Kinetic studies of nitrification and denitrification were carried out on reconstituted cores of sediments taken from wastewater stabilization ponds. This study aims to quantify the nitrification and denitrification in the sediment and to offer kinetic models to describe the processes. Sediment cores were collected, and laboratory studies were performed. The result showed that nitrification and denitrification processes are absent in the water column of stabilization ponds of the Bertrix (Belgium) wastewater treatment plant. On the contrary, nitrification and denitrification rates measured on 18 cores of sediment are, respectively, in the range of 0.12-1.56 g N-NH 4 + /m 2 day and 0.1-1.2 g N/m 2 day. In order to describe nitrification and denitrification processes, two kinetic models were developed using the Monod standard equation.