Photocatalytic Removal of Pesticides Present in Agro-industrial Water Effluents

Pesticide residues accumulated in agricultural wastewaters constitute a potential risk for the environment and the human health. Hence, focused actions for their elimination are of high priority for both the industry and national authorities. This work evaluates the effectiveness of the photocatalytic process to decompose four representative pesticides of different physicochemical properties; chlorpyrifos an organophosphate; thiamethoxam an neonicotinoid; flonicamid a pyridine and tebuconazole a triazole, frequently detected in the water effluents generated of the fruit-industry. Their photocatalytic degradation was examined using the commercial photocatalyst Evonik P25 TiO2 in a lab-scale batch reactor. The optimum conditions of the photocatalytic reactions were defined and the apparent reaction rate constants for the pesticide decomposition was determined. It was confirmed that the reaction rate depends on the pesticides concentrations (varying from 1 to 10 mg/L), the pH values of the solution (from strong acidic, to neutral and strong alkaline medium) and the presence of scavenger reagents (acting as reactive radicals quenchers). The photocatalytic efficiencies were evaluated taking into thorough consideration the compounds solubility and their adsorption onto the catalyst’s surface. Complete degradation of the selected pesticides was achieved after one hour illumination under UV-A light, without any formation of toxic by-products.