Mise au point d'un fermenteur de laboratoire grâce à un micro-ordinateur de faible coût

Abstract - Setting up of a laboratory computerized bioreactor
This publication describes a computerized bioreactor combining conventional regulation systems and the possibilities of a low cost personal computer with additional commercial interfaces. The computer controls temperature, pH, dissolved oxygen, agitation speed, nutrient supplies and sampling. It fulfills the functions of set-point controlling, data storage, curve plotting, mathematical processing and manages the experimental file.
The connection of a bioreactor to a computer not only allows a precise knowledge of the environmental conditions but also opens a large field of possibilities, including the constitution of a data bank, on-line and off-line calculations and feedback control. We show here that the evolution of instrumentation, electronic and computer techniques, combined with the special characteristics of fermentation, enable a laboratory bioreactor to be upgraded by a personal computer.
The choice of the computer should be based primarily on the criteria of rapidity, memory capacity, reliability and possibilities of interfacing. Configuration as a set-point controller for monitoring fermentation experiments imposes few restrictions on the first three points. Computer connection is more and more designed into fermentation material, and some microcomputers possess multiple plug-in boards.
The software is written in BASIC with a few subroutines in machine langage. The originality of the on-line program resides in a mixed structure between a synchronous interruption program and the asynchronous main program. This simple structure enables the 16 channels to be read, calculations to be performed, measurements to be displayed and curves to be updated every two seconds, which is better than needed for fermentation experiment.
The main purpose of the bioreactor is the control of the growth of mixed culture of lactic acid bacteria. But we present two applications dealing with oxygen wich are related to controlling the superficial flora of cheese:
for calibration of dissolved oxygen probe, the classical way (in % of saturation) is far from being perfect since the quantity of dissolved oxygen at saturation depends on temperature, pressure and composition of the medium. An absolute and reproductible calibration (in mg O₂ / l of solution) can be obtained by the use of a very simple program. All that is required is to enter the temperature and the composition of the medium ;
the gas-liquid transfer coefficient kιa is part of the basic characteristics of an installation. It may be measured with chemical or enzymatic methods, or by a static or a dynamic method with a dissolved oxygen probe. The program used allows dynamic calculation of kιa during fermentation.

Résumé - Cette note montre qu'il est possible de compléter un fermenteur de laboratoire par un micro-ordinateur de faible coût du type " ordinateur individuel " complété par des interfaces du commerce. Le calculateur contrôle la température, le pH, l'oxygène dissous, la vitesse d'agitation, un apport de nutriments et l'échantillonnage. Il remplit les fonctions de superviseur et de stockage, de tracé de courbes et de traitement mathématique, et gère le fichier d'expérience.
Deux applications sont présentées : étalonnage universel d'une sonde à oxygène dissous et mesure dynamique du kιa d'un fermenteur.