Solubilization And Bioavailability Enhancements Of Hydrophobic Organic Compounds By Surface Active Agents

Surfactant-enhanced remediation (SER) is one of the most efficient, the least time-consuming and a promising technique among the remedy approaches for the contaminated soil and groundwater. In the present dissertation, much reviewing was made on the principles, the current research results and the main problems of surfactant-enhanced remediation (SER). It was pointed out that an improved strategy for SER is to reduce the concentration of surfactant, the expenditure of technique and risk on ecosystem while the efficiency of surfactant utilization was maintained. Accordingly, microemuision and mixed anionic-nonionic surfactant were chosen as the alternatives due to their distinctive characteristics, respectively. The solubilizations of some hydrophobic organic compounds by microemulsions, together with mechanisms were studied. The comparison of solubilizing and washing efficiency of hydrophobic organic compounds by sodium castor oil sulfate (SCOS) microemuision with those by the synthetic surfactants were made. The solubilization of dense nonaqueous phase liquids (DNAPLs) by mixed surfactants was investigated in detail and the mechanisms of solubility enhancements and reduction in partitioning of nonionic surfactant into organic phases were presented. At last, biodegradation of phenanthrene in mixed surfactant solutions was tested and compared with that in single ones. The objectives of the present dissertation are to prospect novel agents and approaches for SER. The main original conclusions are drawn as following parts.(1) The solubilization of DNAPLs by mixed anionic-nonionic surfactant was studied. It was found that the partitioning of nonionic surfactant largely decreased using anionic one. The solubilization extents by mixed surfactant were much larger than that by single nonionic one when the initial dosages of surfactants were the same. Furthermore, mixed surfactant resulted in higher solubilities of DNAPLs in aqueous phase than single anionic one did. For example, solubilization efficiency for trichloroetnene by 10 g/L of 1:3 TX100-SDBS was 7.9 and 1.6 times as those by single TX100 and SDBS respectively. The high solubilizing efficiency by mixed surfactant was attributed to its large solubilization capacity and reduction in partitioning of nonionic surfactant. The reduction in partitioning was mainly due to the mixing micellization between anionic and nonionic surfactant. The theoretical measurement of the free energy of standard micellization was presented and the results showed the mixed micelles were more thermodynamically stable than single nonionic one.(2) It was found that the solubilization capacity of microemuision was larger than surfactant solution but the partition coefficients of organic solutes between microemulsified droplet (swollen micelle) and the aqueous phase, were equivalent tothose between micelle phase and the aqueous phase. The structure of SCOS emulsified droplet and the partitioning for solute was invariable throughout its concentrations. The solubilization and washing efficiency of hydrophobic organic compounds by SCOS microemulsion were high than those by the synthetic surfactants. The results showed that SCOS could be an alternative agent for surfactant in the application of remediation.(3) The biodegradation of phenanthrene in the mixed anionic-nonionic surfactant solutions was investigated. The results showed that the efficiency of solubilization was enhanced through mixing anionic surfactant with nonionic one and no inhibition was found in bidegradation of phenanthrene solubilized in mixed surfactant solutions while the biodegradation of phenanthrene was inhibited in single anionic surfactant solution. The rates of degradation in mixed surfactant solutions were the essential same as those in single ones, which indicated the mixed surfactant could enhance the bioremediation efficiency for polycyclic aromatic hydrocarbons.