ULTRASOUND-ASSISTED EXTRACTION OF PAH-CONTAMINATED CLAY SOIL IN THE MIDDLE YANGTZE RIVER BASIN, CHINA: OPTIMISATION WITH RESPONSE SURFACE METHODOLOGY

The continuous increase in oil production has led to the contamination of soil and water ecosystems. Contamination results in negative effects. Polycyclic aromatic hydrocarbons (PAHs) persist in soil because of their low volatility, low solubility and low bioavailability. Thus, PAH removal using conventional surfactant washing is difficult. Laboratory experiments were conducted using anionic washing agent sodium dodecyl sulphate (SDS) combined with ultrasound to optimise phenanthrene recovery efficiency from contaminated clay soil. We investigated the following process parameters that affect the efficiency of the recovery process: temperature (30 degrees C to 60 degrees C), SDS concentration (242 mg/L to 726 mg/L) and ultrasonic time (10 min to 20 min). A response surface methodology based on Box Behnken statistical experiment design was applied to analyse the experimental variables. All variables showed a positive effect on phenanthrene recovery efficiency. Interactions between temperature and SDS concentration and between temperature and ultrasonic time were significant, whereas the interaction between SDS concentration and ultrasonic time was insignificant. Under optimal conditions, the predicted and observed recovery efficiencies were 73.67% and 74.32%, respectively. Results confirmed that the model was accurate and reliable for analysing the variables of ultrasound-assisted surfactant extraction treatment.