Carbon Circularity

Review

Hydrothermal Carbonization of Sewage Sludge: A Pathway toward Sustainable Energy Transition and Regional Development

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https://doi.org/10.54963/cc.v1i1.2046
Bail, A., Soares, T. M. M., & Flórez, A. A. G. (2025). Hydrothermal Carbonization of Sewage Sludge: A Pathway toward Sustainable Energy Transition and Regional Development. Carbon Circularity, 1(1), 43–59. https://doi.org/10.54963/cc.v1i1.2046
Volume 1 Issue 1 (2025): In Progress

Authors

  • Alesandro Bail

    Group of Materials Chemistry and Sustainable Technologies, Federal Technological University of Paraná (UTFPR), Londrina 86036-700, Brazil
  • Tatiana Micaela Miguel Soares

    Group of Materials Chemistry and Sustainable Technologies, Federal Technological University of Paraná (UTFPR), Londrina 86036-700, Brazil
  • Arley Andrés Gutiérrez Flórez

    Group of Materials Chemistry and Sustainable Technologies, Federal Technological University of Paraná (UTFPR), Londrina 86036-700, Brazi

Received: 9 November 2025 | Revised: 4 December 2025 | Accepted: 15 December 2025 | Published Online: 22 December 2025

The transition toward low-carbon energy systems requires technologies capable of converting residual biomass into value-added energy carriers. In this context, hydrothermal carbonization (HTC) of sewage sludge (SS) has emerged as a promising pathway for producing solid biofuels while addressing persistent challenges in waste management and sanitation. This study evaluates the technological basis, environmental implications, and regional development potential of SS-HTC within renewable energy and decarbonization strategies. HTC enables the direct processing of wet sewage sludge, avoiding energy-intensive drying steps and generating a carbon-rich hydrochar with reduced moisture content and improved fuel properties compared to the raw material. In addition to the solid fraction, the process produces a nutrient-rich liquid stream that can be further valorized, supporting circular resource management and integrated waste-to-energy systems. Although the estimated global production potential of SS-derived hydrochar (approximately 45 million dry tons) is insufficient to replace fossil coal on a large scale, its targeted use in selected industrial sectors can partially substitute mineral coal, contributing to greenhouse gas mitigation and incremental decarbonization. Beyond its technological advantages, SS-HTC offers opportunities for regional development, particularly in areas with expanding wastewater treatment infrastructure. Integrating HTC into sanitation systems enables localized biofuel production, reduces dependence on imported coal, and supports industrial diversification. The State of Paraná, Brazil, with a population of 11.5 million and sanitation coverage of approximately 81%, exemplifies a favorable context in which SS-HTC can enhance regional competitiveness while advancing environmental sustainability and socio-economic development within the broader low-carbon transition.

Keywords:

Circular Economy Waste-to-Energy Systems Energy Transition

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