Global Warming Potential of Electricity from Sodium Hydroxide Pretreated Napier Grass Biogas: a Cradle-to-Gate Life Cycle Assessment

Napier grass was investigated as a bio-energy feedstock for Thailand. Laboratory anaerobic digestion and cradle-to-gate life cycle assessment (LCA) determined electricity generation’s global warming potential (GWP). Untreated and 1 % w/v NaOH pretreated biomass were digested. Pretreatment significantly increased cumulative biogas yield by up to 49 %, with 538.9 ± 22.3 mg/gVS at the highest F/I ratio. The LCA, based on primary experimental data and adjusted secondary data for the 2019 Thai electricity mix, characterized GWP per 1 kWh. Untreated systems exhibited GWP between 2.86–3.82 kg CO2e/kWh. However, pretreatment raised emissions to 7.01–8.26 kg CO2e/kWh; this was primarily due to the high emissions from NaOH manufacture and neutralization. Substituting 40 % of synthetic nitrogen fertilizer with cattle manure nearly halved both footprints, and a fully organic regime resulted in the untreated system’s GWP being reduced to 0.57 kg CO2e/kWh, which falls below the 2019 Thai grid factor of 0.599 kg CO2e/kWh. These findings indicate that while reactor performance is improved by NaOH pretreatment, climate benefits are offered only when aggressive fertilizer optimization.