UV-C-driven oxidation of ciprofloxacin in conventionally treated urban wastewater: degradation kinetics, ecotoxicity and phytotoxicity assessment and inactivation of ciprofloxacin-resistant Escherichia coli

BACKGROUND: This study aims at evaluating the degradation of the antibiotic ciprofloxacin (CIP) in urban wastewater effluents using a UV-C-driven oxidation processes in the presence of hydrogen peroxide. Under the optimum experimental conditions, the phytotoxicity and ecotoxicity of the treated samples were investigated against one plant species (Sinapis alba) and a crustacean (Daphnia magna), respectively. The efficiency of the process to remove E. coli and ciprofloxacin-resistant E. coli was also assessed. RESULTS: Complete degradation of CIP was achieved within 15 min of treatment under the optimum concentration of the oxidant ([H₂O₂] = 10 mg L⁻¹). The degradation rate of the antibiotic fitted pseudo-first-order kinetics. An increase in both shoot inhibition and root inhibition was observed, until 60 min of treatment, beyond which, the phytotoxic effect was eliminated. The results demonstrated the ability of the UV-C process to reduce the toxicity towards D. magna by 40%, comparatively, to the untreated wastewater. The inactivation of E. coli and CIP-resistant E. coli was achieved within 2 min of treatment. CONCLUSIONS: The UV-C/H₂O₂ process was successfully applied for the removal of CIP at low environmental concentration level. The treatment process was able to achieve a significant reduction of phyto- and eco-toxic effects, as well as E. coli harbouring resistance to CIP.