Optimization of low-cost biosurfactant production from agricultural residues through response surface methodology.

Biosurfactants are surface-active compounds capable of reducing surface tension and interfacial tension. Biosurfactants are produced by various microorganisms. They are promising replacements for chemical surfactants because of biodegradability, nontoxicity, and their ability to be produced from renewable sources. However, a major obstacle in producing biosurfactants at the industrial level is the lack of cost-effectiveness. In the present study, by using corn steep liquor (CSL) as a low-cost agricultural waste, not only is the production cost reduced but a higher production yield is also achieved. Moreover, a response surface methodology (RSM) approach through the Box-Behnken method was applied to optimize the biosurfactant production level. The results found that biosurfactant production was improved around 2.3 times at optimum condition when the CSL was at a concentration of 1.88 mL/L and yeast extract was reduced to 25 times less than what was used in a basic soybean oil medium (SOM). The predicted and experimental values of responses were in reasonable agreement with each other (Pred-R(2) = 0.86 and adj-R(2) = 0.94). Optimization led to a drop in raw material price per unit of biosurfactant from $47 to $12/kg. Moreover, the biosurfactant product at a concentration of 84 mg/L could lower the surface tension of twice-distilled water from 72 mN/m to less than 28 mN/m and emulsify an equal volume of kerosene by an emulsification index of (E24) 68% in a two-phase mixture. These capabilities made these biosurfactants applicable in microbial enhanced oil recovery (MEOR), hydrocarbon remediation, and all other petroleum industry surfactant applications.