Utilizing preferential ion exchange of zeolite to ammonium, the conventional contact stabilization activated sludge process (CS) can be upgraded to a new type nitrogen removal process, zeolite enhanced contact-adsorption regeneration-stabilization process (M). For municipal wastewater, the effluent ammonium concentration of the ZCS process was around 6.83 mg/L, indicating that ammonium removal efficiency was enhanced over 27% when the influent ammonium concentration was between 24.7 and 50.5 mg/L in the same hydraulic retention time (HRT) and sludge retention time (SRT) conditions as those of the CS process. The results of PCR-DGGE technology showed that the microbial diversity, uniformity and abundance of the ZCS process were all higher than that of the CS process. In addition, anoxic/oxic (A/O) process with the volumetric ratio of oxic tank to anoxic tank being 2: 1 was preferred for the regeneration process. The pilot scale ZCS process with the capacity to treat up to 72 m(3)/d of municipal wastewater was also monitored. The test results revealed that ammonium saturated zeolite could be biologically regenerated effectively and in time. The daily zeolite powder addition was limited to the amount that made up the loss due to the sludge excluding. Furthermore, the orthogonal experiments results showed that the most significant effects on nitrogen and ammonium removal were zeolite powder dose and external recycle ratio, respectively. (C) 2007 Elsevier B.V. All rights reserved.