Adsorption mitigated aggregation controls sedimentation of sulfonamide antibiotics in complex with dissolved black carbon.

Dissolved black carbon (DBC) is widely present in aquatic environments and influences pollutant behavior. Herein, sulfonamide antibiotics (SAs) were used to investigate their adsorption onto DBC and the aggregation and sedimentation of SA-DBC complexes. The results showed that adsorption of SAs onto DBC initiated stabilization of DBC/SA-DBC aggregation, with SM2-DBC displaying the strongest stabilizing capacity, which was closely associated with SA-DBC sedimentation. Adsorption capacity was SM2 > SD > SMX at circumneutral pH, with stronger SM2-DBC interactions increasing complex stability. This adsorption stabilized DBC through enhanced electrical double-layer (EDL) interactions, combined with possible non-DLVO mechanisms (e.g., hydration repulsion and steric hindrance), increasing CCCNa from 44 to 115, 136, 107 mM and CCCCa from 1.75 to 2.08, 2.39, 2.00 mM for SD, SM2, SMX, with SM2-DBC showing the greatest CCC. Moreover, high ionic strength in natural water promoted DBC aggregation. The sedimentation experiments revealed that DBC-mediated SAs transport was time/ionic strength dependent, with SM2 exhibiting minimum deep-water partitioning (54%, 72 h) under hydrostatic conditions. The sedimentation of SA-DBC remains inhibited by adsorption/aggregation (p < 0.05) under adjusted environmental conditions. This stabilization mechanism implied that the adsorption of anionic pollutants onto DBC can stabilize contaminant-DBC aggregation and suppress sedimentation under prolonged environmental timescales. These findings elucidate the coupled behaviors of DBC and SAs in diverse aquatic conditions, emphasizing the potential role of DBC in regulating pollutant behaviors.