Characterization of concentration and purification parameters and operating conditions for the small-scale recovery of surfactin

Batch recovery including concentration and purification of surfactin from the cell-free fermentation broth was carried out using an ultrafiltration membrane in a magnetically stirred cell system. The filtration characteristics of surfactin on passing through the polymeric membrane, such as permeate flux, rejection coefficient, concentration factor, solute yield or purification factor and recovery factor were evaluated. The effects of the trans-membrane pressure, initial surfactin concentration and the pH of the surfactin solution on the permeate flux were also determined. A maximum of 166-fold concentration of surfactin was rapidly achieved under the optimum trans-membrane pressure and solution pH. The feed surfactin concentration of about 0.5 g L−1 resulted in the formation of a gel polarized layer which was difficult to remove by magnetic stirring, thereby decreasing the permeate flux and the solute yield. The present investigations also qualitatively compare the purity of the final product obtained through solvent extraction and ultrafiltration. The purity of surfactin obtained by ultrafiltration was found to be 70%, as calculated from critical micelle concentration value (CMC) of 0.017 g L−1 against that of 0.013 g L−1 for surfactin (Sigma, 98% pure), used as the reference standard. Thus, an understanding of ultrafiltration characteristics and operating conditions from the analyses of the present study constitutes a very important milestone for process optimization and scale-up.