Abstract: The specific DBT desulfurization bacterium Rhodopseudomonas sp. AS-21 was selected. The effects of temperature, pH, carbon source, nitrogen source, and initial concentration of DBT on S removal rate and cell concentration were investigated by single-factor experiments. The best conditions for the growth and desulfurization of AS-21 is 30℃, initial pH 7.5, concentration of glycerin as carbon source 10g/L, concentration of NH4Cl as nitrogen source 2g/L and initial concentration of DBT 100mg/L. The significance analysis results with Design-Expert show that temperature, pH and initial concentration of DBT have higher effects on desulfurization. Box-Behnken Design (BBD) response surface methodology was used to design total 20 experiments with three factors and three levels to obtain quadratic regression model for desulfurization rate and cell mass concentration. The optimization solution of the maximum response values under the simulated conditions by Design-Expert software predicts that the best factors for the highest desulfurization rate and strain growth are 29.70℃，pH 7.43，initial concentration of DBT 105.47mg/L. The highest desulfurization rate and strain growth are 72.32% and 2.311g/L, respectively, which are proven to be right through experiments.

Key words: biodesulfurization , dibenzothiophene, desulphurization condition, optimization