XANTHAN GUM PRODUCTION - AN UNSTRUCTURED KINETIC-MODEL

Xanthan production was studied in a stirred-tank fementor and modeled using unstructured kinetic models, First, the influences of the operat ional conditions have been studied. Temperature (between 22 and 34 deg rees C), aeration (changing stirrer speed between 150 and 1,000 rpm, m aintained at constant or varied through fermentation time), and the pH control (with two alkalis) were analyzed. Then, unstructured kinetic models proposed in the literature for this system were reviewed and ap plied. These models have been checked to describe the experimental res ults, calculating the parameters by nonlinear regression. The results show that these models do not take into account all the necessary nutr ients, which are carbon source, nitrogen source, and dissolved oxygen, Afterward, an unstructured kinetic model describing biomass, carbon s ource, nitrogen source, and dissolved oxygen evolutions was proposed a nd applied. Parameters estimation were carried our by means of both di fferential and integral methods. Parameters values were finally obtain ed applying an integral method using nonlinear regression techniques. The model proposed in this work is composed of five differential equat ions with production rates of the five components taken into account: biomass, carbon, and nitrogen sources, xanthan, and dissolved oxygen, capable of fitting all the three experiments considered, at different temperatures and controlling and not controlling pH.