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In this work, the critical micellar concentration (CMC) for three anionic and nonionic surfactants was measured. The commercial products employed were Texapon 5 (sodium lauryl ether sulfate), Surfacpol 906 (ethoxylated nonylphenol), and Canarcel TW80 (ethoxylated sorbitan monooleate), and the CMC measured values were 0.941, 0.0934, and 0.05 mM, respectively. The diesel adsorption on sandy and clayey soils was characterized by means of the partition coefficients Kd, resulting in values of 0.5 and 1.4 mL/g for sandy and clayey soil, respectively. There are a few reports of Kd values for complex mixtures of organic compounds such as diesel. Retardation factors for every system were calculated, resulting in 2.6 and 2.9 for the sandy and the clayey soil, respectively. Interestingly, the retardation factors for both soils are quite similar, even when the diesel-soil partition coefficient for clayey soil is threefold the value for the sandy soil. Finally, diesel-removal efficiencies for the three surfactants from an aged contaminated sandy soil were evaluated at the sub-CMC and supra-CMC levels, at concentrations of 0.5, 5, 100 and 300 times the CMC for every surfactant. The results of the soil's washing as a removal percentage were 46.4–74.2, 41.9–83.3, and 52.5–88.2% for Texapon 5, Canarcel TW80, and Surfacpol 906, respectively. Experimental data were recalculated according to an equation where foc/Kd is a function of the total surfactant dose [D]. The experimental behavior for concentrations between 0.47 and 47 mM for Texapon, 0.025 and 2.5 mM for Canarcel, and 0.046 and 4.66 mM for Surfacpol was predicted by the mentioned equation. After these values, the foc/Kd values increased at a very accelerated rate, especially for the case of Surfacpol.
Luis G. Torres has experience in industrial wastewaters' biological treatment and characterization/remediation of metal and/or petroleum-contaminated soils. Currently, he has focused his interest on surfactant application to environmental problems. His main research lines are (a) surfactant-enhanced biodegradation of aged petroleum fractions in soils, (b) in-situ and ex-situ soil washing, and (c) preparation of petroleum fractions-surfactant-water emulsions as a first step for fuel's biotreatments (e.g., biodesulfuration).Jose L. Orantes has a bachelor's degree in mechanical engineering and a master's degree in environmental engineering, both by the Universidad Nacional Autónoma de México. He has experience on soil-washing aspects, particularly in the determination of critical micellar concentration values, adsorption-desorption isotherms, and surfactants' removal efficiencies measurements. Currently, he works in the dairy industry in Chiapas, Mexico.
Rosario Iturbe has a Ph.D. in hydraulic engineering by Universidad Nacional Autónoma de México. She has great experience on contaminants migration, ground-water contamination and remediation, and petroleum-contaminated soils characterization and treatment by means of physichochemical and biological processes (i.e., in-situ and ex-situ soil washing, biopiles, air soil vapor extraction, surfactant-enhanced biodegradation of aged petroleum fractions). Currently, she is a researcher and group leader at the Environmental Engineering Department of the Engineering Institute, Universidad Nacional Autónoma de México.