RESUMEN
As annual sales of antibiotics continue to rise, the mass of these specially-designed compounds entering municipal wastewater treatment systems has also increased. Of primary concern here is that antibiotics can inhibit growth of specific microorganisms in biological processes of wastewater treatment plants (WWTPs) or in downstream ecosystems. Growth inhibition studies with Escherichia coli demonstrated that solutions containing 1-10 µg/L of fluoroquinolones can inhibit microbial growth. Wastewater samples were collected on a monthly basis from various treatment stages of a 30 million gallon per day WWTP in Maryland, USA. Samples were analyzed for the presence of 11 fluoroquinolone antibiotics. At least one fluoroquinolone was detected in every sample. Ofloxacin and ciprofloxacin exhibited detection frequencies of 100% and 98%, respectively, across all sampling sites. Concentrations of fluoroquinolones in raw wastewater were as high as 1900 ng/L for ciprofloxacin and 600 ng/L for ofloxacin. Difloxacin, enrofloxacin, fleroxacin, moxifloxacin, norfloxacin, and orbifloxacin were also detected at appreciable concentrations of 9-170 ng/L. The total mass concentration of fluoroquinolones in raw wastewater was in the range that inhibited E. coli growth, suggesting that concerns over antibiotic presence in wastewater and wastewater-impacted surface water are valid. The average removal efficiency of fluoroquinolones during wastewater treatment was approximately 65%; furthermore, the removal efficiency for fluoroquinolones was found to be negatively correlated to biochemical oxygen demand removal and positively correlated to phosphorus removal.