Potential biomethane production from crop residues in China: Contributions to carbon neutrality

The Chinese government has set an ambitious goal of achieving carbon neutrality by 2060. Realizing negative greenhouse gas (GHG) emissions will require technologies like anaerobic digestion to recover biomethane from organic biomass. As the world's main grain-producing country, China has abundant crop residues, >85% of which were utilized as fertilizer, fodder, industrial material, biofuel, and base material in 2019. However, the potential contribution of crop residues to energy and reduced GHG emissions following anaerobic digestion have been scarcely evaluated. Based on crop yield and the field residue index, the annual quantity of crop residues in China from 2000 to 2019 was estimated. The annual crop residue yield increased between 2003 and 2014, and then remained constant at ~970 × 106 t/a, with an estimated 495 × 106 t/a being available for biomethane production. This corresponded to a potential biomethane yield of 82.25 × 109 m3/a, which could have met 29.2% of the annual natural gas consumption and 2.25% of the annual energy consumption in China in 2018 and 2019, respectively. Furthermore, the estimated potential GHG emission reduction was 197 × 106 t/a (CO2 equivalent), representing ~2% of China's GHG emissions in 2019. Nevertheless, to reach the expected goal, some crucial technical and equipment-oriented research and development should be promoted to adapt to the characteristics of China's crop residues and regional environment. Moreover, governmental support policies on subsidies would be required for the development of the biomethane industry, which should prioritize northern regions with relatively high quantities of crop residues.