Assessing the application of a biochar-supported iron oxide catalyst to the treatment of imidacloprid by photo-Fenton technologies

Abstract

Emerging contaminants entail a great challenge to conventional treatment systems because they are not able to remove most of these bio-recalcitrant compounds. In particular, the presence of pesticides, such as imidacloprid, in the environment is a great hazard to soil microbiota, pollinating insects, and the aquatic environment. This research aims to enhance the treatment efficiency of advanced oxidation processes applied to the removal of bio-recalcitrant pollutants that are present in stormwater by assessing the application of a newly designed, economical, and efficient treatment alternative. Specifically, solar and LED (365 and 420 nm) heterogeneous photo-Fenton processes were carried out to remove a concentration of 5 mg·L−1 of imidacloprid, which was selected as the model pollutant that has been identified present in stormwater, using a magnetic iron oxides catalyst supported on pinewood waste biochar. The removal kinetics and mineralization of this contaminant were determined under the effect of the natural pH value of the solution and under a circumneutral pH environment, and heterogeneous and homogeneous catalytic contributions to the process were assessed. All these treatments achieved the successful efficient removal of the contaminant whether applying LED (UVA or visible blue) or solar radiation. The heterogeneous photo-Fenton treatment using a magnetic iron oxide catalyst supported on pinewood waste biochar totally removed imidacloprid after 10 minutes of oxidation at the initial natural pH value of the solution using 365 nm UVA LED radiation. Moreover, a 70% TOC removal was addressed after 60 minutes of treatment. The solar version of this heterogeneous photo-Fenton process removed the contaminant after 60 minutes of reaction, together to a TOC removal of the 60–65% after 120 minutes of treatment, including certain photolytic contribution; as well as it showed very efficient results under the effect of a circumneutral pH value. The assessed biochar-supported iron oxide catalyst was displayed as very stable under all the tested reaction conditions and its heterogeneous contribution to the process was confirmed superior to an exclusive homogeneous process.