Treatment of Soil-Washing Effluents Polluted with Herbicide Oxyfluorfen by Combined Biosorption-Electrolysis

Abstract

The treatment of soil-washing effluents polluted with herbicide oxyfluorfen is studied using a combined process consisting of biosorption and electrolysis. Results show that oxyfluorfen is very efficiently removed from synthetic soil by soil washing with sodium dodecyl sulfate (SDS). The effluent can be treated by biosorption with fresh activated sludge coming from a municipal wastewater treatment plant, and the maximum adsorption capacity of this activated sludge was found to be 18 mg of oxyfluorfen per gram of biomass. Biosorption fits well to a type I adsorption isotherm. Effluents of the biosorption process underwent anodic oxidation, photoelectrolysis, and sonoelectrolysis at high and low frequency. The four technologies were able to mineralize completely the effluent, although important differences arose during the treatment which depended significantly on the application of ultrasound or ultraviolet irradiation and on the release of sulfate from the oxidation of SDS: intermediates were removed faster because of the activation of sulfate radicals. Oxyfluorfen and its oxidation intermediates are removed faster than SDS, and when they are fully depleted there are still large concentrations of SDS in the treated solution. This opens the possibility of reusing the soil washing fluid.