Removal of chlortetracycline from water by Bacillus cereus immobilized on Chinese medicine residues biochar

Biochar-immobilized microorganism technology is an effective way to remove antibiotic contamination from water bodies. In this study, three common Chinese medicine residues (forsythia, erding and honeysuckle) were selected as raw materials for pyrolysis at different temperatures. The biochar obtained was used as a carrier to immobilize the highly efficient chlortetracycline-degrading bacterium Bacillus cereus LZ01 and analyze the complex’s removal characteristics and removal mechanism chlortetracycline. The results showed that the Chinese medicine residue biochar pyrolyzed at 500 °C had a higher removal capacity for chlortetracycline and could adsorb more microorganisms. The erding medicine residue biochar (EBC-500) pyrolyzed at 500 °C possessed a more developed pore structure and suitable nutrients. And the alkalinity of EBC-500 had the effect of relieving the inhibition of bacteria by acid, providing more suitable living conditions for the growth of bacteria, and improving the removal of chlortetracycline. Orthogonal experiments determined the optimal conditions for microbial immobilization by biochar: 10% microbial inoculum, 0.5 g biochar dosage, 0.097 - 0.15 mm biochar particle size, and 36 h immobilization time. The FT-IR spectra showed that the complex integrated all functional groups of biochar and degrading bacteria. The comparison of the removal effect before and after inactivation revealed that the removal mechanism of chlortetracycline in water by the complex was mainly determined by a combination of microbial degradation and biochar surface adsorption. This study provides a method for preparing an efficient biochar–microbial complex using Chinese medicine residue waste substrate, which provides a new idea for removing chlortetracycline from water.