The aim of this study is to decrease the biological oxygen demand (BOD5), chemical oxygen demand (COD) and total Suspended solids (SS) of urban wastewater by activated sludge. To begin with, we need to focus on determining the best activated sludge pilot plant operating conditions in order to confirm the performance of the station and a long period of the pilot purification test has been carried out. The pilot operating conditions correspond in terms of mass load to a low load are: Flow 0.5 l/h; Oxygenation rate 60%; 100% recycling of the activated sludge; Aeration tank agitation 100 rev/min. Also, a sustained performance during the trial period, during which, the station operated in low mass load, producing water with BOD5, COD and SS, which is respectively (90.20%, 89. 79% and 97.67%) much lower levels in Moroccan discharge standards.