The potential value of zeolitic materials (ZM) obtained from a hazardous waste, Such as coal fly ash, for the retention of NH4+ present in liquid effluents from a Sewage Treatment Plant (STP) is studied. A wastewater sample was taken from an STP in Zaragoza (Spain) after conventional treatment at the Plant. The water was treated with different amounts of three ZM: NaP1 zeolite, K-F zeolite and K-Chabazite/K-Phillipsite zeolites all of them in powdered and granulated state. The wastewater was treated by two kinds of processes: continuous stirring batch experiments with powdered ZM, and fixed packed bed of granulated ZM in a column. The powdered materials reduced about 80% of NH4+ from wastewater, even in the presence of Ca2+, which competes with NH4+ for the cation exchange sites in zeolites. Around 70% of NH4+ reduction was achieved with granulated materials. In both cases, moderate ZM/wastewater ratios had to be used to achieve those results, with K-zeolites slightly less effective in NH4+ retention. (C) 2008 Elsevier B.V. All rights reserved.