Soil remediation using soil washing followed by Fenton oxidation

Soil washing was applied to a contaminated soil with p-Cresol by using a nonionic surfactant (Tween 80). A mathematical model has also been proposed to describe both the pollutant desorption and the surfactant adsorption, taking place simultaneously. The effect of temperature (20–40 °C) and surfactant concentration (0.1–10 g L−1) have been analyzed on both kinetic rates. The kinetic desorption rate of p-Cresol increases as the initial solubilizer concentration. Desorption of p-Cresol was slightly greater with increasing temperature. The obtained kinetic model represents quite well the experimental results.Soil washing wastewater (20 mg L−1 of p-Cresol and 0.86 g L−1 of Tween 80) has been treated with Fenton Reagent to remove the pollutant extracted (p-Cresol) and to recover the surfactant solution. The pH of the soil washing wastewater was about 6.5 and did not change significantly during the Fenton Reagent treatment. Total conversions of p-Cresol were observed, at very short times, at the conditions tested for the Fenton reaction (100 mg L−1 of H2O2 and 10 mg L−1 of Fe2+). The hydrogen peroxide was not totally exhausted, showing conversions near 60% at 120 min. Besides, the removal of Tween 80 during the Fenton’s reaction was lower than 10%, which suggests that the reaction is mainly selective to p-Cresol degradation. The toxicity of the liquids, measured by Microtox bioassay, was significantly reduced after the oxidation reaction, suggesting the negligible formation of degradation intermediates with higher toxicity than p-Cresol.

► Soil washing with a nonionic surfactant Tween 80 was analyzed.
► A model considering surfactant adsorption and p-Cresol extraction was proposed.
► Soil washing was used in combination with Fenton oxidation.
► Reaction is selective to the contaminant degradation.
► Reaction allows the recovery and reuse of the surfactant.