XANTHAN PRODUCTION ON CRUDE GLYCEROL BY LAB-SCALE BIOREACTOR CULTIVATION OF LOCAL Xanthomonas ISOLATE

Abstract

Intensive development of the global biodiesel industry has led to the generation of a large excess of crude glycerol, which is impure, and its disposal into the environment is unacceptable without previous purification. Since purification costs are high, the application of crude glycerol in biotechnological production of value-added products represents a promising solution for a sustainable utilization of this effluent. The aim of this study was to examine xanthan biosynthesis by the Xanthomonas PL 3 strain on a medium containing crude glycerol from biodiesel production in a laboratory-scale bioreactor in order to further scale up this bioprocess. Xanthan was produced by submerged cultivation in a crude glycerol-based medium (glycerol content of 20 g/L) in a 3 L lab-scale bioreactor (working volume of 2 L), under aerobic conditions for 168 h (0-48 h: 25°C, 1 vvm and 200 rpm; 48-168 h: 30 °C, 2 vvm, and agitation rate adjusted according to the dissolved oxygen concentration which was maintained at values higher than 30%). The bioprocess was monitored by the analysis of cultivation medium samples in predetermined time intervals, and its success was estimated based on the xanthan concentration in the medium, separated biopolymer average molecular weight and degree of nutrient conversion. In the applied experimental conditions, 11.10 g/L of xanthan with the average molecular weight of 2.85·105 g/moL was biosynthesized. At the end of this bioprocess, the degree of total glycerol, nitrogen and phosphorous conversion was 62.82%, 41.54% and 24.80%, respectively. Results obtained in this study suggest that the Xanthomonas PL 3 strain has the ability to produce xanthan of good quality on cultivation media containing crude glycerol from the biodiesel industry.