High-precision dynamic model and life cycle assessment framework reduce decision-making risks for sludge-based carbon mitigation strategies

Sludge resource recovery is a promising strategy for mitigating carbon emissions from wastewater treatment plants (WWTPs). However, decision-making for carbon reduction strategies faces significant uncertainties, due to the coupling between wastewater and sludge treatment processes, as well as the inherent variability in sludge characteristics. To systematically quantify the carbon reduction potential of sludge resource recovery and mitigate decision-making risks, an integrated methodological framework was developed in this study by combining dynamic modeling and life cycle assessment (LCA), applied to a typical Anaerobic-Anoxic-Oxic process case. The dynamic model provided a calibrated, site-specific simulation of wastewater treatment processes, providing daily estimates of CH₄, N₂O, and fossil-derived CO₂ emissions, as well as sludge production and characteristics. The site-specific data generated by the model showed 89.11%–91.55% lower variability in sludge characteristics compared to generic literature data. These model-derived site-specific inputs reduced the uncertainty ranges in the LCA of sludge resource recovery, revealing that under current electricity conditions, emission offsets are limited to 41%–57% of the plant-wide carbon footprints. Under the assumed future cleaner electricity scenarios, sludge land use and anaerobic digestion coupled with land-use strategies were projected to approach or reach plant-wide net-zero emissions for the investigated WWTP, with net emissions as low as -2744 t CO2-eq by 2050.Furthermore, cleaner electricity mixes reduced the carbon reduction potential of sludge-to-energy conversion by 18% and 22% for anaerobic digestion with land use and pyrolysis alone, respectively. The integrated dynamic model-LCA framework substantially reduced decision-making risks for sludge-based carbon reduction by generating high-precision site-specific data. The study provides a scientific basis for optimizing plant-wide low-carbon strategy.