Utilisation of winery wastewater for xanthan production in stirred tank bioreactor: Bioprocess modelling and optimisation

Abstract In this study, the xanthan biosynthesis by Xanthomonas campestris ATCC 13951 is presented as a sustainable solution for winery wastewater utilisation. To improve examined biotechnological process, optimisation of temperature, aeration rate and agitation speed for xanthan production in stirred tank bioreactor was carried out. Experimental design methodology and statistical approaches were used to define mathematical models which describe the individual and interactive effects of varied parameters on the xanthan biosynthesis and to optimise their values. The optimal conditions for the most profitable xanthan production on winery wastewater based medium with 30 g/L sugar were found to be temperature of 29.34 °C, air flow rate of 1.95 vvm and agitation speed of 475.50 rpm. Performing bioprocess under these conditions resulted in accumulation of large quantity of good-quality xanthan (23.85 g/L) and achievement of significant purification levels of winery effluents which is confirmed by high values of sugar, nitrogen and phosphorus conversion (90.79%, 71.74% and 83.14%, respectively). The present study provides valuable information about efficacy of winery wastewater utilisation under different operational conditions that can be used for bioprocess scale up and design of bioreactors with appropriate constructional characteristics, which is a prerequisite of the industrialization of examined bioprocess.