Peroxydisulfate activation by one-step pyrolysis iron-rich sludge biochar for tetracycline removal in water: performance, mechanism and degradation pathway

Abstract Steel sludge, a byproduct generated from wastewater treatment in the steel industry, has high levels of iron salts and heavy metals, while traditional treatment technologies such as land application, sanitary landfilling, and incineration make resource recovery and utilization challenging. In this study, iron-rich sludge biochar (FSB) was prepared by one-step pyrolysis of iron-rich sludge generated from a steel factory and utilized to activate peroxydisulfate (PS) for tetracycline (TC) removal. Results showed that FSB pyrolyzed at 450 ºC (FSB450) exhibited excellent degradation performance under the optimal conditions (FSB450 dosage of 0.4 g L −1 , initial solution pH of 3, and PS dosage of 8 mM). In the FSB450/PS system, oxygen-containing functional groups, edge defects, and inherent iron oxides in FSB provided abundant active sites that can facilitate the generation of reactive oxygen species (ROS), including SO 4 ˙ − , . OH, O 2 ˙ − , and 1 O 2 , thus accelerating TC degradation by both radical and non-radical processes. Combining with density functional theory (DFT) calculations, the degradation pathways of TC may include demethylation, decarbonylation, dealkylation, dehydroxylation, etc. Meanwhile, the overall toxicity of TC intermediates was reduced after FSB450/PS treatment. Overall, this study provides a novel and feasible approach for the resource utilization of iron-enrich sludge and the treatment of TC wastewater treatment.