Removal of tetracycline by aerobic granular sludge from marine aquaculture wastewater: A molecular dynamics investigation

[Display omitted] •Tetracycline was primarily transported to the cell membrane via electrostatic force.•Aromatic ring and/or amino group were the adsorption sites on tetracycline surface.•Free energy driving tetracycline to the cell membrane was reduced by 30% in seawater.•Sodium ions competed with tetracycline for adsorption sites on the cell membrane. Although biological treatment of marine aquaculture wastewater is promising, the fundamental principles driving the adsorption of tetracycline to microbial cell membrane are not well understood. Using a combination of experiments and molecular dynamics (MD) simulations, the mechanism underlying the biological removal of tetracycline from seawater was investigated. More than 90% tetracycline removal was achieved in an aerobic granular sludge system, with degradation accounting for 30% of total removal. A model of the tetracycline-dipalmitoylphosphatidylcholine lipid bilayers was established to elucidate the transport mechanism of tetracycline from bulk solution to microorganisms’ cell membrane. 62% of the driving force for tetracycline adsorption on the cell membrane originated from electrostatic attraction. The electrophilic groups on tetracycline (amino and aromatic groups) were attracted to the phosphate groups in the cell membrane. Sodium ions, which are abundant in seawater, decreased the interaction energy between tetracycline and the cell membrane.