• biosurfactant;
  • response surface methodology (RSM);
  • Bacillus subtilis;
  • fermentation conditions;
  • optimization

The aim of the study was to increase the production of biosurfactant by using the inexpensive medium materials and the optimized fermentation conditions. Five biosurfactant producers were isolated from oilfield wastewater. The most efficient strain S2 was identified through 16S rDNA sequence analysis, which exhibitted the highest similarities to Bacillus subtilis strains CCTCC M201162. The optimal medium composition of this strain were beer wastewater 40 g/L, diammonium phosphate (NH4H2PO4) 4 g/L, MgSO4 0.02 g/L, NaCl 5 g/L. The emulsification index (E24) was optimized using a box-behnken experimental design and response surface methodology(RSM). The RSM revealed that when pH was 7.2, temperature was 42.1°C, inoculum concentration was 5.2% (v/v) and rotate speed was 163 r/min, the optimal condition was obtained. Under this condition, the optimal E24 of the biosurfactant produced by Bacillus subtilis strains CCTCC M201162 was 81.20%, the production of crude biosurfactant increased from 0.72 g/L to 1.26 g/L and the surface tension of fermentation broth reduced from 72.0 mN/m to 22.8 mN/m. A quadratic response model was constructed through RSM designs, leading to a 75.0% increase of biosurfactant production by Bacillus subtilis strains CCTCC M201162. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 548–554, 2015