Imidacloprid removal by fluidized-bed Fenton process

Imidacloprid (IMD) is a new type of the insecticides widely used in agriculture and wastewater containing IMD can harm human and aquatic lives. This study used the fluidized-bed Fenton process to remove IMD because of its low capital cost, easy operation, and non-toxic byproducts after treatment. Degradation of IMD was investigated in a bench-scale reactor with synthetic wastewater. Studied conditions included pH 2-5, 1.0-10.0 mM of Fe²⁺, 1.0-15.0 mM of H₂O₂, 1.0 mM of IMD, 1-5 times of bed expansion, and 100 g of SiO₂. It was found that the Fe²⁺:H₂O₂ molar ratio was a significant operating factor on IMD degradation and the optimum ratio was 3:5. Increasing H₂O₂ concentration could improve IMD degradation; however, excessive H₂O₂ caused OH^• scavenging effects and decreased IMD degradation as a consequence. When the initial Fe²⁺ concentration increased, the IMD degradation and H₂O₂ decomposition efficiencies also increased rapidly. Scavenging of OH^• by Fe²⁺ was not observed in all the Fe²⁺ dosages used in this study. Under the appropriate conditions, the degradation efficiencies in term of IMD, COD, and TOC of 97.07%, 41.38%, and 12.04%, respectively, could be obtained within 45 minutes of the reaction period at pH 3.0. Total iron was removed up to 40% via heterogeneous nucleation onto SiO₂ surface. Increasing bed expansion slightly deteriorated total iron removal performance due to scouring effect.