Abstract
In this work, it is studied the treatment of soil polluted with oxyfluorfen by Surfactant-Aided Soil-Washing (SASW) and after that, photo-electrolysis was used for the treatment of the soil-washing fluid produced. This liquid waste is characterized by the high concentration of micelles of pesticide and surfactant (sodium dodecyl sulfate, SDS), whose initial size depends on the ratio soil-surfactant used in the soil washing treatment. The waste treatment is studied in terms of the decrease in size of the particles and the depletion of the pollutants. Results clearly demonstrate that photo-electrolysis with diamond electrodes is a very effective treatment technology with results that overcome those obtained by single photolysis and/or single electrolysis with diamond electrodes. The greater improvements attained by combining UV irradiation to the electrolysis were observed in the removal of the pesticide while the removal of the surfactant was little affected. Electrolysis does not only deplete the complete concentration of pesticide but it also shows to be very efficient in the depletion of the surfactant, preventing its potential recycle. The significant concentration of sulfate released during the attack to the surfactant and the effect of the peroxosulfate anions that are formed from the anodic oxidation of that anion, explain the improved performance of the technology in the treatment of washing fluids with higher concentrations of SDS.
Highlights
Over the last years, the search for novel sources of water has become a topic of the major interest, in particular in countries with serious problems of permanent or stationary lack of water
88% and 96% of total organic carbon (TOC) by using BDD and DSA-Cl2 anodes, showing clearly a synergistic combination. Taking into account this background, the objective of this study is to investigate the remediation of soils polluted with oxyfluorfen (Figure 1) by a combined treatment consisting of the surfactant-aided soil washing (SASW) with a sodium dodecyl sulfate (SDS) solution followed by the photolysis and/or photo-electrolysis with conductive-diamond anodes of the soil-washing fluid
The soil-washing process by using surfactant is an ex situ process that improves the removal of contaminants sorbed to soil [32], enhancing the contact between extracting agents and soil pollutants, thereby allowing better transference of the pesticide from the soil matrix into a simpler and easier liquid phase to be treated
Summary
The search for novel sources of water has become a topic of the major interest, in particular in countries with serious problems of permanent or stationary lack of water. We are far away from the development of an efficient treatment technology, robust enough to transform wastewater into high quality water and this fact explains the huge interest paid by the scientific community to Advanced Oxidation Processes in the recent years [1,2,3] Among those technologies, electrolysis with diamond anodes has received considerable interest for the removal of very different types of pollutants in the recent years [4,5,6,7,8,9] because of its outstanding efficiency, explained in terms of the combination of direct (by electron transfer) and mediated (through the formation of oxidizing/reducing agents at the electrode) oxidation approaches [8, 10]. Three important aspects should be taken into account: (i) the dosage of the precursor for the production of oxidants (i.e., Cl-, SO42-, CO32- etc,), but preferentially it should be contained in wastewater to avoid the undesired salinization of the waste, (ii) the oxidant produced on the electrodes should be efficient for the oxidation of pollutant contained in wastewater, (iii) sometimes, the oxidant produced is not active for the oxidation of the pollutant but it could be activated
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