The project that we have elaborated "Descriptive study and automation of the aerators of a treatment plant" The project consists in studying this installation according to two levels: The descriptive study of a treatment plant this study is divided into two parts the pre-treatment consists in removing the coarsest solid pollutants from the waste water it is a simple stage of physical separation, the physico-chemical treatment eliminates the matters in solution in the water (organic matters, mineral substances).And the automation system used (PLC), for the control of the aerators is the aeration programming in order to keep the air mixture with the water continuous without stopping, with very detailed parts on the PLC in general and the chosen PLC in particular, as well as the simulation thatallows the operation of the motors to be obtained.