Sewage sludge produced in wastewater treatment plants represent a significant portion of waste resulting from human activity and it is important to offer new ways of treatment. Thermal gasification of sludge is a promising thermal treatment, particularly because it can lead to a recovery of energy and a drastic reduction in the initial waste volume. However, it is a subject that has rarely been treated in the literature for sewage sludge. In particular, the nitrogen compounds present in significant quantities in the sewage sludge and their reactions during a thermal gasification step, must necessarily be taken into account. In order to study nitrogen behavior, this paper presents experimental results that are included in a model to predict NH3 emission.