The Design and Construction of a Power Compensation Heat Flow Calorimeter For The Study of Fermentation Processes.

The evolution or absorption of heat is the most fundamental indicator of chemical reactions; this phenomenon has been used for decades within the chemical process industries to both quantify and optimise chemical processes. Only recently however, has it become accepted that heat evolution data can be used both as an on-line process dependent variable and as an analytical method for optimising fermentation processes. As heat evolution/absorption is a fundamental by-product of all metabolic processes it can be used to gauge all types of fermentations, both aerobic and anaerobic. In addition heat evolution can be used to determine not only the number of cells but also the state of the cells present within any given fermentation. Therefore a cheap calorimeter designed solely for use within the fermentation industry could prove to be an important analytical tool in the optimisation of bio-processes. A macro-scale calorimeter has been designed with this purpose in mind. The unit operates on the power compensation principle and has been designed to be cheap to build, easy to operate and both accurate and sensitive enough for fermentation process analysis. The calorimeter has a maximum heat detection limit of 10 watts with a sensitivity of 0.05 watts for aqueous systems and accuracy of +0.025 watts, with a maximum working volume of 0.8 dm* The calorimeter has been used to study the batch fermentation of Bacillus thuringiensis; heat evolution has been detected and shown to correlate both with the number of cells present, and the state of the cells within the fermentation. Specific stages within the fermentation have been identified solely by the rate of heat evolution, these stages are not detectable using any other single monitoring technique, showing the instrument's suitability for the study of fermentation processes. The results from the developed instrument have been compared with those obtained from the "state of the art" heat flow calorimeter under identical conditions. Excellent correlations between the two instruments have been generated showing the new calorimeters' suitability for heat evolution studies. A technique has been developed by which any large-scale reactor can be modified easily to generate thermometric data that can be used either as an on-line process variable or be used in reaction analysis and evaluation. The thermometric data generated by the modified pilot scale fermenter has been compared with that generated by both the developed calorimeter and a "state of the art" calorimeter". Excellent correlations have been determined between all three calorimetric systems for the batch cultivation of Bacillus thuringiensis under near identical fermentation conditions. The usefulness of heat evolution rates as a method of both on line process monitoring and as an analytical method in process optimisation has been shown.