A model of tanks-in-series with two types of reactors (rapid reactors and stagnant zones with exchanges between those zones) has been developped to describe the hydrodynamic and mass transfer in waste columns to study the effect of leachate recirculation. The model is compared with a classical tank in series model. Two similar columns (40 kg of dry waste) were equipped with probes inserted at different depths in the waste mass. In the first column, raw leachate was injected during more than 1260 days. On the second column three periods of nitrified leachate recirculation were performed. The first period with raw leachate (150 ml.d-1); the second period with leachate supplemented with KNO3 (same leachate flow-rate and 280 mg N KNO3.d-1); the third period with nitrified leachate (same leachate flow-rate and 61 mg N NO3.d-1). A lithium chloride solution was injected in the two columns to characterize the hydraulic properties of our experimental set-up. In a second step the model was validated with the response of the system on potassium during a second period of leachate supplemented with KNO3 recirculation. The model provides also the response to other compounds such as Cl-.