Renewable energy integration in wastewater treatment plants: A review of pathways to energy self-sufficiency and sustainability

One of the industries with a huge role in public health and environmental protection is municipal wastewater treatment plants (WWTPs). However, they face serious challenges, such as high energy consumption, operational expenses, and greenhouse gas emissions. This review analyzes energy demand across all WWTP stages, highlighting energy-intensive processes such as aeration, membrane filtration, and sludge drying. While previous studies often examine renewable energy technologies in isolation, this work uniquely integrates solar energy, wind power, geothermal, and biogas within a unified WWTP framework, emphasizing techno-economic feasibility, operational reliability, and carbon mitigation. The study focuses on integrating these renewable sources, with a particular focus on biogas from anaerobic digestion (AD) as an on-site energy carrier. Solar and geothermal energy are explored for combined thermal and electrical applications, subject to site-specific limitations. Finally, this review moves the field forward by critically looking at new multigeneration ideas that can provide electricity, thermal energy, fresh water, hydrogen, and bioproducts all at once. This perspective identifies gaps in the coordinated application of renewable energy and multigeneration strategies, offering a roadmap for transforming WWTPs into sustainable resource recovery hubs. Future work is proposed on digital twin modeling, AI-driven operational optimization, and advanced geothermal and solar technologies to further enhance energy efficiency and system resilience.