The use of a combined process of surfactant-aided soil washing and coagulation for PAH-contaminated soils treatment

Abstract

Polycyclic aromatic hydrocarbons (PAHs) persist in soils due to their low volatility, low water solubility and low biodegradability, all of which make it difficult to remove this type of compound from soils. The work described here involved the study of a combined surfactant-aided soil washing (SASW) process and coagulation treatment, using iron and aluminium salts, to remediate a low-permeability PAH-polluted soil. Phenanthrene was selected as the model PAH and three different types of surfactants (anionic, cationic, and non-ionic) were used as washing agents. The results show that the anionic surfactant is the most effective washing fluid because efficiencies higher than 90% can be achieved. Non-ionic and cationic surfactant efficiencies were 70% and 30%, respectively. In addition, only the anionic wastewater can be satisfactorily treated with this technology, with COD removals greater than 90% achieved. Variation of pH, zeta-potential and the dose of aluminium required seem to indicate that a charge-neutralization mechanism is the main process involved in the emulsion break-up obtained in the treatment of aqueous surfactant wastes. In addition, the effects of surfactant concentration and that of the pH of the soil-washing wastewater seem to have a greater influence on the performance of the coagulation process.