Production and Application of No-purified Rhamnolipids in the Soil-washing of TPHs Contaminated Soils

Aims: This work aimed to demonstrate the feasibility of producing (mono- and di-) rhamnolipids employing a strain of Pseudomonas aeruginosa strain ATCC 9027 employing olive oil as a substrate and some mineral salts. This rhamnolipid is a biosurfactants with multiple applications The CMC of this product under different conditions (filtered, unfiltered, in the presence and absence of Fe and Mg, at different pH values) was assessed. At the end, the UP was assessed in the washing of a TPH contaminated soil.

Place and Duration of Study: Bioprocess department. Unidad Profesional Interdisciplinaria de Biotecnologia-IPN facilities, during 2016.

Methodology: Rhamnolipids were produced with P. aeruginosa in olive oil, then by drying the culture broth was generated an unpurified product (UP) that contained 0.19% rhamnolipids. Critical micelle concentration CMC of UP products were evaluated in the presence of Ca2+ or Fe3+ from 0.5 to 2 mM, and pH values from 4 to 10. Finally, this surfactant was assessed in the washing of hydrocarbon-contaminated soils, and compared with other synthetic surfactants.

Results: It was found that CMCs were similar to those reported in the literature for pure rhamnolipids. The UP products have shown dynamic behavior in the soil washing at concentrations below 176 mg/L because removed 80% of 6,500 mg TPH/Kg from a gravel-sandy soil; the rhamnolipids could be removed TPH through mobilization mechanism.

Conclusion: It was possible to produce rhamnolipid using olive oil as carbon source and strain of P. aeruginosa ATCC 9027 to levels of 100 mg/L. It was feasible to produce a powder containing 1.19% of rhamnolipids. The UP had better properties as a surfactant than the purified product. The pH affects the CMC of the rhamnolipids in a way that promotes their behavior as ionic surfactant or nonionic surfactant. The ionic strength with Ca 2+ and Fe3+ has an effect on the CMC of rhamnolipids so that the decreases in the range of 35 to 41 mg/L in the presence of 0.5 to 2 mM of metals. The UP rhamnolipids were employed for washing soil contaminated with 6,500 mg/kg increased TPH removal at low concentrations and to be as effective as chemical surfactants. TPH removal observed was about 80% for rhamnolipid with a CMC x 0.074 concentration.