In comparison to a single‐stage deammonification system, large differences of N2O emissions in double stage treatment with nitrification have been documented. Experiences are presented from pilot‐scale nitrification plants employing continuous feeding and clarification as well as sequencing‐batch reactor systems. During treatment of digestion centrate with high NH4‐N concentrations, nitrous oxide gas was identified in reactors and exhaust gases. With similar NH4 reduction, the results revealed an order of a magnitude lower N2O emissions during wastewater treatment in a single‐stage deammonification system.