Abstract Wastewater treatment plants (WWTPs) are traditionally known as energy-intensive facilities, where substantial energy consumption not only results in higher operational costs but also contributes to significant indirect carbon emissions. These emissions, primarily stemming from energy use, contradict the global agenda of achieving carbon neutrality. This review investigates strategies for transforming WWTPs into energy self-sufficient systems. First, the main sources of energy consumption within WWTPs are identified, along with key influencing factors such as treatment technologies, plant scale, and operational strategies. Based on this foundation, three main pathways toward energy neutrality are systematically examined: (1) energy conservation, (2) energy recovery, and (3) utilization of external renewable energy sources. A comprehensive analysis of emerging energy-saving technologies in wastewater treatment processes is presented, followed by a detailed discussion on the recovery potential of embedded energy in wastewater, including organic energy, thermal energy, and hydraulic energy. Recent advances in energy regeneration technologies and their feasibility of application in WWTPs are also reviewed. Additionally, several case studies of WWTPs that have successfully implemented these strategies are examined to demonstrate the practical effectiveness of transitioning toward energy neutrality. Finally, a roadmap is proposed to achieve energy self-sufficiency in WWTPs, emphasizing a core strategy of “carbon redirection + anaerobic digestion of sludge” for energy recovery, complemented by energy conservation measures and renewable energy utilization. The technical route is supported by practical calculations of potential energy savings. Despite promising progress, further empirical studies are necessary to verify these strategies under varying conditions and to explore optimized approaches for future energy-neutral wastewater management.
Song et al. (2025) studied this question.