(602ad) Ozone Treatment of Tetracycline Antibiotics: Transformation Kinetics and Removal in Water/Wastewater Matrices

Abstract by Zachary Hopkins researching under Dr. Lee Blaney

The fate of pharmaceuticals in the environment is of increasing concern.  Antibiotics represent unique threats to human and ecological health due to the potential for development of antibiotic resistance, inhibition of select microorganism populations, and various sub-lethal effects stemming from the ability of antibiotics to act as intermicrobial signaling agents.  To preclude lasting effects to environmental and human health, advanced water and wastewater treatment processes are required to successfully remove trace concentrations of antibiotics from water supplies.

In this research, three tetracycline antibiotics (i.e., tetracycline, chlortetracycline, and rolitetracycline) were treated using concentrated aqueous ozone solutions (~16 mg/L as O₃), which were generated by bubbling gaseous ozone into DI water.  The baseline structure of tetracycline antibiotics contains four potential sites for ozone interaction.  All three tetracyclines have pK_a values of approximately 3.3, 7.6, and 9.3; above pK_a,2, ozone reacts rapidly with the free tertiary amine functionality (~4×10⁶ M^-1s^-1).  Below pH 7.6, ozone reacts with the tetracycline ring structure.  Regardless of pH, ozone was extremely reactive with the three tetracyclines; for example, the apparent second order rate constants ranged from 5×10⁴ to 5×10⁶ M^-1s^-1 across the pH range of interest (i.e., pH 5–9).  Tetracyclines were measured using ultrahigh performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS).

While pH affects the reaction kinetics of tetracycline transformation by ozone, a variety of water quality parameters, including alkalinity and natural organic matter (NOM), influence the ultimate transformation of tetracyclines in water/wastewater treatment.  To draw general conclusions about the impacts of the background water quality on ozonation of the three tetracyclines of concern, three different water matrices, namely tap water, surface water from Herbert Run (Baltimore, MD), and tertiary effluent from the Little Patuxent Water Reclamation Plant (Savage, MD), were employed.  These three experimental solutions were chosen to resemble treatment of finished drinking water, raw drinking water, and treated wastewater.  Tetracyclines (approximately, 2×10^-9 to 2×10^-7 M) were spiked into these background matrices and dosed with ozone (approximately, 3×10^-4 M) to result in molar ratios of applied ozone to initial (total) tetracycline antibiotics of 0–5 mol/mol.  The ultimate transformation of the three tetracycline antibiotics in these matrices will be presented as a function of pH, NOM content (measured as total organic carbon), and alkalinity.  This data will be beneficial to the design of ozonation processes aimed at treating trace concentrations of pharmaceuticals in water/wastewater treatment processes.