Environmental Assessment of Hydrothermal Treatment of Wet Bio-Residues from Forest-Based and Agro-Industries into Intermediate Bioenergy Carriers

Published February 5, 2024 | Version v1

Journal article Open

Hydrothermal carbonization (HTC) of low quality, wet biogenic residues into intermediate

bioenergy carriers can potentially contribute to a more flexible and stable renewable energy system

and reduce environmental impacts compared to current residue disposal practices. This study

quantifies the environmental impacts via life cycle assessment (LCA) of a novel hydrothermal

process for the treatment on an industrial scale of application of three wet biogenic residues (paper

bio-sludge, olive pomace, and orange peel) into bioenergy carriers, i.e., solid pellets and biogas.

A comprehensive attributional cradle-to-gate life cycle assessment (LCA) was conducted; the life

cycle impact assessment (LCIA) utilised the ReCiPe impact assessment method. A selection of

10 significant impact categories was prioritised. Reliability of this categorization was also ensured

through a sensitivity analysis carried out using Monte Carlo simulation. Climate change, particulate

matter formation and terrestrial acidification impact categories showed the highest reliability, while

for freshwater ecotoxicity and freshwater eutrophication impact categories in the study suggest the

need for more robust data and further investigation. The climate change impact category presents

the following values, as kg CO2eq/t residue: pulp and paper bio-sludge (PPB), 17.9; olive pomace (OP),

−1290; orange peel (ORP),−1301. The LCA study compared electricity yields of the hydrothermal

treatment process with conventional treatment processes for each of the target residue streams. The

environmental performance of the proposed hydrothermal treatment benefits significantly from

the combination of intermediate bioenergy carriers (pellets) from the solid fraction with biogas

production from the liquid fraction. Avoided emissions due to the heat recovery provide further

environmental benefits. The LCIA results show that the carbon footprint of the F-CUBED production

system, as kgCO2eq/kWhe, accounts for –4.56,−0.63, and−0.25 for paper bio-sludge, olive pomace

and orange peel, respectively.

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