Sustainable management of antibiotic-contaminated livestock carcasses for climate change mitigation.

Using antibiotics in livestock farming has raised serious concerns, particularly about greenhouse gas (GHG) emissions and the discharge of residual antibiotics from livestock carcasses (LSC). Due to the low C-to-N ratio (≤4.4) and persistent antibiotic residues post-rendering, dead livestock are not suitable for conventional treatments such as composting and anaerobic digestion. This study presents a thermochemical conversion strategy using carbon dioxide (CO2) as a mild oxidant. CO2 facilitated gas-phase reactions with pyrolytic volatile matter, shifting carbon distribution toward valuable syngas production and minimising unwanted condensable products. Multi-stage pyrolysis yielded only modest gains due to reaction rate limitation, catalytic pyrolysis with a Ni-based catalyst increased syngas production to 25.91 mmol g-1 under CO2 (an increase of 28 % over N2 conditions). CO2 contributes to the degradation of polycyclic aromatic hydrocarbons (PAHs) and residual antibiotics, improving the environmental safety of the pyrolysis process. The CO2-assisted pyrolysis had a lower carbon footprint (-0.42 g CO2-eq g-1), compared to landfilling, which had higher emissions (16.48 g CO2-eq g-1). These findings reveal a carbon-negative, resource-efficient method for safely and sustainably treating antibiotic-contaminated carcass waste.