Enhanced biodegradation of persistent organic pollutants in industrial wastewaters by biosurfactants

ABSTRACT The release of specific industrial wastewaters, including nonbiodegradable and/or toxic pollutants, to receiving environments is today one of the most significant type of environmental pollution by hazardous wastes. Although biological treatment methods have been generally found most effective alternatives in the removal of persistent compounds, they require some enhancements due to the presence of refractory or toxic compounds in the wastewaters. For this reason, the use of surfactants in the removal of persistent organic pollutants by biological treatment was investigated as an enhancement technique for the biological treatment process. Surfactants, which are amphipathic molecules with both hydrophilic (water- soluble) and hydrophobic (water-insoluble) functional groups, act at the surface, or interface, between polar and nonpolar phases to modify the surface properties of both phases due to presence of the hydrophobic group. Surfactants reduce surface or interfacial tension and form colloidal sized aggregates called micelles. In contrast to synthetic surfactants, microbial surfactants (biosurfactants), which are a structurally diverse group of surfactants produced by various microorganisms under highly aerobic conditions, have several advantages over the synthetic counterparts such as biodegradability, low or no toxicity, acceptable production economics, and use in environmental control. The effectiveness of both synthetic and microbial surfactants in the remediation of contaminated soil and groundwater environments, oil spill remediation at sea and inland, and oil tank clean-up has been proven by many activities including researches, demonstrates and field-scale applications of in-situ surfactant enhancement as a technology. The application of surfactants can enhance soil and groundwater remediation in three ways:. by increasing contaminant mobility and solubility to improve the performances of conventional remediation technologies such as pump-and-treat;. by decreasing the mobility of contaminants to prevent their migration; and. to speed the rate of biodegradation of contaminants in soil. There are not any results about the use of surfactants in the removal of persistent organic pollutants in industrial wastewaters. The proven effectiveness of surfactants in soil and groundwater and oil spill remediation has been considered reasonable to expect that surfactants can also enhance the removal of persistent organic pollutants in industrial wastewaters. From this point of view, the effects of sophorolipid type biosurfactant on the removal of persistent organic pollutants in industrial wastewaters have been examined in this study. To determine the effectiveness of sophorolipids used in the experimental studies both synthetic wastewater samples, prepared by gasoline and kerosene, and real wastewater samples taken from a dye industry were used. Moreover, different sophorolipid concentrations (0 to 100 mg/L) were examined to optimize biosurfactant-enhanced degradation of persistent pollutants in industrial wastewaters. The results of this study indicate that the biodegradation of persistent organic pollutants in industrial wastewaters is enhanced by the use of biosurfactants. The principal mechanism that enhances the biodegradation is the increasing solubility of poorly soluble compounds in the wastewater. According to the results of this study, it can be expected that biosurfactant-enhanced degradation would result in faster and more complete degradation.