Effectiveness of aluminum-based drinking water treatment residuals as a novel sorbent to remove tetracyclines from aqueous medium

Low levels of various veterinary antibiotics (VAs) have been found in water resources across the United States as a result of nonpointsource pollution. As the first phase of developing a potential green sorbent for tetracycline (TTC) and oxytetracycline (OTC), we examined the effects of solution chemistry, pH, ionic strength (IS), sorbate:sorbent ratio (SSR), and reaction time on TTC and OTC sorption by a waste byproduct of the drinking-water treatment process, namely, Al-based drinking-water treatment residuals (Al- WTR). The sorption of TTC and OTC on Al-WTR increased with increasing pH up to pH 7 and decreased in the pH range of 8 to 11. A concentration of 20 g L^-1 was deemed as optimum SSR, where more than 95% of the initially added TTC and OTC were sorbed and equilibrium was reached in 2 h. A pseudo-second-order model (R² = 0.99) was used for Al-WTR sorption for TTC and OTC. The data best fit the linearized form of the Freundlich isotherm (R² = 0.98). No significant effect (p > 0.05) of IS on sorption of TTC and OTC was observed between 0.05 and 0.5 mmol L^-1. However, at higher initial concentrations (>1 mmol L^-1), IS dependence on TTC and OTC sorption was observed. Surface complexation modeling and Fourier transform infrared spectroscopy analysis indicated the possibility of TTC and OTC forming a mononuclear monodentate surface complex through strong innersphere-type bonds on Al-WTR. The results show promising potential of Al- WTR for use as a "green" and cost-effective sorbent to immobilize and stabilize TTC in soils and waters.