Application of a Low Cost Biosurfactant in the Removal of Heavy Metals in Soil

Abstract

Several synthetic surfactants have been used in heavy metals decontamination tests in soils. However, the need of substitution of synthetic compounds by natural tensoactives has motivated researches for the use of surfactants of microbiological nature, the so-called biosurfactants. The use of biosurfactants in bioremediation processes has stood out due to the characteristics of these compounds as biodegradability, reduced toxicity and efficiency in the removal of heavy metals from soils and waters. Thus, a biosurfactant was produced by the yeast Candida guilliermondii UCP 0992 in medium formulated with distilled water supplemented with 4.0% corn steep liquor, 2.5% sugar cane molasses, and 2.5% residual soybean oil. The biosurfactant was initially characterized as an anionic molecule with capacity to reduce the surface tension of the water from 72.0 to 28.0 mN/m in the concentration of 0.42%, corresponding to its critical micelle concentration (CMC). The anionic biosurfactant showed no toxic effect on plant seeds of cabbage (Brassica oleracea) and was able to significantly reduce the electrical conductivity of solutions containing heavy metals, demonstrating the ability to complex metal cations, and then applied the removal of metals contained in soil samples from a battery industry. Solutions of the crude and isolated biosurfactant in different concentrations were tested in the mobilization of Iron, Zinc and lead metals contained in the soil. Solutions of HCl were also tested combined with the biosurfactant. The crude biosurfactant, that is, in its most economical form of application, was able to remove 98.9% of Zn, 89.3% of Fe and 89.1% of Pb. The properties of the biosurfactant as well as the results of the metal removal experiments clearly demonstrate the feasibility of applying this biomolecule as a biotechnological additive to remediation processes that consider the preservation and reduction of environmental impacts on ecosystems, essential aspects for the maintenance of life quality and social well- being.