- Copyright ©2008. The American Association of Petroleum Geologists/Division of Environmental Geosciences. All rights reserved.
A soil contaminated with petroleum hydrocarbons, arising from an old Mexican refinery, was previously characterized in terms of total petroleum hydrocarbons (TPHs), diesel and gasoline fractions, benzene-toluene-ethylbenzene-xylene (BTEX), polycyclic aromatic hydrocarbons (PAHs), and some metals. A health risk analysis determined that some PAHs should be reduced, and the Mexican standard indicates that high TPHs concentrations must be reduced to 2000 mg kg−1. This soil was submitted to a surfactant-enhanced washing using sodium dodecyl sulfate (SDS) with and without NaCl, polyethoxylated sorbitan monoleate (TW80), and polyethoxylated nonylphenol (E600) (an anionic and two nonionic surfactants) at different concentrations. Based on these experiments, it was decided to wash soils with given doses of each surfactant in a continuous system, where 9 kg of soil was washed alternatively with surfactant solutions and plain water during 42 days. After this process, soils were drained, dried, and milled. Parameters, such as microbial count, total N, organic carbon and organic matter, available P, pH, dry and bulk densities, electrical conductivity (as a measure of salts content), Na, K, Ca, and Mg, were measured before and after the washing process. In general, all parameters were affected by the soil washing, but the most interesting changes were the increases in organic matter, electrical conductivity (for the experiments in which SDS was used), phosphorus, and total nitrogen (except for the experiment with TW80). Log total heterotrophs count was reduced to one half in most experiments, and Na and Mg were, in general, diminished, whereas K and Ca were augmented because of the surfactant soil washing. However, statistical analysis (analysis of variance [ANOVA]) indicated that only electrical conductivity and phosphorus were significantly affected (p < 0.05). Changes are discussed and compared with changes occurring in soils caused by different nonanthropogenic events such as acid rain, organic fertilization, reseeding with native species, amending of soils with manure, etc.
Rosario Iturbe received her Ph.D. on hydraulic engineering from UNAM. She has great experience on contaminants migration; groundwaters contamination; and remediation, 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, and surfactant-enhanced biodegradation of aged petroleum fractions). Currently, she is a researcher and group leader of the Soil and Aquifers Remediation group at the Environmental Engineering Department of the Engineering Institute, UNAM.
Jessica Lopez studied environmental engineering at UPIBI-IPN, Mexico. Afterward, she received her M.S. degree in environmental engineering from UNAM, Mexico. Today, she works in the Environmental Engineering Department of the Engineering Institute as a specialized technician in the Soil and Aquifers Remediation group. This work is part of her M.S. degree experimental work.
Luis G. Torres has experience in industrial wastewaters' biological treatment and characterization and remediation of metal and/or petroleum-contaminated soils. Currently, his interest is on the surfactant's application to environmental problems. His main research lines are surfactant-enhanced biodegradation of aged petroleum fractions in soils, in-situ and ex-situ soil washing, preparation of petroleum fractions-surfactant-water emulsions as a first step for biotreatments of fuels (e.g. biodesulfuration), and rheology and mixing of sludges and suspensions applied to environmental problem solutions.