The supernatant effluent from full scale anaerobic codigestion of waste activated sludge and the organic fraction of municipal solid waste was treated by a demonstration sequencing batch reactor for short-cut nitrogen removal After inoculation with conventional municipal activated sludge, the strategy of two stage start up allowed us the fast speciation of ammonia oxidizing bacteria : (achieved within 20 days), then the achievement of the rmaximal treatment potential. (0.8 kgN m(-3) d(-1)) for nitritation-denitritation. By automatic indirect control of the free ammonia and the free nitrous acid concentrations, the via nitrite Pathway was fully and stably achieved Under aerobic. conditions (DO of 1.5 mg L-1) and T of 15 degrees C. Under:ordinarii: operation, the specific nitritation rates were 15-20 mgN gMLVSS(-1)h(-1), while the denitritation rate was 45-50 mgN gMLVSS(-1)h(-1). In situ and ex situ respirometry and gene based molecular techniques demonstrated the stable presence of a dominant, restricted ammonia oxidizing bacterial population After the first stage aerobic start-up. We therefore demonstrated that codigestion and advanced nitrogen removal from anaerobic supernatant may optimize the performances of an integrated municipal treatment plant.