Determination of the heat of some aerobic fermentations

An accurate technique has been developed and applied to continuous measuring of the rate of heat production during a fermentation process. A special temperature control system was developed and used to monitor the heat quantity. The results were corrected for heat losses and gains based on the overall heat balance on the fermentor. The technique was used for precisely determining the rate of heat evolution of Aspergillus niger, Escherichia coli, Candida Upolytica, Candida intermedia and Candida utilis grown on etlianol and different carbohydrate and hydrocarbon sources. Based on the experimental data, a correlation between the rate of heat released and the rate of oxygen consumed has been determined as Q_term = 0.465 MJ/mol O₂ · Δ0₂. The total heat released also correlated well with the total oxygen consumed by the growing culture. The proportionality constant for this correlation was 0.461 MJ/mol O₂. The experimental results agreed well with the theoretical predictions and with those developed by the dynamic calorimetric technique. The derived correlations reported in this study arc useful for fermentation process design, optimization and control as well as indicators of microbial metabolic activity.