Sorption of Oxytetracycline On Drinking Water Treatment Residuals: Preliminary Results.

Veterinary antibiotics (VAs) have recently been detected at relatively high concentrations in soils, surface waters, and ground-waters. Tetracycline antibiotics (TCs) (tetracycline, oxytetracycline (OTC), and chlorotetracycline), rank second in production and usage worldwide, are among the most commonly used VAs in the livestock industry, with OTC being the most popular in the US. Studies have shown that TCs are poorly adsorbed in the gut of animals and a high proportion (25-75%) is excreted unchanged in feces and urine, which can enter into soils, surface-and/or ground-water via manure applied soils or manure-storage at CAFOs. Thus, effective means of immobilizing TCs in soils need to be employed to reduce the potential health hazards that could result from the presence of TCs in the soil environment, and consequently in surface-water bodies. Studies have shown the ability of Al and Fe hydrous-oxides to form strong complexes and retain TCs, thereby decreasing its mobility. We have identified an inexpensive source of Fe/Al hydro(oxides) in the form of drinking-water treatment residuals (WTRs) that can be potentially utilized to immobilize and stabilize TCs in manure and TC-enriched manure-amended soils. This study examined the adsorption and desorption characteristics of OTC in Fe/Al-WTRs. All adsorption experiments were carried out in batch-mode, and OTC-adsorption on WTRs was investigated as a function of solid/solution ratio (1:5, 1:10, and 1:25), equilibration time (5 min - 48 hr), pH (4 - 10), ionic strength (0.05- 0.5 M) and initial OTC load (0.05-5 mM OTC L^-1). The above parameters were varied one at a time to study their effect on the OTC-adsorption process. Isotherm modeling was performed and desorption studies were carried out immediately after each adsorption step. Preliminary results show that Fe-WTR and Al-WTR have high OTC adsorption capacity.