Integration of Sludge-to-Energy

Wastewater sludge generation is increasing quickly around the world due to urban growth, rising populations, and expanding municipal wastewater treatment facilities. Traditional methods of sludge disposal, such as landfilling, illegal dumping, and incineration, are no longer sustainable because of rising environmental impacts, greenhouse gas emissions, energy costs, and limited land availability. In the last decade, sludge-to-energy technologies have emerged as a viable way to turn sludge from waste into a valuable renewable energy source. This review paper compiles a large number of scientific studies from 2015 to 2024, focusing on anaerobic digestion, pyrolysis, gasification, hydrothermal processes, co-digestion strategies, biochar production, IoT-enabled smart monitoring, and integrated circular economy models. With insights from over 60 research contributions—including works by Oladejo et al., Appels et al., Batstone & Jensen, Kang et al., Basu & Butler, Trabelsi et al., Marin et al., Dai et al., and many others—this 80-page review offers a thorough overview of the development, performance improvements, digital innovations, environmental effects, and policy factors that are influencing sludge-based bioenergy systems.