Environmental pollution by organic contaminants is a major problem today because it has affected many environments. Hydrophobic contaminants are of special concern since their molecules can be bound to the soil particles, but because of its low solubility in water and high interfacial tension, those contaminants cannot be easily removed. To help with desorption of contaminants, surfactants can be used in soil and water remediation technologies. Amphiphiles that can form micelles are termed as surface active agents or surfactants and are among the most commonly used chemicals in everyday life. Chemically produced surfactants have increasingly been replaced by biotechnology-based products, obtained either by enzymatic or microbial synthesis, because they can be produced using natural resources. The group of surface active biomolecules produced by living organism is called biosurfactants. Originally, biosurfactants attracted attention as hydrocarbon-dissolving agents in the late 1960s and as potential replacements for synthetic surfactants (carboxylates, sulfonates and sulfate acid esters) in the food, pharmaceutical, and oil industries. Synthetic surfactants currently used are usually toxic and hardly degraded and as such are also a contaminant in the environment. To replace synthetic surfactants, biosurfactant production needs to be cost-effective; therefore, it is important to develop culture conditions with low-cost materials using efficient biosurfactant-producing microbial strains. Although bacteria have been extensively studied for biosurfactant production, yeasts are also potential biosurfactant-producing microorganisms. Because of their unique structures, biosurfactants may have a greater range of properties that can be exploited commercially. This review article will describe microorganisms related to biosurfactant production, including yeasts, as well as their role in bioremediation.
Part of the book: Advances in Bioremediation of Wastewater and Polluted Soil
In order to evaluate the degradation of fuel oil no. 6 (FO6) in contaminated soil, laboratory-scale bioreactors were set up to study biostimulation, bioaugmentation, and natural attenuation processes. A solution of fertilizers was added in biostimulation and biouagmentation (0.03% N, 0.01% P). To the bioaugmentation process, an enrichment culture of indigenous hydrocarbon-degrading microorganisms was also added once a week. Total aerobic and hydrocarbon-degrading microorganisms were determined by plate count, and total petroleum hydrocarbon (TPH) concentration was determined gravimetrically (EPA method 9071b) every 15 days. After 1 year of study, degradation rate was higher for biostimulation (0.19 g TPH/day), followed by natural attenuation (0.18 g TPH/day) and bioaugmentation (0.16 g TPH/day). TPH showed a change in composition of hydrocarbons, attributed to microbiological activity. Microbial counts of hydrocarbon-degrading microorganisms were on the range of 4–6 log CFU/g soil. Preliminary bacterial identification corresponded to Pseudomonas, Rhodococcus, Actinomyces, and Bacillus strains; randomly amplified polymorphic DNA (RAPD); and denaturing gradient gel electrophoresis (DGGE) analysis demonstrated a large microbial diversity. From the degradation rates, it can be predicted that such limits will be achieved by increasing further 107–117 days of the treatments. Results demonstrated to be efficient on the restoration of contaminated soil, being an alternative to treat soils contaminated with heavy hydrocarbons.
Part of the book: Advances in Bioremediation and Phytoremediation