Nitrified leachate recirculation represents a promising strategy for a more sustainable landfill management. The objective of this research was to determine reactions involved in nitrate reduction in laboratory scale batch tests. Three control reactors without nitrate addition showed a classical and good reproducible behavior with acidogenic and methanogenic phases during the 200 days of experiment. In two test reactors, nitrate was added (250 mg N-NO3-/L) at various moments (Day 3, 17, 45 and 143) of the waste degradation process. We concluded that: (1) Variations of the N2O/N2 ratio were small when the organic carbon concentration was not limiting. (2) N2 was consumed after denitrification. The possibility of a nitrogen fixation reaction in the presence of NH4+ is discussed. (3) H2S concentration seems to control the nitrate reduction pathway: above a certain threshold of H2S, Dissimilatory Nitrate Reduction to Ammonium (DNRA) replace denitrification. Nitrified leachate recirculation during acidogenesis should be avoided because of higher H2S production which could induce DNRA.