The urban wastewater treatment plants can be an important part of circular sustainability due to integration of energy production and resource recovery during clean water production. Currently the main drivers for developing wastewater industry are global nutrient needs and water and energy recovery from wastewater. The article presents current trends in wastewater treatment plants development based on Circular Economy assumptions, challenges and barriers which prevent the implementation of the CE and Smart Cities concept with WWTPs as an important player. WWTPs in the near future are to become “ecologically sustainable” technological systems and a very important nexus in SMART cities.