Strategy for waste management in the production and application of biosurfactant through surface response methodology

This study aims to identify the optimal biosurfactant production process via fermentation by Bacillus subtilis , using waste material as alternative substrates (glycerin, water from potatoes processing, corn steep liquor, and frying oil), thereby highlighting the absence of synthetic substrates. A fractional factorial design 2 4−1 was previously used to determine the effects of the concentrations of the four substrates, selecting three of them to be used in a central composite rotatable design (CCRD) 2 3 . Responses of the emulsifying index after 24 h (EI 24 ) were first evaluated for fermentation in 250-mL flasks. Thus, the concentration of waste material that is able to provide EI 24 up to 100 % from 9 % of glycerin and 1 % of potato peel was determined, with subsequent experimental validation at the optimized point. One-liter-bench-batch fermentation with the optimum medium (based on the CCRD) was also carried out. In order to compare, another 1-L-bench-batch fermentation was performed using residual glycerin through the biosurfactant concentrations, dry weight, oxygen dissolved, and pH profile. Evidence of high potential for biosurfactant production (with EI 24 100 % to toluene, 67 % to hexane, and 62 % to soybean oil), which can be suitable for applications in oil recovery was presented.