PROPIONIC AND ACETIC ACIDS FERMENTATION USING PROPIONIBACTERIUM ACIDI-PROPIONICI IN BATCH AND CONTINUOUS CULTURE

The purpose of this study was to increase the rate of production of propionic and acetic acids by fermentation by increasing the reaction rate and reducing the fermentation time. The fermentation of mixed glucose and xylose solutions were carried out using Propionibacterium acidi-propionici in batch and continuous culture. Optimum fermentation conditions of pH, sugar concentration and nutrient additions were obtained in batch culture. The optimum sugar concentration was obtained in batch fermentation for an equal distribution of glucose and xylose at a concentration level of 15 g/L. The optimum pH level for organism growth, sugar conversion and organic acid fermentation was found to be around 7.1. A ninety five percent conversion of glucose and xylose was obtained after 12 days of batch fermentation.;Propionibacterium acidi-propionici was immobilized with glutaraldehyde on Raschig rings in a packed bed reactor. The use of the immobilized cell reactor reduced the long reaction time (12 days) in the batch reactor to a retention time of 1 day. High production rates of organic acids were achieved, yielding about 19 g and 4 g per liter of acetic and propionic acids, respectively. An 86 percent conversion of glucose was obtained for an 8 hour retention time. The fermentation of high sugar concentrations (10 percent total sugar) in the immobilized cell reactor resulted in a 54 percent conversion of glucose. The immobilized reactor is about 5 - 8 times faster and about 4 times more productive than the continuous stirred tank reactor.;When a Continuous-Stirred-Tank Reactor was operated at the optimum pH and sugar concentration, more than 90 percent conversion of glucose and 86 percent conversion of xylose were achieved at a 72 hour retention time. Ninety-three percent conversion of hydrolyzate sugar was obtained in continuous culture fermentation.