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Converting waste paper sludge to sustainable aviation fuel (SAF) offers a circular economy strategy to decarbonize the aviation sector. This study develops a life-cycle assessment (LCA) for converting high-ash paper sludge to SAF in the U.S. using a catalytic sugar upgrading system that consists of ash removal, enzymatic hydrolysis, dehydration, aldol condensation, and hydroprocessing. The LCA is coupled with a process simulation for an industrial-scale biorefinery based on experimental data. We quantified the carbon intensity as 35.7–41.8 gCO2eq MJ–1 SAF (−636 to −584 gCO2eq per dry kg paper sludge) with acetone as a solvent, renewable fuel, and biobased chemicals; this is further reduced to 5.1–11.1 gCO2eq MJ–1 (−925 to −873 gCO2eq per dry kg paper sludge) if ash is recycled and used for substituting cement. Converting 1 dry kg paper sludge to SAF with acetone, renewable fuel, and biobased chemicals (−925 to −584 gCO2eq) is more climate beneficial than landfilling without landfill gas recovery (791 gCO2eq) and with landfill gas recovery (−294 gCO2eq). More than 330 million gallons of SAF can be produced annually (>4 million dry t paper sludge/year in the U.S.), resulting in a reduction of 2–7 million tCO2eq.
Lan et al. (2024) studied this question.