Soil Washing for Reduction of Aromatic and Aliphatic Contaminants in Soil

The extraction of crude oil worldwide is estimated to be about 4 billion tons annually, 10% of which leaks into the environment. Iran is in great risk of pollution because of the extensive natural oil reservoirs and the spread of the oil industry. During the past 10–15 years soil washing methods have gathered much attention due to their rapid and easy implementation and high clean up efficiencies in removing organic contaminants from polluted soils. This paper investigates the effects of soil washing at various temperatures and pH levels of the washing solutions on the removal of gasoline constituents from contaminated soils. Aliphatic and aromatic fractions of gasoline were studied for this purpose. Raw soil samples were spiked with gasoline for soil washing tests. Sodium dodecyl sulfate surfactant (with concentration of 1 g/L) was used as the washing solution for the samples. The results of this study indicate that an increase in both pH and temperature of the solution enhances the removal efficiencies of aliphatic and aromatic contaminants from soil samples. The removal efficiencies of aliphatic contaminants from coarse and fine fractions of the samples increased from 81.12 to 92.34% and 62.41 to 76.47%, as the temperature rose from 20 to 40°C, respectively. A nearly similar trend of increase was noted for the aromatic compounds. With regard to pH of the washing solutions, the removal efficiencies of the contaminants increased as the pH changed from 5.76 to 8.14. Thus, concluding that the implementation of soil washing is more efficient when the soil has naturally high pH values. The results of the study indicate that sand and gravel presented the highest removal efficiencies (92.34 and 92.39%) for both aliphatic and aromatic contaminants at 40°C. These values were almost 11% higher than the samples tested at room temperature. It could be concluded that an increase in temperature could enhance the movement of the reagent molecules.