Economic optimized medium for tensio-active agent production by Candida sphaerica UCP0995 and application in the removal of hydrophobic contaminant from sand

Abstract

Statistical experimental designs and response surface methodology were employed to optimize the concentrations of agroindustrial residues as soybean oil (SORR) from refinery, and corn steep liquor (CSL) from corn industry, for tensio-active agent produced by Candida sphaerica UCP 0995. Three 2(2) full factorial design were applied sequentially to investigate the effects of the concentrations and interactions of soybean oil refinery residue and corn steep liquor on the surface tension of free-cell culture broth for 144 h. Two 2(2) central composite designs and response surface methodology were adopted to derive a statistical model to measure the effect of SORR and CSL on the surface tension of the free-cell culture broth for 144 h. The regression equation obtained from the experimental data using a central composite design was solved, and by analyzing the response surface contour plots, the optimal concentrations of the constituents of the medium were determined: 8.63% v/v (≅9% v/v) of SORR and 8.80% v/v (≅9% v/v) CSL. The minimum surface tension predicted and experimentally confirmed was 25.25 mN/m. The new biosurfactant, denominated Lunasan, recovered 95% of motor oil adsorbed in a sand sample, thus showing great potential for use in bioremediation processes, especially in the petroleum industry.

Keywords: Candida sphaerica; central composite design; factorial design; optimization; tensio-active agent.

Figure 1.

First 2² full factorial design—Pareto’s Chart of standardized effects for (1) soybean oil refinery residue and (2) corn steep liquor using surface tension as response variable. The point at which the effect estimates were statistically significant (p = 0.050) is indicated by dashed line.

Figure 2.

Second 2² full factorial design—Pareto’s Chart of standardized effects for (1) soybean oil refinery residue and (2) corn steep liquor using surface tension as response variable. The point at which the effect estimates were statistically significant (p = 0.050) is indicated by dashed line.

Figure 3.

Third 2² full factorial design—Pareto’s Chart of standardized effects for (1) soybean oil refinery residue and (2) corn steep liquor using surface tension as response variable. The point at which the effect estimates were statistically significant (p = 0.050) is indicated by dashed line.

Figure 4.

Central composite design—Pareto’s Chart of standardized effects for (1) soybean oil refinery residue and (2) corn steep liquor using surface tension as response variable. The point at which the effect estimates were statistically significant (p = 0.050) is indicated by dashed line.

Figure 5.

Surface tension response surface showing interaction between soybean oil refinery residue and corn steep liquor concentrations.