Interaction between chlortetracycline and calcium-rich biochar: Enhanced removal by adsorption coupled with flocculation

A high residual concentration of antibiotics in the environment represents a to the animal and human health, thus, removal of these antibiotics is an urgent problem in need of a solution. In this study, calcium-rich biochar (CRB) pyrolyzed from a natural organic-inorganic-composite (i.e., crab shell) was investigated for its significant efficiency in removing efficiency of chlortetracycline (CTC) from aqueous solution. Batch experiments were conducted to explore the interaction between CRB and CTC to characterize the ability of CRB to remove CTC. Results showed that the equilibrium pH of the system decreased as the initial concentration of CTC increased, resulting in a complicated CTC removal process. Specifically, at a low initial concentration of CTC, the predominantly occurred through adsorption, which is well-described by the Freundlich isotherm model. The adsorption capacity of CRB for CTC reached 1432.3 mg g(-1) at 298 K. Adsorption rates were estimated by kinetic models, and the pseudo-second-order model displays a good fit for the kinetic data at various concentrations. Adsorption and flocculation were responsible for the removal of CTC at a high initial concentration. The maximum removal capacity was 5048 mg g(-1) at 298 K. Microcosmic characterization and macroscopic results demonstrated that cation bridging, p-p interaction, electrostatic interaction and hydrogen bonding could be involved in the removal process, which varied with the initial concentration of CTC. Therefore, based on the high-efficiency and low-cost of CRB, this material promises to be an ideal candidate to remove antibiotics (e.g., CTC) from wastewater and control their transport within the environment.