Xanthan production in bubble column and air‐lift reactors

Abstract

A bubble column (0.05 m(3)) and an air-lift fermentor (1.2 m(3)) were used for the production of the exocellular microbial polysaccharide xanthan with Xanthomonas campestris in a synthetic medium. Upon oxygen depletion in the liquid, the xanthan production rate dropped sharply and then became a linear function of the oxygen transfer rate. The volumetric mass transfer coefficients for oxygen conformed to the correlation of Suh et al. Using this correlation in combination with the model for xanthan batch fermentation suggested by Peters et al., the xanthan fermentations in the bubble column were well described. The model also correctly predicted the time course of the molecular weight of the polysaccharide even when a complex medium was used. In the air-lift fermentor, however, the xanthan production rate and the xanthan yields with respect to oxygen and glucose were lower than expected at the overall oxygen transfer rate. The poor performance of the air lift was traced back to the lack of any oxygen supply in the downcorner.

The pyruvate content of xanthan polysaccharide produced under oxygen limitation

“…Although the trend is clear, the data basis may not suffice for a quantitative correlation. Xanthan produced in a complex medium at a gas velocity of 0.164 m/s (Suh et al, 1992) had a pyruvate content of 4.3 wt% which compares rather well with the result for the synthetic medium in Fig. 1.…”

Agitator speed and dissolved oxygen effects in Xanthan fermentations

“…There is gathering evidence that the specific Xanthan production rate is directly related to the specific oxygen uptake rate (Amanullah et al, 1997;Herbst et al, 1992;Peters et al, 1989b;Suh et al, 1990Suh et al, , 1992, which in turn is linked to agitation conditions that determine the total amount of cells participating in the fermentation and the DOT experienced by them. Flores et al (1994) conducted Xanthan fermenta- Figure 8.…”

Effects of rheological change by addition of carboxymethylcellulose in culture media of an air-lift fermentor on poly-D-3-hydroxybutyric acid productivity in autotrophic culture of hydrogen-oxidizing bacterium, Alcaligenes eutrophus

“…In recent years, air-lift fermentors have often been used for production of penicillin (Möller et al, 1992), ␣-amylase (Chevalier and de la Noüe, 1988), xanthan (Suh et al, 1992), and single cell protein (Westlake, 1986), instead of the traditional stirred-tank fermentor. Because the air-lift fermentor does not require mechanical agitation, the energy consumption is lower than that of a stirred-tank fermentor.…”