In this study, a nitrification/denitrification process via nitrites has been developed in a laboratory-scale sequencing batch reactor (SBR) operating at 32 degrees C with a cycle length of 8 h to treat real reject water from the anaerobic digestion of sewage sludge (700-800 NH4(+)-N mg L-1). Because of the lack of biodegradable organic matter in the tested wastewater, the denitrification process requires the addition of an external carbon source as an electron donor, such as methanol, which increases the process cost. To avoid this charge, sulfides, which would come from the anaerobic sludge digestion process, could be used to develop the autotrophic denitrification in the SBR. Biological nitrogen removal (BNR), using HS- for denitrification in a laboratory-scale SBR, worked well, using a hydraulic retention time of similar to 1 day, a sludge age of 30 days, and an average biomass concentration of 1.75 g of volatile suspended solids (VSS) per liter (g VSS L-1). Two internal aerobic/ anoxic periods were used to control the pH within a range of 7.3-8.5, and the dissolved oxygen (DO) concentration was maintained at <1 mg/L to promote the nitrite route. Sodium sulfide hydrate was used as the synthetic source for autotrophic denitrification.