KINETIC AND FEASIBILITY STUDIES OF ULTRAFILTRATION OF VISCOUS XANTHANGUM FERMENTATION BROTH

Ultrafiltration of xanthan gum solution as an alternative method to al cohol precipitation for xanthan gum recovery from dilute fermentation broth was studied. A polysulfone membrane hollow fiber (with 500 000 M WCO) tubular cartridge was used. The xanthan fermentation broth, which is highly viscous at its normal concentration of similar to 2.5 (w/v) %, was concentrated to 13.5 (w/v)% or higher, with a recovery yield of similar to 95% or higher. During ultrafiltration, the flux remained a lmost constant for xanthan concentrations up to similar to 8%. It than decreased dramatically as the xanthan concentration increased beyond 8%. The decreased filtrate flux can be attributed. to the decreased pu mping (shear) rate and the increased viscosity that resulted at higher xanthan concentrations. When the xanthan concentration was held const ant during ultrafiltration, the filtrate flux remained almost unchange d for the entire 2-h period studied, suggesting that the process was s table and no significant fouling occurred. In general, the filtrate fl ux decreased with increasing xanthan concentration and increased with increasing pumping (shear) rate and trans-membrane pressure difference . Changing the solution pH had a slight effect on the viscosity of xan than solution, but did not affect the filtration performance. Even und er high-shear-rate conditions, ultrafiltration did not give any observ ed adverse effects on the theological properties and molecular weight of the xanthan polymer. Thus, ultrafiltration can be used to concentra te xanthan broth from fermentation by a factor of five or higher, ther eby reducing the amount of alcohol needed for xanthan recovery by at l east 80%.