Mohammad Ali Fanaei - Chemical Engineering Department, Engineering Faculty, Ferdowsi University, Mashad, I.R. Iran
Behrooz Mahmoodzadeh Vaziri - Chemical Engineering Department, Engineering Faculty, Islamic Azad University, Quchan, I.R. Iran

Normal operation of packed-bed bioreactors used for solid-state fermentation involves a static bed aerated from the bottom throughout the fermentation. Due to the rapid heat generating dynamics, temperature limitation remains a problem. This leads to axial temperature profiles with the highest temperature, sometimes over 10°C higher than the optimum temperature, occurring at the top of the bed. We present a model for the kinetics of microbial growth that incorporates the influence of the temperature variations that typically occur during solid-state fermentation in large-scale bioreactors. In this model, despite the fact that the growth rate depends on the current temperature of bioreactor through the specific growth rate constant that was expressed as a function of the temperature, it also depends on the time–temperature treatment that the organism has previously undergone through the rate of change in the level of the physiological factor, since the past temperatures affect the current value of physiological factor. Model predictions were compared to literature data for the growth of Aspergillus niger on wheat bran and agreed reasonably with experimental results. This approach to modeling has good potential for application in models of solid-state bioreactors. Also in this study, to investigate the temperature gradients in packed-bed bioreactors, two dynamic heat transfer models were considered and compared: (1) lumped dynamic heat transfer model, and (2) distributed dynamic heat transfer model. The predictions of distributed model have remarkably good agreement with experimental data rather than lumped model.

Solid-state fermentation; Packed-bed bioreactor; Growth kinetics; Heat transfer model