Nowadays, the main challenge for industrial and municipal enterprises is related to the tightening regulations and recommendations regarding environmental protection, which have been included in the circular economy (CE) package. Enterprises from all sectors, including water and sewage management, are obliged to actively participate in the CE transition. Modern wastewater treatment plants (WWTPs) should include actions aimed at a more sustainable use of available resources (water, energy, raw materials) to contribute to the protection of natural resources. In this way, they can be treated as resource facilities. This paper proposes a conceptual framework for a ‘Wastewater Treatment Plant of the Future’ that includes several technological solutions that take into account circular management of waste streams generated in WWTPs, such as wastewater (WW), sewage sludge (SS) and sewage sludge ash (SSA). Many actions have been already taken to modernize and build WWTPs that can respond to current and future challenges related to environmental protection. In the case of a CE ‘Wastewater Treatment Plant of the Future’, the recovery of water, energy and raw materials from available waste streams is strongly recommended. The implementation of CE solutions in analyzed facilities is incorporated into many strategies and policy frameworks, such as national and international (including European) documents. The proposed CE solutions could indirectly contribute to satisfying significant technological, social and environmental needs of the current and future generations, which is in line with sustainability principles.