Kinetic and feasibility studies of ultrafiltration of viscous xanthan gum fermentation broth

Abstract

Ultrafiltration of xanthan gum solution as an alternative method to alcohol precipitation for xanthan gum recovery from dilute fermentation broth was studied. A polysulfone membrane hollow fiber (with 500 000 MWCO) tubular cartridge was used. The xanthan fermentation broth, which is highly viscous at its normal concentration of ∼2.5 (w/v)%, was concentrated to 13.5 (w/v)% or higher, with a recovery yield of ∼95% or higher. During ultrafiltration, the flux remained almost constant for xanthan concentrations up to ∼8%. It then decreased dramatically as the xanthan concentration increased beyond 8%. The decreased filtrate flux can be attributed to the decreased pumping (shear) rate and the increased viscosity that resulted at higher xanthan concentrations. When the xanthan concentration was held constant during ultrafiltration, the filtrate flux remained almost unchanged for the entire 2-h period studied, suggesting that the process was stable and no significant fouling occurred. In general, the filtrate flux 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 xanthan solution, but did not affect the filtration performance. Even under high-shear-rate conditions, ultrafiltration did not give any observed adverse effects on the rheological properties and molecular weight of the xanthan polymer. Thus, ultrafiltration can be used to concentrate xanthan broth from fermentation by a factor of five or higher, thereby reducing the amount of alcohol needed for xanthan recovery by at least 80%.