Production of Acetic Acid from Carbon Dioxide by Immobilized Acetobacterium woodi in Bubble-Column Bioceactor

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An anaerobic bacterium, Acetobacterium woodii, can produce acetic acid from CO_2. The utilization of such bacteria is of enormous value, not only for the development of C1 chemistry but also for the fixation of CO_2 in the atmosphere. The object of this study is to find the problems to be solved in the industrial application of A. woodii by using the bioreactors.We have developed a 300 ml bubble-column type bioreactor with the porous plate as gas distributor for the advantageous utilization of CO_2 by A. woodii (ATCC 29683). Basic growth characteristics and some optimal operational conditions for A. woodii (temperature, H_2/CO_2 ratio, medium et al.) were determined by using test tubes with reciprocal shaking. The production of acetic acid from H_2 and CO_2 by A. woodii was examined in the bubble-column bioreactor using two types of anaerobes, suspended and immobilized cells. In the immobilized-cell system, bacteria were entrapped in calcium arginate cell. Higher acetate productivity w … More as found in the culture of suspended cells.From the practical viewpoint, the establishment of a long-range continuous cultivation method of such bacteria will be required. One has to find a proper method of the separation of the cells from their media. Flocculation of bacteria will assist in the continuous high density cultivation using suspended cells in place of the immobilization methods for the cells. Flocculation of A. woodii by a variety of flocculants was tested to achieve high density cultivation using suspended cells of A. woodii for acetate production. Cationic synthetic polymeric flocculants having a strong positive charge were found to be highly effective to flocculate A. woodii. This approach was applied to the continuous production of acetic acid in the bubble-column bioreactor, and its usefulness was confirmed. This cultivation method is valuable not only for the simplification of the process, but also for the utilization of the energy required to the separation of the cells and the liquid contents. Less