This paper concerns the removal of ammonium ions from wastewater using a naturally occurring zeolite from Dogantepe region in Turkey. Both batch and continuous (column) experiments were carried out. In batch studies, effects of stirring time (5-120 min) and initial ammonium concentration (8.8-885 mg NH4+-N1(-1)) on removal efficiency and adsorption isotherms were investigated. In column studies, effects of flowrate, pH, initial ammonium concentration, washing with acid and regeneration on the ammonium adsorption capacity of the zeolite were determined. Increasing initial ammonium nitrogen concentration from 5.0 to 12.0 mg l(-1), increased the exchange capacity from 0.70 to 1.08 mg NH4+-N g(-1). The flowrate and pH values, at which the highest adsorption capacities were obtained, were found to be 0.5 ml min(-1) (0.87 mg NH4+-N g(-1) zeolite) and 4 (mg NH4-N l(-1)), respectively. The corresponding values after washing with acid and regeneration were determined to be 1.32 and 0.73 mg NH4+-N g(-1), respectively. The cation exchange capacity of Dogantepe zeolite was found to be 164.62 meq. per 100 g. These findings show that Dogantepe zeolite can be used for the removal of ammonium from wastewater. (C) 2004 Elsevier B.V. All rights reserved.