Removal performance and mechanism of tetracycline from water bodies by novel iron-manganese modified biochar foam concrete

The widespread use of tetracycline has resulted in elevated antibiotic concentrations in natural water bodies， posing significant threats to aquatic ecosystems and public health. Although iron-manganese modified biochar （IMBC） can effectively remove tetracycline， its powdered form is prone to leaching during application， leading to reduced utilization efficiency and potential system clogging. In this study， foam concrete （FC） was employed as an immobilization matrix to fabricate a novel iron-manganese modified biochar foam concrete （IMBC-FC） composite. The results showed that sufficient hydration reactions occurred during the immobilization process， endowing IMBC-FC with a highly porous structure that effectively avoided the masking of active sites on IMBC. The tetracycline removal efficiency of IMBC-FC reached 87.7%， and the impact of immobilization on the removal performance of IMBC was less than 10%. Removal pathway analysis indicated that oxidative degradation contributed approximately 56.9% to tetracycline removal， and singlet oxygen （¹O₂） was identified as the dominant reactive oxygen species （ROS） in the system. Functional groups such as hydroxyl （—OH） and carboxyl （—COO⁻） generated during hydration likely participated in both ROS generation and electron transfer， thus synergistically facilitating the degradation process. Furthermore， a comprehensive evaluation of the engineering application performance of IMBC-FC was carried out in accordance with relevant standards for water treatment filter media and constructed wetland substrates. The results demonstrated that IMBC-FC exhibits excellent advantages in porosity， mechanical strength， and tetracycline removal efficiency， indicating its promising engineering application prospects. This study is expected to provide a reliable technical pathway and theoretical support for the efficient immobilization of metal-modified biochar.