The purpose of this project was the design / construction, pre-start and start-up of the Sousa WWTP. The treatment scheme for this WWTP is based on a biological wastewater treatment with activated-sludge process operated in a conventional aeration system, carried out through two bioreactors with the configuration of an oxidation ditch. There are two treatment phases: liquid phase and solid phase. The main data for the WWTP, for the project horizon, was: equivalent population of 90,000 inhabitants and average flow of 13,855 m3 / day.