Indirect measurement of water content in an aseptic solid substrate cultivation pilot‐scale bioreactor

Abstract

A lack of models and sensors for describing and monitoring large-scale solid substrate cultivation (SSC) bioreactors has hampered industrial development and application of this type of process. This study presents an indirect dynamic measurement model for a 200-kg-capacity fixed-bed SSC bioreactor under periodic agitation. Growth of the filamentous fungus Gibberella fujikuroi on wheat bran was used as a case study. Real data were preprocessed using previously reported methodology. The model uses CO2 production rate and inlet air conditions to estimate average bed water content and average bed temperature. The model adequately reproduces the evolution of the average bed water content and can therefore be used as an on-line estimator in pilot-scale SSC bioreactors. To obtain a reasonable fit of the bed temperature, however, inlet air humidity measurements will have to be adjusted with a data reconciliation algorithm. Good estimation of temperature is important for the future design of improved water content estimation using state observers. The model also provides insight into understanding the complex behavior of the dynamic system, which could prove useful when establishing advanced model-based operational and control strategies.

Recent developments in modeling of solid-state fermentation: heat and mass transfer in bioreactors

“…In experiments conducted with a 200 kg capacity pilot scale bioreactor significant deviations occurred between the measured and predicted temperatures, these deviations being attributed to measurement errors. On the other hand, predicted bed water contents agreed closely with values measured off-line, indicating that the model can be a useful softsensor for use in control of bioreactor water content [29].…”

“…The contribution of the bioreactor wall to heat accumulation is typically neglected in bioreactor models [1], but can be significant in large-scale bioreactors [29]. The parameter k exp is an empirical parameter that was necessary to account for errors introduced by the assumption of bed homogeneity, which was not achieved in practice.…”

“…Pena y Lillo et al [29] used a model that assumed perfect mixing in order to use indirect on-line measurements to estimate the water content of the substrate bed. This allows water content to be used as the control variable even though on-line measurement of water content itself is not possible.…”

Bed moisture estimation by monitoring of air stream temperature rise in packed-bed solid-state fermentation

“…Most of the early models have no practical significance as they either neglected evaporation or assumed continuous and uniform water addition. Only a few models have considered comprehensive balances (Pena y Lillo et al, 2001). Most of the models have been developed as tools for guiding bioreactor design; the prerequisite of such models is an accurate growth kinetic formulation, in which it is necessary to describe the dependence of growth on the bed temperature and moisture content.…”

“…The solution is to use indirect estimation methods, sometimes referred to as 'soft-sensors'. These methods are based on the measurement of gas stream variables that can be monitored online and the use of mathematical models to convert these measurements into estimates of bed moisture content (Pena y Lillo et al, 2001).…”