Development of a large‐scale biocalorimeter to monitor and control bioprocesses

Abstract

Calorimetry has shown real potential at bench-scale for chemical and biochemical processes. The aim of this work was therefore to scale-up the system by adaptation of a standard commercially available 300-L pilot-scale bioreactor. To achieve this, all heat flows entering or leaving the bioreactor were identified and the necessary instrumentation implemented to enable on-line monitoring and dynamic heat balance estimation. Providing that the signals are sufficiently precise, such a heat balance would enable calculation of the heat released or taken up during an operational (bio)process. Two electrical Wattmeters were developed, the first for determination of the power consumption by the stirrer motor and the second for determination of the power released by an internal calibration heater. Experiments were designed to optimize the temperature controller of the bioreactor such that it was sufficiently rapid so as to enable the heat accumulation terms to be neglected. Further calibration experiments were designed to correlate the measured stirring power to frictional heat losses of the stirrer into the reaction mass. This allows the quantitative measurement of all background heat flows and the on-line quantitative calculation of the (bio)process power. Three test fermentations were then performed with B. sphaericus 1593M, a spore-forming bacterium pathogenic to mosquitoes. A first batch culture was performed on a complex medium, to enable optimization of the calorimeter system. A second batch culture, on defined medium containing three carbon sources, was used to show the fast, accurate response of the heat signal and the ability to perfectly monitor the different growth phases associated with growth on mixed substrates, in particular when carbon sources became depleted. A maximum heat output of 1100 W was measured at the end of the log-phase. A fed-batch culture on the same defined medium was then carried out with the feed rate controlled as a function of the calorimeter signal. A maximum heat output of 2250 W was measured at the end of the first log-phase. This work demonstrates that real-time quantitative calorimetry is not only possible at pilot-scale, but could be readily applied at even larger scales. The technique requires simple, readily available devices for determination of the few necessary heat flows, making it a robust, cost-effective technique for process development and routine monitoring and control of production processes.

Biothermodynamics of live cells: a tool for biotechnology and biochemical engineering

“…Yet heat effects in cellular cultures often go unnoticed when one is working with conventional laboratory equipment because most of the heat released by the culture is lost to the environment too quickly to give rise to a perceivable temperature increase. This, however, is completely different in microbial cultures at large scale [5][6][7][8]. As opposed to laboratory reactors, industrial-size fermenters operate nearly adiabatically due to their much smaller surface-to-volume ratio.…”

“…If the temperature increase in the cooling water, its flow rate, and the other relevant energy exchange terms such as agitation and evaporation rates were measured systematically, the heat dissipation rate of the cellular culture could quantitatively be monitored on-line in industrial fermenters. The information contained in this signal could, in principle, be used together with other on-line data in order to optimize the bioprocess and for on-line process control [8]. …”

“…Such measurements therefore provide a simple way to monitor the biological activity of a culture and thus to control the bioprocess. This approach has been demonstrated on a 300 l pilot-scale bioreactor producing biological pesticides in India by Voisard et al [8]. Later Türker [7] applied the method to a 100 m 3 industrial bioreactor.…”

The Application of Dielectric Spectroscopy and Biocalorimetry for the Monitoring of Biomass in Immobilized Mammalian Cell Cultures

“…Although no apparent change in the analysed substrates and products to biomass yields was observed, after day 10, the growth rate fell to 0.29 day Additionally, this study is a stepping stone towards using continuous heat flow rate measurements to evaluate in real-time cell activity at industrial scale. This work involved growing cells in a working volume of 1.4 L. At this scale, the surface area to volume ratio is high, consequently, the heat losses to the environment are significantly [31,45]. However, large reactors e.g., 12.5 m 3 have a much lower surface area to volume ratio, meaning that the heat loss is much smaller.…”

“…At small scale, heat production is difficult to measure as most of the heat is lost to the environment. This heat loss is explained by the high surface to volume ratio of the reactor [29,31]. However, at industrial scale, or at volumes of a few cubic meters, the surface to volume ratio is less significant, and may necessitate cooling instead [32,33].…”