The most significant parameters of a model that simulates the hydraulic and biological behaviour of a sanitary landfill were determined. These parameters were particulate matter, hydrolysis constant, initial waste polluting potential, and waste porosity. Based on experimental data collected from two reactors, the acidogenic stage was characterized. There was an inhibition due to the accumulation of VFA in the reactor fed with a higher than usual content of easily biodegradable matter. In such reactors the methanogenic stage was never reached. The COD and VFA curves of the reactor where the methanogenic stage was attained, showed a maximum around the 200th day. After 500 days, a noticeable methane production started. Based on first order kinetics, the value of the particulate matter hydrolysis constant was determined to be 0.8×10−3d−1.