Valorisation of Inorganic Fractions of Waste Generated by Hydrothermal Treatment of Sewage Sludge in Alkaline Cement

Ana Fernández-Jiménez (), Olga Maltseva, Angel Palomo, Narcisa Mihaela Marian, Michela Sturini, Maria Pia Riccardi, Michele Zema and Serena C. Tarantino
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Ana Fernández-Jiménez: Instituto Eduardo Torroja (IETcc), CSIC, 28001 Madrid, Spain
Olga Maltseva: Instituto Eduardo Torroja (IETcc), CSIC, 28001 Madrid, Spain
Angel Palomo: Instituto Eduardo Torroja (IETcc), CSIC, 28001 Madrid, Spain
Narcisa Mihaela Marian: Department of Chemistry, University of Pavia, 27100 Pavia, Italy
Michela Sturini: Department of Chemistry, University of Pavia, 27100 Pavia, Italy
Maria Pia Riccardi: Department of Earth and Environmental Sciences, University of Pavia, 27100 Pavia, Italy
Michele Zema: Department of Earth and Geoenvironmental Sciences, University of Bari, 70100 Bari, Italy
Serena C. Tarantino: Department of Chemistry, University of Pavia, 27100 Pavia, Italy

Sustainability, 2025, vol. 17, issue 12, 1-15

Abstract: Hydrothermal processing technology provides an innovative and promising solution to achieve significant reductions in the volume of sewage sludge and the recovery of raw materials. In this work, we evaluated the possibility of using inorganic mineral residue (IMR) from hydrothermal sewage treatment in a geopolymer binder. Initially, the waste was characterised, and thermal treatment was carried out at 800 °C to eliminate the organic matter. Calcined clay (3 h at 800 °C) was used to manufacture the geopolymer. Calcined clay/residue mixtures at ratios of 100/0, 90/10, and 80/20 were prepared and activated using a 6 M NaOH solution. The pastes were cured for 20 h at 85 °C, their compressive strengths were evaluated, and the reaction products were characterised using XRD and microscopy. The results show low reactivity in the residue. However, it was observed that some of the phosphorus present in the residue could be incorporated into the products of alkaline activation. A leaching study was also carried out, in which all the toxic metals remained confined except for chromium.

Keywords: geopolymer; sewage sludge; characterisation; leaching (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2025
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