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 2⁴⁻¹ 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) 2³. Responses of the emulsifying index after 24 h (EI₂₄) were first evaluated for fermentation in 250-mL flasks. Thus, the concentration of waste material that is able to provide EI₂₄ 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 EI₂₄ 100 % to toluene, 67 % to hexane, and 62 % to soybean oil), which can be suitable for applications in oil recovery was presented.