Treatment of soil contaminated with petroleum hydrocarbons using activated persulfate oxidation, ultrasound, and heat: A kinetic and thermodynamic study

This study focuses on the remediation of petroleum hydrocarbons in the soil matrix. Factors such as the per sulfate dosage, initial pH, temperature, ultrasonic power, and soil water ratio were investigated by using ultrasonic and thermal energy to activate persulfate. The results showed that the degradation efficiency of the total petroleum hydrocarbon (TPH) content was 78.2% and 72.64% within 72 h for the ultrasonically/thermallyactivated persulfate ("US/Heat/PS") and thermally-activated persulfate ("Heat/PS") systems, respectively, whereas it was 56.41% for the ultrasonically-activated persulfate system. The results of the kinetics analysis suggested that the degradation of petroleum hydrocarbons well-fitted the pseudo-second-order reaction, and that the rate constants increased with increasing temperature and initial persulfate dosage but with decreasing pH over a certain range. Moreover, three reaction phases comprising two rapid phases and an intermediate phase were observed for the TPH degradation. The measured thermodynamic parameters justified the spontaneity of the degradation process. Furthermore, a possible mechanism of petroleum hydrocarbon degradation in the US/Heat/PS system was determined through gas chromatography-mass spectrometry analysis, and the degradation priority of different components was ranked as: alkenes > alcohols > esters > alkanes > aromatics.