Potential of biochar production and carbon emission mitigation through co-pyrolysis of cotton straw and mulch film waste in Xinjiang, China

As China's largest crop and cotton production region, Xinjiang faces significant challenges in managing and reusing agricultural residues such as crop straw, cotton straw, and mulch film waste in the agricultural sector. To promote the efficient utilization of these residues and guide sustainable agricultural waste management practices in Xinjiang, this study calculated the collectible quantities of major crop straw (maize, wheat, and cotton) using grass-to-grain ratios and straw collectible coefficients, and determined the quantity of recyclable mulch film based on application and recovery rates. Furthermore, it assessed the biochar production potential and carbon reduction benefits through life cycle assessment (LCA). The pyrolysis of straw (maize, wheat, and cotton) and mulch film for biochar production yielded a net CO2e reduction of 2.05 × 107 and 2.67 × 105 t, respectively. Considering that wheat straw is primarily returned to fields and maize straw serves mainly as animal feed, the biochar production potential of cotton straw alone was estimated at 3.48 × 106 t, corresponding to a net CO2e reduction of 1.01 × 107 t. Although the pyrolysis of mulch film alone produces minimal biochar, co-pyrolysis of all recyclable mulch film with cotton straw at a ratio of 1:4 significantly improves biochar yield, generating 2.24 × 105 t of biochar and achieving a net CO2e emission reduction of 3.43 × 106 t. These results demonstrate that co-pyrolysis significantly enhances both biochar production and carbon emission reduction compared with the pyrolysis of mulch film alone. Overall, this study not only provides a scientific basis for the efficient utilization of major crop residues in Xinjiang but also offers practical insights for the integrated management of cotton straw and mulch film waste in cotton-producing regions.