What question did this study set out to answer?

The research aims to assess the environmental benefits of integrating anaerobic digestion with pyrolysis and hydrothermal carbonization for processing cattle slurry and grass silage.

January 22, 2026Open Access

Consequential Life Cycle Assessment of Integrated Anaerobic Digestion–Pyrolysis–HTC Systems for Bioenergy and Biofertiliser from Cattle Slurry and Grass Silage

Puntos clave

The research aims to assess the environmental benefits of integrating anaerobic digestion with pyrolysis and hydrothermal carbonization for processing cattle slurry and grass silage.
Conducted a consequential life cycle assessment for six scenarios based on 1 ton of feedstock.
Compared two standalone anaerobic digestion systems with four integrated anaerobic digestion–pyrolysis/hydrothermal carbonization systems.
Evaluated environmental impacts across multiple categories including climate change and resource depletion.
Integrated systems outperformed standalone anaerobic digestion systems across all impact categories.
Climate change impacts reduced by up to 84%, freshwater eutrophication by 86%, and fossil fuel depletion by 99% compared to a fossil-based reference.
The AD–HTC bioelectricity scenario achieved the best performance, with higher hydrochar yields and lower energy demands.

Resumen

This study evaluates the environmental outcomes of integrating anaerobic digestion (AD) with pyrolysis (Py) and hydrothermal carbonization (HTC) to treat cattle slurry and grass silage in an Irish agricultural context. A consequential life cycle assessment (CLCA) was carried out for six scenarios based on 1 t of feedstock (0.4:0.6 cattle slurry/grass silage on a VS basis): two standalone AD systems (producing bioelectricity and biomethane) and four integrated AD–Py/HTC systems with different product utilisation pathways. Across all impact categories, the integrated systems performed better than standalone AD. This improvement is mainly due to the surplus bioenergy (electricity, biomethane, hydrocarbon fuel, hydrochar) that replaces marginal fossil energy (hard coal, natural gas and heavy fuel oil), together with the displacement of mineral NPK fertilisers by digestate-derived biochar and HTC process water. Among the configurations, the AD–HTC bioelectricity scenario (S4) achieved the best overall performance, driven by higher hydrochar yields, a favourable heating value, and a lower pretreatment energy demand compared with Py-based options. Across the integrated scenarios, climate change, freshwater eutrophication, and fossil depletion impacts were reduced by up to 84%, 86%, and 99%, respectively, relative to the fossil-based reference system, while avoiding digestate and fertiliser application reduced terrestrial acidification by up to 74%. Overall, the results show that the cascading utilisation of digestate via AD–Py/HTC can simultaneously enhance bioenergy production and nutrient recycling, providing a robust pathway for low-emission management of agricultural residues. These findings are directly relevant to Ireland’s renewable energy and circular economy targets and are transferable to other livestock-intensive regions seeking to valorise slurry and grass-based residues as low-carbon energy and biofertiliser resources.

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