Impact of ultrasonic power density on hot water elution of severely biodegraded heavy oil from weathered soils.

An ultrasound-enhanced elution system using water at a temperature of 70 degrees C was employed to remove severely biodegraded heavy oil (SBHO) from weathered soil. The effect of varying the ultrasonic power density from 0 to 100 W L(-1) on the elution of SBHO and three characteristic biomarkers (C(26-34) 17alpha 25-norhopanes, C(26-28) triaromatic steroids (TAS), and C(27-29) methyl triaromatic steroids (MTAS) was analyzed using GC/MS, scanning electron microscopy (SEM), and X-ray diffraction (XRD). The amount of SBHO and biomarkers present in the treated soils and eluent had significant negative correlation with increasing ultrasonic power density. Elution of the three biomarkers was closely related to the number of C atoms in the marker: C(26-34) 17alpha 25-norhopanes with more carbon numbers and MTAS homologs with less carbon numbers were more readily eluted at higher power densities. The smaller TAS species were more readily eluted at a power density of less than 60 W L(-1), while larger TAS species displayed improved elution at power densities greater than 60 W L(-1). SEM images of samples treated at higher power densities revealed a more compact SBHO accumulation layer at the water-soil interface. The results of XRD and energy spectroscopy experiments indicated that ultrasound at a power density of 20 W L(-1) was helpful for the formation and sedimentation of calcite, although this effect disappeared at higher power of greater than 60 W L(-1).