Magnetic biochar pyrolyzed from municipal sludge for Fenton-like degradation of thiamethoxam: Characteristics and mechanism

Abstract

Pesticide pollution is an arduous challenge encountered in the field of industrial wastewater treatment. As a Fenton-like metal catalyst, multifunctional biochar has attracted more and more attention in the dissolution of insoluble organic chemical pollutants. In this study, the magnetic municipal sludge biochars(MSDBC)were synthesized by one-step pyrolysis of sludge from sewage treatment plant. The biochars prepared at different temperatures have great differences in surface functional groups and composition of iron phase. MSDBC prepared at 400 °C has a better catalytic oxidation capacity, while MSDBC prepared at 800 °C has a stronger adsorption capacity. The reason is that the morphology and iron phase composition distribution of biochar are different. More pore structures were formed on the surface of biochar prepared at 800 °C, which not only has better adsorption performance, but also makes the impregnated Fe3+ enter the interior of biochar and transform during pyrolysis. However, the iron phase of MSDBC prepared at 400 °C is mostly located on the surface and the content of Fe2+ is higher. Notably, iron compounds embedded in the magnetic biochar have been proved to be the main catalysts for activating hydrogen peroxide (H2O2) to produce hydroxyl radicals (·OH). Radical quenching experiment and electron paramagnetic resonance (EPR) detection confirmed the production of ·OH and its important role in the oxidative degradation of thiamethoxam (THX). In the THX degradation, MSDBC/H2O2 Fenton-like system showed excellent effect at neutral pH environment. Finally, the innovative use of MSDBC/H2O2 Fenton-like technology in the degradation of complex actual wastewater showed good practicability and stability. This research provides a new idea for the treatment of pesticide wastewater.