Characteristics of tetracycline adsorption by different embedded biochar materials

This study explored six novel biochar composite materials for adsorbing tetracycline antibiotics adsorption. These materials-namely, Bauhinia biochar, Bauhinia magnetic biochar, rice straw biochar, rice straw magnetic biochar, rice straw hydrothermal biochar, and rice straw hydrothermal magnetic biochar, were encapsulated with sodium alginate to form adsorption spheres. Results showed that magnetic biochar materials had higher adsorption capacities than non-magnetic ones, with rice straw magnetic biochar adsorption spheres showing the highest capacity at 3 mg/g. The isothermal adsorption of tetracycline by rice straw magnetic biochar adsorption spheres followed the Freundlich model, while the adsorption kinetics were best described by the pseudo-second-order model. The adsorption half-life was 3 h, and factors including biochar dosage, temperature, pH, and salinity affected the removal rate. SEM and FTIR analyses of rice straw hydrothermal magnetic biochar, rice straw magnetic biochar, and rice straw biochar revealed that rice straw biochar materials had a microporous structure mainly composed of C and O, while magnetic materials also contained significant amounts of iron. All three materials contained hydroxyl, alkene, alkyne, and alkyl functional groups. The increased FeO bonds in magnetic materials were the primary reason for the enhanced adsorption performance. Moreover, rice straw magnetic biochar adsorption spheres showed good reusability for high-concentration tetracycline. For low-concentration tetracycline, the adsorption capacity recovery exceeded 60 %, achieving an overall removal rate of over 80 %. Owing to their excellent recyclability and rapid adsorption rates, the rice straw magnetic biochar adsorption spheres hold significant potential in advanced wastewater treatment containing tetracycline antibiotics.