A comparative environmental life cycle assessment of rice straw-based bioenergy projects in China

Bioenergy is a promising solution for greenhouse gas (GHG) emissions mitigation. However, the emissions resulting from the different production stages must be quantified and evaluated. The life cycle assessment (LCA) method was used to compare and quantify the environmental burdens of three rice straw (RS) utilization scenarios for producing biogas, briquette fuel, and syngas. To our knowledge, this is the first study that applies the LCA approach to assess these three bioenergy scenarios in a single study where the main goal was to determine the most sustainable option. A total of 10 mid-point impact categories were investigated. The results indicated that the three scenarios achieved net positive energy and net negative GHG balances. The briquette fuel scenarios had the highest net energy balance (11,115 MJ/tonne dry RS), while the syngas scenario had the highest net GHG (-2,315 kg CO₂-eq./tonne dry RS). Moreover, the syngas scenario was the most beneficial to the environment, achieving negative results in 9 out of the 10 impact categories; the largest was marine ecotoxicity (-853,897 kg 1,4-DB-eq./tonne dry RS). The biogas scenario achieved emission savings in 3 out of the 10 categories. Although the briquette fuel scenario had no negative values in the 10 categories, its overall contribution to environmental burdens was relatively low. Overall, the order of the three scenarios in terms of the most sustainable option is syngas > briquette fuel > biogas.