Removal of pendimethalin from soil washing effluents using electrolytic and electro-irradiated technologies based on diamond anodes

doi:10.1016/j.apcatb.2017.05.008

Applied Catalysis B: Environmental

Volume 213, 15 September 2017, Pages 190-197

https://doi.org/10.1016/j.apcatb.2017.05.008 Get rights and content

Highlights

•
Pendimethalin can be extracted from soils using surfactant-added soil-washing.
•
Electrolysis decreases simultaneously the herbicide and surfactant concentrations.
•
Sulfate ions are released from the electrochemical oxidation of surfactant.
•
Electro-irradiated technologies improve slightly the electrolysis of SWF.
•
Photoelectrolysis is the best technology for the treatment of SWF.

Abstract

This work describes the treatment of soil polluted with the herbicide pendimethalin by the combination of surfactant-aided soil-washing (SASW) and electrochemical advanced oxidation processes. Results show that it is possible to completely extract the herbicide from soil using SDS (sodium dodecyl sulfate) solutions as soil washing fluid (SWF) and ratios SWF/soil higher than 10 dm³ kg⁻¹. Soil washing effluents obtained after the application of the SASW consisted of a mixture of surfactant (high concentration) and pesticide (low concentration) and their degradation by electrolysis, photo-assisted electrolysis (photoelectrolysis) and sonoelectrolysis with diamond anodes has been compared with that obtained by the application of single photolysis and sonolysis. Opposite to photolysis and sonolysis, the different electrolytic techniques allow decreasing the concentration of herbicide and surfactant in the effluents. Competition between the surfactant and the herbicide oxidation is important and irradiation of high-frequency ultrasound or UV light do not seem to outperform very importantly the results obtained by single electrolysis in the effluents of the SASW obtained with low SDS/soil ratios. Opposite, photoelectrolysis becomes the most efficient technology for the treatment of SWF obtained at high SDS/soil ratios (those required for an efficient SASW). Catalytic effect of the sulfate released during the degradation of SDS (in particular the formation of sulfate radicals) can help to explain the differences observed. The removal efficiency is higher during sonoelectrolysis, reaching a final removal of the pesticide after 8 h of treatment of 86.22%. Photoelectrolysis (57.59%) shows higher efficiencies for the removal of SDS followed by sonoelectrolysis (52.64%) and, finally, electrolysis (48.29%), after 8 h of treatment.

Graphical abstract

Introduction

Over the last seventy years, the increasing use and the hazardousness of organic pesticides has alarmed to environmental authorities which, in turn, have favor the application of a stricter regulation about the manufacturing and application of these agrochemicals. Nowadays, many products, which have been widely applied for decades, are banned in many countries and there is an important search of technologies capable to minimize the impact of the pesticides which are still in use, in order to control their diffusion and to minimize their negative impacts on human health and environment.

Among pesticides, herbicides are able to rapidly remove the weed of crops. They have to be applied in large concentrations and the interaction with the soil matrix may be important. For this reason, their presence is not only limited to soils but they can also be present in groundwater in significant concentrations. Furthermore, these compounds can be found in soils because of accidental discharges and, in this case, the concentration of herbicides can be much higher than that found from agricultural activities. Hence, it is necessary to develop clean and efficient technologies that allow an efficient removal of these compounds from both, soil and water.

One of the most applied technologies for the treatment of different pollutants from soils is soil washing, which is considered as an excellent technique due to its simplicity and high efficiencies reached in the removal of various types of pollutants [1], [2], [3]. This process consists of a physical treatment, where the pollutant is transported from soil to a liquid stream, commonly called Soil Washing Fluid (SWF). To obtain high efficiencies with this technology, it is essential to attain an efficient mass transfer of the pesticide from soil to the liquid stream and, in the case of pollutants with low solubility in water, it can be needed the use of surfactants during the treatment and this process is known as SASW, Surfactant-Aided Soil-Washing [4], [5]. Anyhow, the outcome of soil washing technology is a treated soil and a highly-polluted soil washing fluid, which needs for additional treatment.

Electrochemical processes are among the most promising technologies for the treatment of soil washing effluents polluted with organics [6], [7], [8], [9], [10]. Specifically, electrolyses with diamond electrodes have been proven efficient in the removal of different types of pollutants from wastewater, reaching a total mineralization of the organic matter [11], [12], [13], [14], [15], [16]. This technology is based on the generation of powerful oxidants from the oxidation of the ions naturally contained in wastewater [17]. Likewise, diamond anodes favor the generation of large amounts of hydroxyl radicals during wastewater treatment which, in turn contribute to the mineralization of the organic matter [18]. Nonetheless, the main drawback of the electrolytic technology is the mass transfer limitations associated to the transport of the pollutant to the anode surface. For this reason, to overcome this limitation, the electrochemical oxidation can be coupled with other processes such as US (sonoelectrolysis) and UV light irradiation (photoelectrolysis) [19], [20]. In this context, the use of ultrasound waves or UV light may promote the activation of the oxidants electrogenerated, favoring the formation of free radicals. These species significantly contribute to the mineralization of the organic matter [21], [22], [23].

