Solubilization And Bioavailability Enhancements Of Polycyclic Aromatic Hydrocabon (PAHs) By Surface Active Substances

Due to the characteristics of PAHs such as the low bioavailability, low solubility and strong sorption, the secondary contamination often occurred in the soil matrix if the remediation approach used the solubility-enhanced chemical surfactants that usually are non-biodegradable. In this paper, biosurfactants - humic acid and Saponin were chosen as the surfactants to be used in the flushing alternative of soils that were contaminated by hydrophobic and insoluble PAHs, and their effects on solubility-enhancement and reaction mechanisms were studied. In the comparision of solubilizing and washing efficiency by using the chemical synthetic surfactants - humic acid and Saponin, the solubilization of PAHs mixed with Saponin and nonionic surfactants were investigated focusing on the co-enhancement of solubility and reduction in partition of nonionic surfactants into organic phases. At last, biodegradation of anthracene in humic acid and Saponin solutions were determined and compared with chemical synthetic surfactant Tween80. The objectives of the present studies are to find the new, safe, economical and high-efficiency novel agents that can be used in the PAHs contaminated soils while the essential theory for the application are summarized.Chapter 1. Study on surfactant-enhanced remediation of soil and groundwater contaminated by Polycyclic aromatic hydrocarbonsPolycyclic aromatic hydrocarbons(PAHs) have been of a great interest in recent years because of their carcinogenic and mutagenic potential .A review on the source ,the kind ,the distribution and the property of PAHs was presented. And the mechanism of chemical,biological and chemical-biological remediations of organic contaminated soil and groundwater was introduced. Meanwhile the paper reviews the researchs on surfactants applied in the PAHs remediation in recent years and the prospects on this field are discussed.Chapter 2. Water Solubility Enhancement of anthracene and phenanthrene by biosurfactant -SaponinThe solubilizations of anthracene and phenanthrene were characterized, by using Saponin, and compared with three typical chemical surfactants (Brij35, TX100, SDS) in water solution and PAH-polluted soil. The results showed that a solubilization of anthracene and phenanthrene were dramatically enhance when dosages of surfactants were over their respective critical micelle concentration (CMC), and their solubilization capabilities were as follows Brij35>Saponin>TX100. Furthermore, anthracene and phenanthrene were synergistically solubilized by mixed Saponin -nonionic surfactant solutions. It was indicated that the mixed Saponin and surfactants were attributed to the increase of partition coefficient ( Kmc) of solutes between micelle and aqueous phase. The efficiencies of synergistic solubilization were up to 19.97-87.19%. The desorption ratios of anthracene and phenanthrene in the soil were increased with the increase of Saponin and surfactant concentrations. Chapter 3. Water Solubility Enhancement of PAHs by using humic acidThe solubilization of anthracene was characterized by using humic acid in comparison with three typical nonionic surfactants (Tween20,Tween80,TX100). The influences of inorganic salts and organic cosolutes on solubilization behavior were also investigated. The results showed that not only surfactants in the range of concentration above critical micellar concentration (CMC) but also humic acid could greatly enhance the solubilization of anthracene, and its solubility had the linear relationship with the concentration of surfactants or humic asid. The solubilization capabilities were as follows HA>Tween20>Tween80>TX100. The work presented here demonstrated that the natural HA could be an attractive alternative to synthetic surfactants in ex situ washings for PAH-polluted soils due to its additional capacity.Chapter 4. Solubilization thermodynamics and kinetics of anthracene in the presence of Humic AcidThe solubilization thermodynamics and kinetics of hydrophobic pollutants anthracene in the humic acid micellar solutions have been examined using batch tests. The results showed that the solubilization rate of athracene was significantly enhanced with increasing temperature. The solubilization process of athracene was spontaneous, exothermic and entropy increasing withΔG^θ= -13.63 KJ. mol^-1,ΔH^θ=11.96 J.mol^-1,ΔS^θ= 45.78 J/K, as well asΔG^θ= -14.09 and -14.55 KJ. mol^-1 in 35℃and 45℃, respectively. A Elovich kinetics model fitted the solubilization data of anthracene well.Chapter 5. Effect of Saponin and Humic acid on Biodegradation of AnthraceneThe influences of Saponin (biosurfactant) and humic acid (surfactant-like substance) on the biodegradation of anthracene were studied in comparison with Tween80 (chemical surfactant).. The results indicated that it must take about 7d for microorganisms to produce the sufficient glycolipids to solubilize anthracene and made anthracene biodegradable in the absence of any surfactants. Saponin humic acid and Tween80 could be used to accelerate significantly biodegradation of anthracene, especially, Saponin and humic acid could dramatically shortened the onset time for biodegradation of anthracene, and the biodegradation rate could reach 98.2% and 98.4% within 2～4d, respectively. It was also discovered that the biodegradation of anthracene was affected by the concentrations of humic acid added and initial concentrations of anthracene.