Materials such as leachate or leachate from hospital waste as a source of contamination and impact on nature and the environment. These juices are sources or vectors of pollution, justifying the purpose of our study. We had carried out three sampling campaigns in 2006, 2008 and 2010, the leachate four hospitals (CUK, HGRK, HGK and HGRN). Thus, we studied the physicochemical parameters in leachates and global settings to the toxicity tests. The results of our study are consistent with each other and show that ecotoxicity is constant for leachate that appear stable while their composition is variable. The toxicity test leachate sorting studied at each hospital establishment. Splits leachate can find a lasting solution in the nano filtration technique membranes during preparation of a wastewater treatment plant in the hospitals studied. Leachate contaminating the surrounding environment if not treated are at their rejection. Thus, instead of using reverse osmosis is an expensive technology and is justified if the standards are drastic, nano filtration is an intermediate way to help avoid pollution of hospital discharges juice. This technique helped us in our study to remove the chemical oxygen demand in the case of CUK. Thus we evaluated the performance of organic and inorganic membranes during the lowering of the inorganic filler according to the speed and pressure that are hydrodynamic conditions. The membranes have a specific behavior with respect to the leachate at the absorption, polarization and clogging of the pores. Indeed, the N01A membrane, discharge of COD is of 70% for a 10 bar pressure. The MP20 has a low membrane adsorption with leachate. The MP-31 provides a high retention rate of COD. There is then a strong membrane-fouling interaction improves the selectivity of the membrane. Leachate particles clog the membrane pores and obstruction and static adsorption increase membrane rejection rate. We studied the coagulation mechanism as a pretreatment to improve the membrane performance on the N01A. On this membrane COD reduction from 70 to 77%, the flux increases to 105 l. h-1.m-2 at a pressure of 10 bar for a COD concentration of 300 mg02l-1. The other two MP-31 membranes and MP20 provides for a flow limit of 11 l. h-1.m-2 COD respectively 1457 mg02l-1on MP-31 MP20 and a concentration of COD 1417 mg02l-1. For a max flow of 13 l.h-1.m-2 the retention percentage is 70% for COD 960 mg02l-1 After coagulation, fouling index was 4.8 for the raw leachate and increases to 4.5 with the supernatant.