Abstract: In this study, photocatalytic degradation of ciprofloxacin (CIP) was investigated. CIP is a widely used quinolone antibiotic. Removal of CIP in the dark is negligible. The removal efficiency by photolysis of CIP was 25.3%. The removal efficiencies after 30 min irradiation were 85%, 93.5% and 97% at pH values 3, 6 and 9 in the presence of 0.5 g/L TiO2, respectively. Modified form of the Langmuir-Hinshelwood equation has been successful as a quantitive model to describe solid-liquid interactions. Kinetic constant k is reactivity constant, K is the adsorption equilibrium constant and kap (kK) is the apparent first order reaction constant, these were determined as 0.673 mg/L min, 0.662 L/mg and 0.445 (1/min), respectively. The results showed that after 30 min irradiation of CIP, solution was degraded 95%, whereas COD removed was 40.3%. The enhancement of biodegradability, evaluation in terms of the BOD5/COD ratio, increased from 0.043 to 0.403. This increase is not sufficient for treatment in conventional activated sludge unit. Additionally, the biodegradability of CIP photo-transformation products was assessed by BOD test. k (1/d), BOD reaction rate constants were determined as 0.0857 (1/d) and 0.1778 (1/d) for untreated and treated CIP solution, respectively.
