What question did this study set out to answer?

This study aims to analyze the emission of volatile organic compounds during hydrothermal carbonization of different biomass materials.

May 14, 2026Open Access

Insights into the mechanisms of volatile organic compounds formation during the hydrothermal carbonization of olive tree sawdust, rice husk and wine pomace

Key Points

This study aims to analyze the emission of volatile organic compounds during hydrothermal carbonization of different biomass materials.
Hydrochars produced from olive tree sawdust, rice husk, and wine pomace at 180 and 220 °C for 2 and 6 hours.
VOC emissions quantified in a microchamber at temperatures of 23, 40, and 80 °C.
Samples analyzed using thermal desorption gas chromatography and mass spectrometry with mass-specific emission factors reported.
Olive tree sawdust hydrochars emitted the highest VOC concentrations at 86.1 µg⋅g−1⋅h−1, followed by rice husk at 33.5 µg⋅g−1⋅h−1, and wine pomace at 9.2 µg⋅g−1⋅h−1.
Peak emissions were recorded at 220 °C for 6 hours from olive tree sawdust with 152.7 µg⋅g−1⋅h−1.
Oxygenated compounds dominated emissions, with feedstock type being the main factor in reducing VOC emissions.

Abstract

• The µ-CTE enabled emerged screening of VOC emissions from hydrochars. • VOC emissions determined by feedstock type; olive tree hydrochars emitted most. • Main VOC were oxygenates, lipids, benzenoids, heterocycles, and hydrocarbons. • RH hydrochars emitted furans while OS lipid and phenolic compounds. • VOC profiling highlights how production choices shape downstream odour risk. Hydrothermal carbonization is increasingly used to convert wet biomass residues into carbon-rich hydrochar, yet fresh hydrochar can exhibit strong odours that indicate retained volatile organic compounds. In this study, hydrochars were produced from wine pomace, olive tree sawdust, and rice husk at two hydrothermal carbonization temperatures (180 and 220 °C) and two residence times (2 and 6 h). The VOCs emissions were quantified in a microchamber at 23, 40 and 80 °C, collected on Tenax under a controlled nitrogen flow, and analysed by thermal desorption gas chromatography and mass spectrometry. Results are reported as mass-specific emission factors (micrograms per gram per hour) using toluene-equivalent semi-quantification and class-resolved interpretation. Across all conditions, olive tree sawdust hydrochars emitted the highest concentrations of VOCs, followed by rice husk and wine pomace hydrochars, with grand mean values of 86.1, 33.5, and 9.2 µg⋅g −1 ⋅h −1 , respectively. Peak emissions were observed for olive tree sawdust hydrochar produced at 220 °C for 6 h and extracted at 80 °C (152.7 µg⋅g −1 ⋅h −1 ); corresponding maxima for rice husk and wine pomace were substantially lower. Increasing microchamber temperature consistently mobilized semi-volatile compounds and shifted profiles towards less volatile fractions, supporting temperature stepping as a rapid diagnostic for batch comparison. Oxygenated compounds dominated overall. Rice husk hydrochars showed a stronger carbohydrate-derived furanic signature, whereas olive tree sawdust hydrochars additionally released abundant lipid- and phenolic-related compounds. Feedstock selection emerged as the primary lever to reduce emissions, while process severity and handling temperature further shaped both magnitude and composition.

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