Aerobic Biodegradation of Vinasse by a Mixed Culture of Bacteria of the Genus Bacillus: Optimization of Temperature, pH and Oxygenation State

The aim of the study was to optimize the temperature, pH and oxygenation state for the aerobic biodegradation of vinasse using a mixed culture of thermo- and mesophilic bacteria of the genus Bacillus. At the initial stage of the study a series of experiments was performed in shake flasks over the temperature range of 30 to 65 degree C and an initial pH of the medium ranging between 5.40 (the pH of vinasse) and 9.5 in order to determine the optimal values of the two parameters (= 58 degree C, pH = 8.35) and thus maximize the extent of COD reduction (60.88%). At the subsequent stage, with the optimal values of temperature and initial pH, batch biodegradation processes were conducted in an STR with aeration at 1.0 vvm and two stirrer speeds, 550 rpm and 900 rpm, which provided a reduction in COD of 77.56% and 76.48%, respectively. With 900 rpm, a concomitant rise in the biodegradation rate was observed. The extent of COD reduction increased to 85.37% when biodegradation was conducted at 58oC (optimal temperature) and a stirrer speed of 900 rpm, the pH being maintained at 8.35 throughout the process.