Modelamiento de la transferencia de calor y masa (agua) en un biorreactor de charolas para fermentación en medio sólido. Capítulo 3: Justificación. [Modeling of heat and mass (water) transfer in tray bioreactor for solid-state fermentation. Chapter 3: Justification] (original) (raw)

In this paper we developed a mathematical model for predicting temperature and moisture content profiles in the bed of a tray bioreactor for solid-state fermentation (SSF). For this purpose we developed heat and mass (water) balances which considered the mainmechanisms of heat and mass transfer in the fermentation bed. These balances were used to estimate the heat and mass (water) transfer coefficients. Bioreaction was also proposed for substrate consumption, biomass generation, CO2 and water. Stoichiometric balances were carried out to describe the growth of microorganisms. We used two strains, Aspergillus niger AT for fermentations (runs) on substrate support (70%, wheat bran; 30%, soybean meal) and Aspergillus niger C28B25 for fermentations on inert support (perlite). In the runs on substrate-support, CO2 production and fermentation bed temperature (no data storage) were on-line measured and initial and final moisture content of fermentation bed, water activity, pH and enzyme activity phytase were off-line measured. In the runs on inert support, CO2 production and fermentation bed temperature (both data storage), were measured and at regular time intervals, moisture, water activity, pH, enzymatic activity of invertase, biomass concentration, substrate concentration were off-line measured. The online measurement of CO2 production in the process was important because from these data, we estimated metabolic water generation, biomass and metabolic heat generation using the proposed bioreactions. Ordinary differential equations obtained from the water and energy balances allowed predictions of temperature and moisture content profiles in the fermentation bed of tray bioreactor. The system of ordinary differential equations was solved using the algorithm "Runge-Kutta.Fehlberg" (RKF56) Polymath ® software version 6.0. Integral mass and energy balances made possible to estimate the coefficients of heat and mass transfer (water) during the growth of microorganisms, which were used later in the mathematical model proposed.The profiles predictions obtained with the model for temperature and moisture content in fermentation bed, showed good fit compared with the experimental data for different operating conditions in the tray bioreactor. As a strategy for removing metabolic heat from the bed of fermentation the use of a fan system is proposed to change the air flow conditions in the bioreactor headspace (air space within the bioreactor that is not within the matrix of the substrate), the variations caused by internal forced air circulation were defined by the Reynolds number (NRe). The effect of the NRe and fermentation bed height (operation variables) on the variables described above were evaluated. This study was conducted in both support-substrate as inert support. In the studies with substrate support and inert support carried out was found that the increase in bed height leads to higher accumulation of heat in the fermentation bed affecting negatively to the enzyme activities. The increase in the NRe had a positive effect in heat removal, improving the enzyme activities, however, must be found an optimum value, since the use of high values of NRe causes drying of fermentation bed that affect adversely the enzyme activities.