Surfactant solubilization, phenanthrene soil-aqueous systems

Understanding of surfactant sorption onto soil is needed to assess surbctant mobility in soil and surfactant-fecilitated transport of hydrophobic pollutants in soil/aqueous systems. Micelle-like amphiphilic nano-sized polyurethane (APU) particles synthaized from amphiphilic urethane acrylate anionomers could solubilize a model hydrophobic pollutant, phenanthrene wiliiin their hydrophobic interiors. Batch experiments were conducted with soil slurries to compare APU Sodium Dodecyl Sulfrde (SDS), anionic surfrictant for the sorption onto soil. APU particles (KniH).2 mUg) were weakly adsorbed onto the sandy soil compared to SDS (Ksui =l.3 mL/g), due to their chemically ciosslinked structure. Compared with SDS, APU particles exhibited the higher extraction efficiency to remove phenanthrene from the contaminated sandy soil. 

Surfactant Solubilization of Phenanthrene in Soil-Aqueous Systems and Its Effects on Biomineralization... 

A series of related experiments investigated nonionic surfactant sorption onto soil, mechanisms of nonionic surfactant solubilization of polycyclic aromatic hydrocarbon (PAH) compounds from soil, and microbial mineralization of phenanthrene in soil-aqueous systems with nonionic surfactants. Surfactant solubilization of PAH from soil at equilibrium can be characterized with a physicochemical model by using parameters obtained from independent tests in aqueous and soil-aqueous systems. The microbial degradation of phenanthrene in soil-aqueous systems is inhibited by addition of alkyl ethoxylate, alkylphenyl ethoxylate, or sorbitan- (Tween-) type nonionic surfactants at doses that result in micellar solubilization of phenanthrene from soil. Available data suggest that the inhibitory effect on phenanthrene biodegradation is reversible and not a specific, toxic effect. 

Figure 3 shows experimental data and model results for the nonionic micellar solubilization of phenanthrene in soil-aqueous systems with increasing dose of Triton X-100, C8PE95. Figure 4 shows experimental data and model results for solubilization of phenanthrene from soil with the alkyl ethox-ylate surfactant, Brij 30, C12E4. 

Phenanthrene Solubilization. A model characterizing the distribution of HOC in systems of soil and micellar nonionic surfactant solution was described previously (7). In this model HOC is assumed to partition among three distinct compartments the soil, the micellar pseudophase, and the aqueous pseudophase. The solubilization model accounts for the partitioning of HOC between the micellar pseudophase and the aqueous pseudophase, the increase in apparent HOC solubility associated with nonionic surfactant monomers in the aqueous pseudophase, the sorption of surfactant onto soil, and the increase in fractional organic carbon content of a soil as a result of surfactant sorption. Evaluation of the model with experimental data was described by Edwards et al. (12). 

Figure 4 showed the solubilization (i.e., mass fraction in liquid phase) of phenanthrene with the C12 E4 surfactant, Brij 30, in 1 8 (g of soihmL of water) soil-water systems. Phenanthrene solubilization in the soil-water system was observed only at a surfactant dose greater than about 0.0026 mol/L, about 0.1% (v/v), which is many times greater than the pure aqueous CAC value for C12E4 of 8.3 X 10 % (v/v). The surfactant doses reported in Figures 4 and 6 refer to the bulk addition of surfactant to water, and the liquid-phase surfactant concentrations are smaller than bulk surfactant doses because of surfactant sorption onto soil. 

The effective surfactant dose upon dilution was not inhibitory, and is less than the CMC in the soil-water systems. This dose to attain the CMC is nominally about 0.06% (v/v) or about 0.001 mol/L for Triton X-100 for a soil water ratio of 1 8 g/mL, as shown in Figure 3 for solubilization data or in reference 52 for surface-tension data. Therefore, the data in Figure 10 demonstrate recovery of phenanthrene biomineralization upon dilution of surfactant to sub-CMC aqueous-phase concentrations in soil-water systems. 

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