oxygen uptake rate, OUR; viscosity; gas/liquid volumetric mass transfer coefficient, KLa). The results showed that citric acid production is strictly connected to the morphology of the microorganism; the mould must grow in pellet form, as occurs when a gentle agitation is provided such as in the BCR; otherwise, with mechanical agitation the pellets are broken, the biomass morphology becomes filamentous and the citric acid production markedly decreases. The fermentation results are discussed to achieve a better comprehension of the main influential parameters for process scale-up.

SUPPORTED LIQUID-PHASE REACTOR (SLPR) FOR PCBS IN OIL DECONTAMINATION

Abstract Polyethyleneglycols containing a dissolved based and a radical initiator are supported on a solid carrier in a fixed bed reactor. This formulation is able to degrade chemically stable polychlorinated diphenyls (PCBs) dissolved in transformer oil in a continuous process. This short report concerns with the results of laboratory and on-site applications of chemical PCBs degradation by SLPR.

A holistic view of (bio)kinetics

Abstract The present paper aims to formalize the use of a macro-approach to describe the kinetics of complex (bio)reactions. The reasons for a holistic approach are outlined in order to propose the fuzzy modelling as a mathematical framework able to handle the holistic parameters in bioreactor description. Two examples are discussed to highlight the peculiarities and the power of the methodology. Particular attention is devoted to a comparison of the traditional approach and the fuzzy one to describe the kinetic behaviour of a biocatalyst in a bioreactor.

Mass transfer and observed activity for entrapped biomass

Abstract Several tests aimed at evaluating the mass transfer affects on the activity of the entrapped cells were carried out in a Stirred Batch Reactor (SBR) and in a Continuous Fixed Bed Reactor (CFBR). S. cerevisiae, either as free yeast or entrapped in an alginate matrix under anaerobic condition was used. A comparison between free and entrapped biokinetics is outlined. Entrapped yeast shows a remarkable decrease of activity compared to the free cells. For both SBR and CFBR, the application of different methodologies confirms that mass transfer phenomena are not controlling the bioreaction.