Carbon footprint reduction and process simulation of a combined biomass anaerobic digestion-gasification system

The anaerobic digestion-gasification coupled technology, as an innovative pathway for efficient biomass conversion, significantly enhances biomass treatment and conversion efficiency. This technology demonstrates broad application prospects in the context of achieving the “dual carbon” goals. In this study, machine learning methods were employed to integrate traditional anaerobic digestion models with gasification process models. A dynamic simulation system for the coupled anaerobic digestion-gasification process of biomass was constructed. The dynamic evolution patterns of key products throughout the entire process from anaerobic digestion to gasification were systematically revealed. Simulation and experimental validation results indicated that the coupled model achieved an average prediction accuracy of 91.3% for the concentrations of major gas products (including H₂, CO, CH₄, CO₂) during the gasification stage. Compared with traditional single gasification models, the prediction accuracy was improved by 12.5%, demonstrating excellent generalization and prediction capabilities. In the initial stage of anaerobic digestion (0−6 days), the system exhibited high methanogenic activity. Volatile fatty acids were rapidly degraded, and the cumulative methane production increased rapidly to 136.4 mL/g, marking the main methanogenic phase of the digestion system. As anaerobic digestion progressed, significant changes were observed in the physicochemical properties of the digestate. The contents of C and O elements showed an overall decreasing trend: C decreased from 34.14% to 29.11%, and O decreased from 30.05% to 20.10%. These results reflected the decomposition of organic components and their conversion into CO₂ and CH₄. The N element content increased from 2.15% to 2.57%, primarily due to the relative nitrogen enrichment resulting from the degradation of carbon-containing components. In terms of carbon emission reduction benefits, the CO₂ emission equivalent per unit of biomass input initially increased and then decreased with digestion time. The CO₂ emission equivalent of the coupled system reached its highest value (0.0694 gCO₂eq) on the third day of anaerobic digestion, indicating the optimal carbon reduction performance of the system at this time point. This study provides critical theoretical support for the engineering application of biomass cascade utilization technology.