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Impact on the Sustainable Development Goals (SDGs)

Analysis of institutional authors

Castells, BlancaCorresponding AuthorParedes, RobertoAuthorLeón, DavidAuthorAmez, IsabelAuthor

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March 13, 2025
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Kinetic and thermodynamic insights into sewage sludge torrefaction: Energetic optimization and safety considerations

Publicated to: Energy Nexus. 17 100377- - 2025-03-01 17(), DOI: 10.1016/j.nexus.2025.100377

Authors:

Castells, Blanca; Paredes, Roberto; Leon, David; Amez, Isabel
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Affiliations

Univ Politecn Madrid, ETS Ingn Minas & Energia, Rios Rosas 21, Madrid 28003, Spain - Author
Univ Politecn Madrid, Lab Oficial JM Madariaga LOM, Madrid, Spain - Author
Univ Politecn Madrid, Tecnol Ctr TECMINERGY, Madrid, Spain - Author
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Abstract

In the current energetic scenario, biofuels play a crucial role, with torrefaction being one of the most popular pretreatments as it significantly reduces the main disadvantages of these fuels. This study provides novel insights into torrefied sewage sludge as a solid biofuel by examining both the energetic conversion process and associated safety issues. To do so, torrefaction was carried out at three different temperatures (220 degrees C, 250 degrees C, and 300 degrees C) and two residence times (30 and 60 min), resulting in seven distinct samples. These samples underwent proximate analysis, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) in air, nitrogen, and oxygen atmospheres to simulate combustion, pyrolysis, and determine heating values respectively. The analysis reveals that torrefaction at 300 degrees C for 60 min produces the best results, enhancing the higher heating value (HHV) by 6% and increasing reaction heat by 16%. Additionally, we observed lower pyrolysis activation energies in samples torrefied for 30 min compared to 60 min. The kinetic parameters were meticulously evaluated, showing a clear relationship between torrefaction parameters and pyrolysis activation energy. For instance, the activation energy (Ea) for raw sewage sludge was found to be between 338.02 kJ/mol and 375.43 kJ/mol. In contrast, torrefied samples showed reduced Ea values mostly under 300 kJ/mol. For the first time, we assessed self-ignition risk through TGA, finding that while most samples exhibit low risk, the increased heating value from torrefaction does elevate this risk. This comprehensive evaluation not only advances the understanding of sewage sludge torrefaction but also offers a practical framework for integrating biofuels into sustainable energy systems, supporting global efforts toward cleaner energy transitions.
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Keywords

BiomassBiomass pyrolysisClean water and sanitationCombustionDifferential scanning calorimetryFtirFueKinetic analysisModelPyrolysis characteristicsSelf-ignition risSelf-ignition riskSusceptibilityTgaThermal-analysisThermogravimetric analysisThermogravimetryTorrefaction

Quality index

Bibliometric impact. Analysis of the contribution and dissemination channel

The work has been published in the journal Energy Nexus due to its progression and the good impact it has achieved in recent years, according to the agency WoS (JCR), it has become a reference in its field. In the year of publication of the work, 2025, it was in position 26/376, thus managing to position itself as a Q1 (Primer Cuartil), in the category Environmental Sciences.

Independientemente del impacto esperado determinado por el canal de difusión, es importante destacar el impacto real observado de la propia aportación.

Según las diferentes agencias de indexación, el número de citas acumuladas por esta publicación hasta la fecha 2026-04-25:

  • WoS: 3
  • Scopus: 3
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Impact and social visibility

From the perspective of influence or social adoption, and based on metrics associated with mentions and interactions provided by agencies specializing in calculating the so-called "Alternative or Social Metrics," we can highlight as of 2026-04-25:

  • The use of this contribution in bookmarks, code forks, additions to favorite lists for recurrent reading, as well as general views, indicates that someone is using the publication as a basis for their current work. This may be a notable indicator of future more formal and academic citations. This claim is supported by the result of the "Capture" indicator, which yields a total of: 19 (PlumX).

It is essential to present evidence supporting full alignment with institutional principles and guidelines on Open Science and the Conservation and Dissemination of Intellectual Heritage. A clear example of this is:

  • The work has been submitted to a journal whose editorial policy allows open Open Access publication.
  • Assignment of a Handle/URN as an identifier within the deposit in the Institutional Repository: https://oa.upm.es/92406/

As a result of the publication of the work in the institutional repository, statistical usage data has been obtained that reflects its impact. In terms of dissemination, we can state that, as of

  • Views: 35
  • Downloads: 43
Continuing with the social impact of the work, it is important to emphasize that, due to its content, it can be assigned to the area of interest of ODS 6 - Clean water and sanitation, with a probability of 82% according to the mBERT algorithm developed by Aurora University.
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Leadership analysis of institutional authors

There is a significant leadership presence as some of the institution’s authors appear as the first or last signer, detailed as follows: First Author (CASTELLS SOMOZA, BLANCA) and Last Author (AMEZ ARENILLAS, ISABEL).

the author responsible for correspondence tasks has been CASTELLS SOMOZA, BLANCA.

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Project objectives

Los objetivos perseguidos en esta aportación se centran en profundizar en el proceso de torrefacción de lodos de depuradora como biocombustible sólido. Se pretende analizar el efecto de diferentes temperaturas (220 °C, 250 °C y 300 °C) y tiempos de residencia (30 y 60 minutos) sobre las propiedades energéticas y cinéticas del material. Asimismo, se busca evaluar mediante análisis termogravimétrico y calorimétrico las características de combustión, pirólisis y valores caloríficos. Otro objetivo es determinar los parámetros cinéticos, especialmente la energía de activación, y su relación con las condiciones de torrefacción. Finalmente, se pretende caracterizar el riesgo de autoignición asociado a los productos torrefactados para optimizar la seguridad en su uso energético.
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Most relevant results

Los resultados más relevantes del estudio se centran en la optimización energética y la seguridad de la torrefacción de lodos residuales. En primer lugar, la torrefacción a 300 °C durante 60 minutos incrementó el valor calorífico superior (HHV) en un 6% y aumentó el calor de reacción en un 16%. En segundo lugar, se observaron energías de activación para la pirólisis menores en muestras torrefactadas por 30 minutos en comparación con 60 minutos, con valores de Ea para lodos crudos entre 338,02 y 375,43 kJ/mol, y la mayoría de las muestras torrefactadas presentaron Ea inferiores a 300 kJ/mol. Finalmente, se evaluó por primera vez el riesgo de autoignición mediante análisis termogravimétrico, concluyendo que aunque la mayoría de las muestras presentan bajo riesgo, el aumento del valor calorífico eleva este riesgo.
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