Ciprofloxacin ozonation in hospital wastewater treatment plant effluent: Effect of pH and H2O2

The ozonation of ciprofloxacin was studied in hospital wastewater treatment plant effluent with focus on parent compound degradation, degradation product identification and residual antibacterial activity. Before ozonation, ciprofloxacin sorption on suspended solids was tested as a function of temperature (10.0–27.5 °C) and pH (3, 7 and 10). Temperature did not significantly affect ciprofloxacin sorption while sorption was highest at pH 7 (log Kd = 4.7) compared to pH 3 (log Kd = 4.3) and 10 (log Kd = 3.9) (n = 3). Ozonation was slowest at pH 7 with ciprofloxacin half life times of 29 min, compared to 19 and 27 min at pH 10 and 3, respectively. Addition of 10–1000 μM H2O2 increased ciprofloxacin half life times up to 38 min, probably influenced by competition with H2O2 for ozone as well as radical species. Ciprofloxacin ozonation products were identical as previously detected during ciprofloxacin ozonation in deionized water and revealed strong pH dependence. Residual antibacterial activity was measured by agar diffusion tests. For Pseudomonas fluorescens and Escherichia coli, reduction of antibacterial activity was related to the parent compound degradation, while degradation products indicated to be the main compounds with respect to the antibacterial activity against Bacillus coagulans.