ALUMINUM-BASED DRINKING-WATER TREATMENT RESIDUALS A “GREEN” SORBENT FOR TETRACYCLINES

As the first phase of developing a potential green remediation approach for tetracyclines (TCs), we examined the effects of solution chemistry - pH (3-11), ionic strength (IS) (0.01-0.5M KCl), sorbate: sorbent ratio (SSR) (5-100 g L^-1), and reaction time (0.16-96 h) - on tetracycline (TTC) and oxytetracycline (OTC) sorption by a waste byproduct of the drinking-water treatment process, namely, aluminum-based drinking-water treatment residuals (Al-WTRs) as a function of initial TTC and OTC concentrations (0.05-2.0 mM TTC/OTC L^-1). The effect of competing ligands, phosphate-P(V) and sulfate, and complexing metal (calcium) on TTC and OTC sorption was also evaluated. Sorption of TTC and OTC on Al-WTR increased with increasing pH up to pH 7, above which it started decreasing in the range of pH 8 to 11. A concentration of 20 g L^-1 was deemed as optimum SSR for Al-WTR where more than 95% of the TTC/OTC was sorbed and equilibrium was reached in 2h. The reaction kinetics data best fit second order model (r²=0.99) for both TTC and OTC. Sorption isotherms were plotted to evaluate the effect of IS on TTC/OTC sorption. Best data fits were obtained using the linearized form of the Freundlich isotherm (r²=0.99). No significant effect (p>0.05) of IS on sorption of TTC/OTC was observed between 0.05-0.5 mM. However, at higher initial concentration (>1 mM), IS dependence of TTC sorption was observed. Sorption of TTC/OTC by Al-WTR decreased in the presence of P(V), also exhibiting strong pH dependence. Addition of sulfate did not influence TTC/OTC sorption on Al-WTR. A cooperative effect of calcium on TTC/OTC sorption was observed at alkaline pH. Our research is expected to help develop a “green” remediation technique to immobilize and stabilize TCs in manure and manure-amended soils, and also provide a cost-effective medium for TCs immobilization in wastewater treatment facilities.