One of the most commonly-used herbicides is pendimethalin (C₁₃H₁₉N₃O₄). This is a nitro-organic compound that allows preventing the growth of weeds in different crops such as garlic, artichoke, cotton, barley and onion. However, this compound can promote different types of cancer in humans and, therefore, should be removed from water [24]. Despite its extended application, there are few works in literature related to its degradation. Thus, Pinto et al. [25] studied the removal of pendimethalin by fungi cultures. They described the application of different fungi for the biodegradation of pendimethalin showing that Lecanicillium saksenae (L. saksenae) could remove 99.5% of the chemical in batch liquid cultures. Another study was carried out by Fenoll et al. [26], who described the photodegradation of pendimethalin in drinking water at pilot plant scale. They proposed the use of the ZnO catalyst for the removal of the pesticide, reaching a final concentration lower than 0.8 μg dm⁻³. More recently, Ahammed Shabeer et al. [27] carried out the removal of pendimethalin by a combined adsorption-coagulation-flocculation using aluminum and polyaluminum chloride as coagulants and modified montmorillonites and bentonite as adsorbents. They demonstrated that the combined treatment was much more efficient than single processes. Thus, this combined technology allowed removing higher than 90% of the herbicide.

Nevertheless, its treatment by electrochemical technology has not been reported and, in addition, the literature only includes the degradation of the herbicide in water but not in soils, where the impact can even be higher. Taking into account this background, the main aim of the present work is to evaluate the application of a combined soil washing-electrolysis treatment for the removal of pendimethalin from spiked soil. The influence of the ratio surfactant/soil has been studied during soil washing and electrolysis because it seems to have a clear influence in the kinetics and the removal efficiency. Furthermore, in order to try to improve the process performance, the coupling of US and UV light irradiation to the electrochemical process (sonoelectrolysis and photoelectrolysis, respectively) was evaluated during the electrochemical treatment.

Section snippets

Chemicals

Pendimethalin (3,4-dimethyl-2,6-dinitro-N-pentan-3-ylaniline) and sodium dodecyl sulfate (SDS) (Sigma-Aldrich, Spain) were analytical grade and used as received. Acetonitrile HPLC grade (Sigma-Aldrich, Spain) was used for the mobile phase. Sodium tetraborate decahydrate, sodium hydroxide, phenolphthalein, methylene blue and chloroform (Sigma-Aldrich, Spain) were used for the determination of surfactant. Sodium carbonate and acetone (Sigma-Aldrich, Spain) were used as mobile phase for the

Treatment of soil by SASW

In order to evaluate the efficiency of the soil washing in the removal of pendimethalin, several SASW tests were carried out to treat spiked soils with 100 mg kg⁻¹ of herbicide, using different surfactant/soil ratios. Fig. 1 shows the concentration of pendimethalin and SDS that remains in the soil after the application of the SASW process and Fig. 2 informs about the quality of the soil washing effluent produced in each of these tests.

From Fig. 1, it can be stated that the herbicide is completely

Conclusions

From this work the following conclusions can be drawn:

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Pendimethalin can be extracted from soils by SASW using SDS as surfactant. Ratios SDS/soil higher than 200 g kg⁻¹ ensure a complete extraction of the herbicide.
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Electrolysis with diamond anodes of soil washing effluents polluted with pendimethalin allows decreasing the pesticide concentration in the effluent. However, the removal efficiency in the removal of pendimethalin is limited by the competitive oxidation between the herbicide and the

Acknowledgements

Financial support from the Spanish Ministry of Economy, Industry and Competitiveness and European Union through project CTM2016-76197-R (AEI/FEDER, UE) is gratefully acknowledged. Universidad Autónoma del Estado de México, CONACYT and CYTEMA E2TP program of University of Castilla-La Mancha are also acknowledged for the grants to Perla T. Almazán-Sánchez and to Dr. Salvador Cotillas.

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Removal of pendimethalin from soil washing effluents using electrolytic and electro-irradiated technologies based on diamond anodes

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Chemicals

Treatment of soil by SASW

Conclusions

Acknowledgements

Chem. Eng. J.

Chemosphere

J. Hazard. Mater.

Eng. Geol.

Appl. Catal. B: Environ.

Ultrason. Sonochem.

Water Res.

J. Hazard. Mater.

Chem. Eng. J.

J. Environ. Manage.

Appl. Catal. B: Environ.

Chem. Eng. J.

Water Res.

Appl. Catal. B: Environ.

J. Hazard. Mater.

Electrochim. Acta

J. Hazard. Mater.

J. Electroanal. Chem.

Sci. Total Environ.