Efficient direct oxidation of medium/long chain petroleum hydrocarbons through migration of hydroxyl radicals by increasing soil polarity.

The application of Fenton technology in total petroleum hydrocarbon (TPH) contaminated soil has long been limited by the ineffective consumption of hydroxyl radicals (·OH) in water. The effect of polarity regulation on TPH oxidation was evaluated by adjusting the soil polarity (defined as η, which is the ratio of the integral area of hydrophilic functional groups -OH, -COOH and C-O-C to the proportion of humic acid), and by employing ·OH transfer ratio as an indirect indicator in this study. Results showed that when η increased from 149.38 to 227.47 (with ·OH transfer ratio of 64.38%), the oxidation amount of TPH increased from 4673 to 13,118 mg/kg (2.81 times); among which, the total oxidation amount of middle and long chain alkanes increased from 2816 to 9555 mg/kg (3.39 times); Fourier transform infrared spectroscopy (FTIR) analysis indicated that the total integral area of hydrophilic functional groups increased from 22.80 to 30.85. This suggests that the increase in soil hydrophilicity and polarity promoted the migration of ·OH from water to soil; the excitation-emission matrix spectroscopy (3DEEM) showed that the increase in the content of hydrophilic components in dissolved organic matter and the decrease in the relative proportion of humic acid led to an increase in the η. Therefore, the polarity regulation achieved an increase in the oxidation amount of middle and long chain alkanes by increasing the ·OH transfer ratio, and consequently resulted in an increase in the oxidation amount of TPH.