Sorption characteristics of a nonionic surfactant during remediation of contaminated soil with different organic content

Surfactant enhanced subsurface remediation has gained importance in soil remediation. Since surfactants can be sorbed on soils, the concentration of free surfactant could drop below the critical micelle concentration, CMC, which may reduce the ability of the surfactant to solubilize the contaminants in soils. ^ The main goal of this research was to study the factors affecting the surfactant sorption on soil such as surfactant concentration, soil organic content, and organic contaminants in soil and to determine the organic contaminants removed from soils by surfactant. The results would be served as the basis for the implementation of a future study in the pilot scale and field scale for surfactant enhanced subsurface remediation. ^ This research study investigated the relationship between the organic content of soils and the sorption characteristics of a nonionic surfactant, Triton X-100. The experiments were performed using uncontaminated soils and soil contaminated with naphthalene and decane. The first part of the experiments were conducted in batch mode utilizing surface tension technique to determine the CMC of surfactant Triton X-100 and the effective CMC in the soil/aqueous system. The sorption of Triton X-100 was calculated from the surface tension measurements. The second part of the experiments utilized the SPME/GC/FID technique to determine the concentration of the contaminants solubilized from the soils by the surfactant Triton X-100 at different concentrations. ^ The results indicated that when the concentration of surfactant was lower than the CMC, the amount of surfactant sorbed on soil increased with the increasing surfactant concentration and the surfactant sorption characteristics of the uncontaminated soils could be modeled by the Freundlich isotherm. For the contaminated soils, the amount of surfactant sorbed was higher than those for the uncontaminated soils. The amount of surfactant sorbed on soils also depends on the organic content in the soils. The higher the organic content in the soil, higher is the amount of surfactant sorbed onto the soil. When the concentration of surfactant was higher than the CMC, the amount of surfactant added into the soil/aqueous system will increase the number of micelle and it increase the solubilization of organic contaminant from the soils. The ratio of the moles of organic contaminant solubilized to the moles of surfactant present as micelles is called the molar solubilization ratio (MSR). MSR value for naphthalene was about 0.16 for the soil-water systems. The organic content of soil did not appear to affect MSR for naphthalene. On the other hand, the MSR values for decane were 0.52, 0.39 and 0.38 for soils with 25%, 50% and 75% organic content, respectively. ^

Formation of Polycyclic Aromatic Hydrocarbons and Nitrogen Containing Polycyclic Aromatic Compounds in Titan's Atmosphere, the Interstellar Medium and Combustion

Several different mechanisms leading to the formation of (substituted) naphthalene and azanaphthalenes were examined using theoretical quantum chemical calculations. As a result, a series of novel synthetic routes to Polycyclic Aromatic Hydrocarbons (PAHs) and Nitrogen Containing Polycyclic Aromatic Compounds (N-PACs) have been proposed. On Earth, these aromatic compounds originate from incomplete combustion and are released into our environment, where they are known to be major pollutants, often with carcinogenic properties. In the atmosphere of a Saturn's moon Titan, these PAH and N-PACs are believed to play a critical role in organic haze formation, as well as acting as chemical precursors to biologically relevant molecules. The theoretical calculations were performed by employing the ab initio G3(MP2,CC)/B3LYP/6-311G** method to effectively probe the Potential Energy Surfaces (PES) relevant to the PAH and N-PAC formation. Following the construction of the PES, Rice-Ramsperger-Kassel-Markus (RRKM) theory was used to evaluate all unimolecular rate constants as a function of collision energy under single-collision conditions. Branching ratios were then evaluated by solving phenomenological rate expressions for the various product concentrations. The most viable pathways to PAH and N-PAC formation were found to be those where the initial attack by the ethynyl (C2H) or cyano (CN) radical toward a unsaturated hydrocarbon molecule led to the formation of an intermediate which could not effectively lose a hydrogen atom. It is not until ring cyclization has occurred, that hydrogen elimination leads to a closed shell product. By quenching the possibility of the initial hydrogen atom elimination, one of the most competitive processes preventing the PAH or N-PAC formation was avoided, and the PAH or N-PAC formation was allowed to proceed. It is concluded that these considerations should be taken into account when attempting to explore any other potential routes towards aromatic compounds in cold environments, such as on Titan or in the interstellar medium.