The treatment of wastewater is now an important issue for the quality of the environment and the quality of the water resource. The transport of wastewater through the pipes of a sanitation network, also known as “collectors,” is generally done by gravity, but can sometimes be carried out by pumping, under pressure or under vacuum through pumping processes and lifting stations. To protect the network against clogging and corrosion, a pretreatment including screening, sieving, desanding, and degreasing is carried out before the discharge of water into the separate or combined sanitation network. The regulation of the flow of wastewater and rainwater, in the case of a combined network, is ensured by equipment designed to temporarily keep significant and sudden water inflows, in order to not disrupt the proper functioning of the treatment plants and to limit the risk of flooding. It is therefore recommended and possible to significantly increase the capacity of wastewater treatment plants by optimizing them to primarily improve the quality of the treated effluent and reduce the operating costs of these facilities. This current state-of-the-art rule summarizes how to approach optimizing the operation of an existing wastewater treatment plant by designing and scheduling equipment maintenance related to the various wastewater treatment processes, which must be well established and scheduled to maintain the performance of the recommended treatment system by releasing treated wastewater of satisfactory quality and in compliance with current standards, thus ensuring the sustainability of the different sectors and notably reducing the treatment cost. When envisioning the future wastewater treatment plant as a key component of the circular economy, it becomes apparent that the continuously advancing treatment facility must be properly equipped and staffed with skilled personnel. This, combined with coordinated efforts of various kinds, will facilitate the production and valorization of treated water, helping to generate energy, raw materials, and high-quality recycled water. These resources can then support specific industrial sectors, water green areas and golf courses, or irrigate crops, marking the transition into the circular economy era.