High Fe utilization efficiency and low toxicity of Fe3C@Fe0 loaded biochar for removing of tetracycline hydrochloride in wastewater

Zero valent iron (Fe0) has been used to remove organic contaminants. However, its low utilization efficiency and high toxicity have hindered its application. In this study, Fe3C@Fe0-loaded biochar (Fe3C@Fe0@BC) with 40.1% Fe content and slight Fe release presented excellent removal efficiency, stability, and reusability for tetracycline hydrochloride (TH). Fe3C@Fe0@BC presented selective oxidation degradation to TH in real wastewater and eliminated 99.1% of TH after a 12 h treatment, which considerably exceeded the removal action of fresh Fe0 and biochar. Radical scavenger experiments, desorption experiments, and electron paramagnetic resonance analysis confirmed that the removal of TH on Fe3C@Fe0@BC was mainly mediated by degradation and the Fe utilization efficiency was high up to 214%. TH degradation pathways and hydroxylation reactive sites were explored using high-performance liquid chromatography-mass spectrometry and density functional theory modeling. The acute toxicity of TH solution after Fe3C@Fe0@BC treatment and that of the fresh or used materials on Daphnia magna was the lowest. Fe/C composites present a good alternative for Fe0 because of the high Fe utilization efficiency and low toxicity of the material and produced antibiotic degradation byproducts. This study presents important findings related to the toxicity of Fe/C composites and provides strong technical support for the practical application of Fe/C composites.