Adsorption and migration of sulfamethoxazole driven by suspended particulate matter in water body

The extensive use of antibiotics has led to significant antibiotic pollution in water bodies, and suspended particulate matter (SPM) is known to be a key carrier of antibiotics in rivers. In this work, the adsorption characteristics of sulfamethoxazole (SMX) on SPM was investigated through batch adsorption and annular flume experiments, and the MIKE 21 model was employed to simulate the migration of SMX and SPM. Results revealed that most SMX adsorption occurred rapidly within 20 min, and 80 % of the equilibrium adsorption capacity was reached. Multilayer adsorption was confirmed by Freundlich model, and adsorption process was found to be spontaneous, endothermic, disordered, and the equilibrium adsorption amounts of SMX on SPM increased with salinity and organic matter increase. SMX desorption from SPM occurred upon the sudden changes of hydrodynamic states, nearly reaching the one-fifth of the SMX equilibrium adsorption amounts within 30 min and the re-adsorption of SMX on SPM would occur with water remained stationary or the re-disturbance time prolonged. The dynamic adsorption process of SMX related with the physicochemical property changes of SPM, which was contributed to the hydrogen bonds, π–π interactions, surface complexation, significantly influenced by the pore filling at the macropore and mesopore scales. The MIKE 21 simulations confirmed hydrodynamic states as the primary factors affecting the migration of SMX and SPM. SMX concentrations in the water would decrease in the presence of SPM, leading to the slower downstream migration of SMX.