The adsorption of enrofloxacin, a veterinary antibiotic onto natural zeolite and further decontamination of zeolite was investigated in the present study. In the first part of the study, the effects of pH, temperature, and presence of ammonium ion on the adsorption process were examined and evaluated on the basis of Langmuir and Freundlich isotherms. Adsorption of enrofloxacin on natural zeolite was found to be highly pH dependent, exhibiting increases correspondent to decreases in pH. The positive value of enthalpy change showed the endothermic nature of adsorption processes. The presence of ammonium ion enhanced the adsorption of enrofloxacin. In the second part of the study, infrared (IR) spectroscopy, and scanning electron microscopy (SEM) were used for the determination of the modifications on the zeolite surfaces resulting from adsorption and ozone treatment. It was found that ozone at sufficient concentrations over specified time periods was able to decompose the enrofloxacin adsorbed on zeolite. (c) 2005 Elsevier B.V. All rights reserved.