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Xanthan gum production was studied using sugarcane broth as the raw material and batch fermentation by Xanthomonas campestris pv. campestris NRRL B-1459. The purpose of this study was to optimize the variables of sucrose, yeast extract, and ammonium nitrate concentrations and to determine the kinetic parameters of this bioreaction under optimized conditions. The effects of yeast extract and ammonium nitrate concentrations for a given sucrose concentration (12.1-37.8 g L(-1)) were evaluated by central composite design to maximize the conversion efficiency. In a bioreactor, the maximum conversion efficiency was achieved using 27.0 g L(-1) sucrose, 2.7 g L(-1) yeast extract, and 0.9 g L(-1) NH(4)NO(3). This point was assayed in a shaker and in a bioreactor to compare bioreaction parameters. These parameters were estimated by the unstructured kinetic model of Weiss and Ollis (Biotechnol Bioeng 22:859-873, 1980) to determinate the yields (Y (P/S)), the maximum growth specific rate (mu (max)), and the saturation cellular concentration (X*). The parameters of the model (mu (max), X*, m, lambda, alpha, and beta) were obtained by nonlinear regression. For production of xanthan gum in a shaker, the values of mu (max) and Y (P/S) obtained were 0.119 h(-1) and 0.34 g g(-1), respectively, while in a bioreactor, they were 0.411 h(-1) and 0.63 g g(-1), respectively.

In order to optimize and evaluate the influence of nitrogen, phosphorus, and inoculum concentrations on the biodegradation of hydrocarbon contaminated effluents, experiments based on central composite design (CCD) method were carried out for 3 days, employing C1 mixed culture and intermittent aeration. The independent variables were nitrogen concentration (X 1 ), phosphorus concentration (X 2 ), and inoculum concentration (X 3 ) and the removal of total petroleum hydrocarbons (TPH) was the dependent variable. The optimized nutrients ratio (C:N:P = 100:20:2.7) and inoculum concentration (1.32 g/ l) provided TPH removal of 71.8% after processing for three days. Analysis using gas chromatography identified five hydrocarbons classes: paraffins, isoparaffins, olefins, naphthenics, and aromatics. The naphthenic compounds did not degrade as readily as the other hydrocarbons that were identified. The following degradation percentages were obtained: 87.1% for the paraffins, 77.7% for the isoparaffins, 78.6% for the olefins, 38.4% for the naphthenics, and 71.7% for the aromatics.

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