Wastewater treatment plants (WWTPs) provide solutions to the treatment challenges of wastewater every day. Nevertheless, traditional wastewater treatment only focuses on removing pollutants from wastewater which often results in losing valuable materials like nutrients and metals. However, increase in population, resource demands, and waste production have influenced the current infrastructure design. Recently, WWTPs are being recognized as water resource recovery facilities that reclaim clean water and other resources while meeting water quality standards. Limitations in resource availability drive a transition from managing waste products like wastewater toward the recovery of valuable resources from them. Furthermore, wastewater valorization is garnering considerable interest in reducing environmental concerns, supporting sustainability, and progressing in the circular bioeconomy. On this basis, resource recovery methods encompass a variety of processes, including biochemical and physicochemical approaches along with innovative bio-based methods. Among them, biological techniques offer effective approaches to transform wastewater resources into renewable energy. Given the rising global energy demand and the threat it poses to non-renewable fuels, the Paris Climate Agreement (2015) also highlighted the significance of energy recovery from WWTPs. In this sense, various waste-to-energy systems, such as biogas energy production, thermal arc plasma gasification, anaerobic digestion processes, microbial fuel cell technology, and lipidic biomass conversion into biodiesel, have been investigated to reclaim energy. Overall, the use of wastewater can greatly improve the economic viability of renewable fuel production, contributing to sustainable development. Considering this, the present chapter emphasizes the potential of wastewater valorization to produce renewable energy.