This work explores the potential of hydrothermal carbonization (HTC) for converting wet biowaste into energy-rich solid fuels. Various organic residues—including spent coffee grounds, olive pomace, grape marc, hemp, and digestate—were treated at 220 °C for 1 hour. The aim was to assess the impact of HTC on fuel properties through elemental and proximate analysis, and higher heating value (HHV). Results showed a consistent increase in carbon content and a reduction in H/C and O/C ratios, indicating effective dehydrogenation and decarboxylation. These changes led to higher fixed carbon content and improved HHVs, up to 30.41 MJ/kg for olive pomace-derived hydrochar. The Van Krevelen diagram confirmed the transformation of hydrochars toward coal-like materials, especially lignite and peat regions. Spent coffee grounds and olive pomace produced hydrochars with the best energy profiles and solid yields above 50%, while digestate showed limited carbonization and low HHV. Overall, HTC demonstrated high effectiveness in upgrading biowaste into solid fuels, supporting its role in biowaste valorization within circular bioeconomy frameworks.
From Agroindustrial Residues to Hydrochar: Characterization and Energy Properties
Gianluigi Farru
;Mona Ghaslani;Giovanna Cappai
2025-01-01
Abstract
This work explores the potential of hydrothermal carbonization (HTC) for converting wet biowaste into energy-rich solid fuels. Various organic residues—including spent coffee grounds, olive pomace, grape marc, hemp, and digestate—were treated at 220 °C for 1 hour. The aim was to assess the impact of HTC on fuel properties through elemental and proximate analysis, and higher heating value (HHV). Results showed a consistent increase in carbon content and a reduction in H/C and O/C ratios, indicating effective dehydrogenation and decarboxylation. These changes led to higher fixed carbon content and improved HHVs, up to 30.41 MJ/kg for olive pomace-derived hydrochar. The Van Krevelen diagram confirmed the transformation of hydrochars toward coal-like materials, especially lignite and peat regions. Spent coffee grounds and olive pomace produced hydrochars with the best energy profiles and solid yields above 50%, while digestate showed limited carbonization and low HHV. Overall, HTC demonstrated high effectiveness in upgrading biowaste into solid fuels, supporting its role in biowaste valorization within circular bioeconomy frameworks.
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