Biochar Production from Rice Husk: A Comparative Life Cycle Assessment of Grid, Biomass, and Solar-Powered Pyrolysis

Rice husk, which accounts for approximately 22% of global rice production, is often disposed of by open field burning, causing significant greenhouse gas (GHG) emissions and air pollution. Converting rice husk into biochar via pyrolysis offers a sustainable waste management and climate mitigation pathway; however, the environmental performance of biochar production is highly sensitive to the energy source used. Hence, this study presents a gate-to-gate life cycle assessment of biochar production from rice husk via slow pyrolysis at 500 °C under three energy supply scenarios: grid electricity, biomass combustion, and photovoltaic solar energy. Using the ReCiPe 2016 methodology, environmental impacts were evaluated across four categories such as Global Warming Potential (GWP), Human Toxicity Potential (HTP), Acidification Potential (AP), and Abiotic Depletion Potential (ADP), with all process parameters held constant except the energy source. The results demonstrate that energy supply is the dominant determinant of environmental performance and the photovoltaic solar-assisted biochar production route showed superior performance across all categories, with gross production impacts for 1 ton biochar of 24.0 kg CO2-eq (GWP), 5.6 kg 1,4-DCB-eq (HTP), 0.09 kg SO2-eq (AP), and 259.9 MJ (ADP), representing 48-165-fold improvements over grid electricity. When accounting for carbon sequestration (2800 kg CO2-eq per ton biochar), all scenarios achieved net negative GWP, ranging from −2776.0 kg CO2-eq (solar PV) to −1562.5 kg CO2-eq (grid electricity), representing 78% variation attributable to energy source. Contribution analysis revealed pyrolysis heating accounts for 95.6% of environmental impacts, with no trade-offs among impact categories. The findings recommend photovoltaic solar energy for new biochar facilities, biomass combustion for co-located agricultural operations, and avoidance of grid electricity unless grids achieve substantial decarbonization.