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Study on the cotransport of the polymer chitosan in the presence of the insecticide λ-cyhalothrin in porous media under static and dynamic conditions

Xenou Evangelia-Apostolia

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Summary

Potable water is one of the vital needs for the survival of organisms and its demand is growing rapidly. In recent decades, surface and groundwater have been heavily polluted by industrial, urban wastewater and agricultural runoff. Most of the currently available technologies are inadequate to remove pesticides and their pigments from cropland and then avoid their transport to the subsoil. To alleviate the environmental pressure from the overuse of conventional pesticides, the study of a new environmentally friendly and multi-functional formulation is urgent. The interest in polymers such as Chitosan, as well as its application methods in various fields of science, is growing steadily. Due to its unique physicochemical, biological, ecological properties such as biocompatibility, biodegradability, non-toxicity, affordability, and high absorption properties, justify its widespread use in various industrial processes. λ-Cyhalothrin is a hydrophobic insecticide belonging to the pyrethroid class and is very often found in agriculture because of its high yields. However, its dispersion in the subsoil and thus in the aquifer may result in toxic environmental impact and other ecological nuisances. The search for knowledge of the fundamental forces and mechanisms responsible for uptake in different soil and pesticide systems continues, and the need to consider the consequences for the behavior of pesticides in soil and water systems has increased rapidly in recent years. Adsorption has been identified as a potential technology for the removal of pesticides, dyes and other contaminants from wastewater. Compared to other physical, chemical and biological methods available for wastewater treatment, adsorption is the most preferred technique due to its simple and flexible design and smooth operation. The adsorption process can produce little or no toxic pollutants and involves low initial capital and subsequent operating costs.In this study, the absorptivity of Chitosan to l-Cyhalothrin through porous media is investigated as it could be an innovative alternative for environmental remediation and to understand the contribution of the contaminant to the subsurface. Three series of experiments were carried out to extract data. Firstly, Batch experiments were carried out under static and dynamic conditions to study the interaction of Chitosan and l-Cyhalothrin. Then, the same experimental setup was studied with the difference of adding quartz sand, a material that simulates a large part of the soil layer. Various parameters were chosen to conduct the intermittent work experiments to cover a wide range of combinations found in nature. More specifically, different concentrations of l-Cyhalothrin (25mg/L, 50mg/L, 100mg/L) were prepared, while the concentration of Chitosan was constant in all experiments (100mg/L). Then the pH variable was varied (5, 6.5, 8) and finally solutions with different ionic strengths (1mM, 50mM, 100mM) were prepared, where the temperature was kept constant throughout at 25 °C. In all the above experiments, values for the size and zeta potential of the aggregates were obtained to implement further comparison of the parameters. Finally, Packed Column Experiments under saturation conditions were carried out to study the effect of quartz sand and pore water velocity on Chitosan and l-Cyhalothrin transport. In order to form a comprehensive view on the subject, apart from conducting experiments with a combination of the two materials, separate experiments were carried out to study the transport characteristics. Indeed, the solution composed of both materials had the optimal result, which validates that the Chitosan polymer plays an important role in the adsorption of the insecticide l-Cyhalothrin in the subsoil. The ColloidFit software was used to process the experimental data, where the data were simulated very closely according to the pseudo-second order adsorption kinetic model. It is therefore suggested that the predominant phenomenon in all series of experiments was that of chemical adsorption.

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