Room: Poster Area
Date: Thursday, 21 May 2026
Time: 11:30 - 12:45 CEST
Session code 5CV.3
Hydrothermal processing
The Fate of Fatty Acids during Hydrothermal Carbonization under Ultra-High-Pressure Conditions
Short Introductive summary
Sewage sludge is often viewed as a disposal problem, yet it represents a largely untapped resource rich in organic matter and lipids. This work demonstrates how hydrothermal carbonization (HTC), when operated under ultra-high-pressure conditions, can fundamentally change the value proposition of sludge treatment. By applying HTC at 200–240 °C and pressures up to 250 bar, we show that the process strongly upgrades the liquid phase, yielding exceptionally high concentrations of both volatile fatty acids (VFAs) and long-chain fatty acids. Formic acid dominates the VFA spectrum (430–440 mg/ g sludge), while acetic acid increases sharply with temperature, reaching nearly 190 mg/ g at 240 °C. In parallel, the liquid phase contains unusually high levels of C16–C24 fatty acid methyl esters, with methyl linoleate concentrations up to 3000 mg/ L, values comparable to hydrothermal liquefaction. These findings reposition HTC from a solid-focused treatment into a versatile, multi-product conversion route, capable of generating energy-dense and chemically rich liquid streams alongside hydrochar, supporting circular bioeconomy strategies for wastewater treatment.
Presenter
Stergios VAKALIS
National Technical University of Athens, School of Chemical Engineering, Process Analysis and Plant Design, GREECE
Presenter's biography
Stergios Vakalis is an Assistant Professor of Energy Processes at the School of Chemical Engineering, NTUA. Stergios works primarily on energy analysis, thermochemical production of biofuels and modeling of energy processes.
Biographies and Short introductive summaries are supplied directly by presenters and are published here unedited
Co-authors:
S. Vakalis, National Technical University of Athens, GREECE
Session reference: 5CV.3.25