Kinetics of ciprofloxacin degradation by ozonation : effects of natural organic matter, the carbonate system, and pH
The presence of pharmacologically active and persistent compounds in drinking water sources is an environmental and public health concern. Sources of pharmaceuticals in the aquatic environment include wastewater treatment plant effluents and veterinary use. Antibiotics are of special concern because of their role in the spread of bacterial resistance. Conventional drinking water treatment processes are often ineffective for removing trace organic contaminants. Ozonation processes have demonstrated the ability to remove pharmaceutical compounds from drinking water supplies. During the ozonation of drinking water, the primary oxidants are ozone and hydroxyl radicals formed during the decomposition of ozone. Both oxidants contribute to the removal of pharmaceutical compounds; however, the relative rates of destruction by these two oxidants depends on the treatment operating conditions, the background water chemistry and the structure and reactivity of the target compound. This study investigated the relative impact of natural water characteristics, such as pH, the carbonate system, and natural organic matter, on the removal of the fluoroquinolone antibiotic ciprofloxacin by ozonation processes. Rate constants for k"O3, Cip obtained at pH 7 were approximately one order of magnitude higher than at pH 5 because ciprofloxacin changes from a positively charged cation to a neutral species over this pH range. The results showed that there was very little variation of the rate constants for ciprofloxacin oxidation by O₃ or hydroxyl radicals regardless of the carbonate concentration or the presence of the two organic matters studied in this research. Typical values for k"O3, Cip and k"HO°, Cip obtained at pH 7 ranged between 1.49x10⁴ and 1.64x10⁴ M⁻¹s⁻¹ and 1.29x10¹⁰ to 1.80x10¹⁰ M⁻¹s⁻¹, respectively. However, the presence of carbonate and other hydroxyl radical scavengers did have an impact on O₃ and hydroxyl radical exposure. The relative impact of these two oxidants changed depending on the pH of the system and the presence of carbonate and natural organic matter.