Modelo de piret

A Kinetic Model for Gluconic Acid Production by *

Aspergillus niger

H. ZNAD, M. BLAŽEJ, V. BÁLEŠ, and J. MARKOŠ**

Department of Chemical and Biochemical Engineering, Faculty of Chemical and Food Technology, Slovak University of Technology, SK-812 37 Bratislava e-mail: jozef.markos@stuba.sk Received 10 April 2003

Fermentation kinetics of gluconic acid production by Aspergillus nigerwas studied in a batch system. The dependence of the specific growth rate on carbon and oxygen substrates was assumed to follow either the Monod or Contois kinetic model. The simulation results revealed that for predicting the fermentation process of gluconic acid production by A. niger, the Contois type model was more suitable than that based on the Monod equation. The Luedeking—Piret equation wasproposed for gluconic acid production and an equation considering the cell maintenance for glucose and dissolved oxygen consumption. Estimated parameters of this model indicate that the production of gluconic acid was mostly growth-associated.

Gluconic acid and its salts are important materials widely used in pharmaceutical, food, feed, detergent, textile, leather, photographic, and concreteindustries [1—3]. There are different approaches available for the production of gluconic acid: chemical, electrochemical, biochemical, and bio-electrochemical processes [4—6]. Fermentation is one of the dominant routes for manufacturing gluconic acid at present [7]. Gluconic acid fermentation by A. niger belongs to aerobic fermentations with high oxygen demand. The biotransformation of glucose togluconic acid represents a simple dehydrogenation reaction without involvement of complex metabolic cell pathways, which is realized with a high selectivity, high rate, and high yield of conversion. The development of kinetic models consists of comparing assumed models with experimental data in order to obtain more relevant equations. Kinetic models enable the bioengineer to design and controlmicrobial processes [8]. In predicting the behaviour of these processes, mathematical models, together with carefully designed experiments, make it possible to evaluate the behaviour of systems more rapidly than with solely laboratory experiments. Mathematical models for a microbial process can be developed using two different mechanisms. Thus structured and unstructured models can be obtained [9].Structured models take into account some basic aspects of cell structure, function, and composition. In unstructured models,

however, only cell mass is employed to describe the biological system. In this study, an unstructured model for cell growth, product formation, glucose consumption, and dissolved oxygen was found to be convenient to characterize the fermentation process. In modellingfermentation systems, it is relatively easy to set up a system of differential equations to represent the bioprocess dynamics. The most difficult part in modelling the fermentation process is obtaining the form of the specific growth rate expression µ that best represents the observed kinetic behaviour. Many investigations have been carried out on the modelling of gluconic acid by A. niger. Takamatsu et al.[10] reported the structured model to describe gluconic acid fermentation by A. niger. Liu et al. [11] proposed a simple unstructured model using the logistic equation for growth. Reuss et al. [12] developed a comprehensive model, they found that due to the excess of glucose and oxygen during the active growth period, these two components need not be considered in the µ. However, none of themconsidered the effect of the two important substrates (glucose and dissolved oxygen) in the µ used. In this study, suitable kinetic models for the production of gluconic acid by A. niger in a fermentation process carried out in mechanically stirred bioreactors with the volumes of 2 dm3 and 5 dm3 have been suggested taking into account the glucose and dissolved oxygen in the µ.

*Presented at the 30th...