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. 

When nonionic surfactant is applied to a soil-aqueous system, the surfactant can exist as dissolved monomers, sorbed molecules on the soil, or aggregated groups of molecules called micelles. Molecules of HOCs in such a system can be solubilized in surfactant micelles, dissolved in the surrounding solution, sorbed directly on the soil, or sorbed in association with sorbed surfactant. The presence of nonionic surfactant micelles in the bulk solution of the system results in the partitioning of the HOC between two bulk solution compartments, commonly referred to as pseudophases. The micellar pseudophase consists of the hydrophobic interiors of surfactant micelles, whereas the aqueous pseudophase consists mainly of dissolved surfactant monomers and water. Micelles form when the bulk solution concentration exceeds the surfactant CMC. 

In soil-aqueous systems, the hydrophobic interiors of nonionic surfactant micelles can compete strongly with soil organic matter as a compartment for the partitioning of HOCs. Surfactant micelles in such systems can markedly increase the bulk solution fraction of the total HOC mass, and micellar surfactant flushing has consequently been considered as a potential means for remediating soils contaminated with sorbed HOCs (4-6). Relatively little is known, however, about the physicochemical interactions of surfactants with HOCs and soil. 

Figure 1. Distribution of HOC and nonionic surfactant in soil-aqueous systems.

Figure 2. Schematic representation of physicochemical phenomena affecting microbial mineralization of nonionic-surfactant-solubilized HOC in soil-aqueous systems (not drawn to scale).

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. 

Figures 3 and 4 show good agreement between the experimental data and the solubilization values predicted by the model. Apparently the more important physical and chemical processes can be characterized with parameter values obtained from independent tests in aqueous and soil-aqueous systems. In addition, gross solubilization data alone can be used in an inverse procedure to calibrate the ratio between Kdcmc and (12).

Figure 3. Comparison of model prediction and experimental data for C PE solubilization of phenanthrene in the soil-aqueous system.

Figure 5. Microbial mineralization of phenanthrene in soil-aqueous system with...

Figure 6. Inhibition of phenanthrene mineralization in soil-aqueous systems receiving various doses of CI2E4 nonionic surfactant.

Figure 1. Surface-tension data indicate that micelle formation in the soil-aqueous system occurs at a surfactant dose of 0.09% (v/v) for the Cl2E4 nonionic...

Fig 3a A two-phase soil/aqueous system in the absence of surfactant. 

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