Energy Valorization and Resource Recovery from Municipal Sewage Sludge: Evolution, Recent Advances, and Future Prospects

Pietro Romano (), Adriana Zuffranieri and Gabriele Di Giacomo ()
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Pietro Romano: Department of Industrial and Information Engineering and of Economics (DIIIE), Engineering Headquarters of Roio, University of L’Aquila, 67100 L’Aquila, Italy
Adriana Zuffranieri: Department of Industrial and Information Engineering and of Economics (DIIIE), Engineering Headquarters of Roio, University of L’Aquila, 67100 L’Aquila, Italy
Gabriele Di Giacomo: Independent Researcher, 64025 Pineto, Italy

Energies, 2025, vol. 18, issue 13, 1-32

Abstract: Municipal sewage sludge, a by-product of urban wastewater treatment, is increasingly recognized to be a strategic resource rather than a disposal burden. Traditional management practices, such as landfilling, incineration, and land application, are facing growing limitations due to environmental risks, regulatory pressures, and the underuse of the sludge’s energy and nutrient potential. This review examines the evolution of sludge management, focusing on technologies that enable energy recovery and resource valorization. The transition from linear treatment systems toward integrated biorefineries is underway, combining biological, thermal, and chemical processes. Anaerobic digestion remains the most widely used energy-positive method, but it is significantly improved by processes such as thermal hydrolysis, hydrothermal carbonization, and wet oxidation. Among these, hydrothermal carbonization stands out for its scalability, energy efficiency, and phosphorus-rich hydrochar production, although implementation barriers remain. Economic feasibility is highly context-dependent, being shaped by capital costs, energy prices, product markets, and policy incentives. This review identifies key gaps, including the need for standardized treatment models, decentralized processing hubs, and safe residual management. Supportive regulation and economic instruments will be essential to facilitate widespread adoption. In conclusion, sustainable sludge management depends on modular, integrated systems that recover energy and nutrients while meeting environmental standards. A coordinated approach across technology, policy, and economics is vital to unlock the full value of this critical waste stream.

Keywords: sewage sludge; municipal wastewater; waste-to-energy; biorefinery; hydro-thermal carbonization; hydrochar (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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