Life cycle energy consumption and GHG emissions analysis of a cellulosic ethanol biorefinery: a scenario-based study on process waste valorization strategies.

As an advanced biofuel, cellulosic ethanol holds strong potential for mitigating greenhouse gas (GHG) emissions while promoting the valorization of agricultural residues, making it a key contributor to low-carbon energy transitions. This study conducts a comprehensive life cycle assessment (LCA) based on real operational data from a commercial-scale ethanol plant in Heilongjiang Province, China, to evaluate the environmental performance of ethanol production under six scenarios. These range from a baseline fully reliant on fossil fuels to progressively integrated systems utilizing lignin for electricity, biomass for steam, and biogas from anaerobic digestion of waste stillage. The most optimized configuration (Scenario 5) achieves a 95.9 % reduction in life cycle GHG emissions-from 2831.73 kg CO2 eq./t ethanol in the baseline to 117.11 kg CO2 eq./t ethanol-alongside a 62 % reduction in primary energy consumption, from 24,789 MJ to 9313.6 MJ per ton of ethanol. These improvements are primarily attributed to the combined recovery of electricity from lignin, slurry, and biogas, as well as the use of biomass-derived steam. Sensitivity analysis reveals that steam and electricity consumption are the dominant contributors to GHG emissions in fossil-based systems, while chemical inputs-such as sulfuric acid and ammonia-become increasingly influential in optimized scenarios. The findings underscore the critical role of integrated waste-to-energy pathways in enhancing both energy efficiency and climate performance. Policy recommendations focus on promoting waste-to-energy integration, such as increasing biomass-derived steam use and expanding anaerobic digestion and co-firing systems.