Key role of hydrodynamic conditions in the adsorption and migration of sulfamethoxazole driven by suspended particulate matter

The widespread use of sulfamethoxazole (SMX) has led to pervasive antibiotic contamination in aquatic environments, where suspended particulate matter (SPM) serves as a critical mediator in the retention, transport, and fate of antibiotic pollutants within riverine ecosystems. However, existing research predominantly emphasizes adsorption mechanisms under static batch equilibrium conditions, overlooking the dynamic interplay between SPM and antibiotics across hydrodynamic conditions regimes.Thus, the dynamic adsorption process of SMX on SPM was investigated through a series of annular flume experiments, and the MIKE 21 model was employed to simulate the migration of SMX and SPM. Results showed that the SMX adsorption amounts decreased significantly with increasing flow velocity, and the SMX desorption would occur when hydrodynamic conditions changed suddenly, especially for the continuous enhancement in velocity. As hydrodynamics stabilized, the re-adsorption of SMX would occur. The adsorption process of SMX was related with the property changes of SPM, and the enhancement of hydrodynamic conditions can significantly weaken the surface complexation between SPM and SMX, further resulting in a decrease in the SMX adsorption amounts. Meanwhile, high flow velocity would cause more obvious pore filling of SMX on SPM and led the clearer SMX adsorption fluctuations under the varying the hydrodynamic conditions. The MIKE 21 simulations identified that the continuous enhanced hydrodynamics significantly prolonged the interaction time between SMX and SPM, while the weak hydrodynamics and high SPM concentrations could particularly slow the SMX diffusion downstream.