Comparative Analysis of Greenhouse Gas Emission Factors for Recyclables from Municipal Solid Waste
Recyclables constitute a significant fraction of municipal solid waste (MSW) and hold substantial potential for resource utilization and greenhouse gas (GHG) emission reduction, contributing to carbon peak and carbon neutrality goals. However, reported GHG emission factors (EFs) for various recyclables vary widely across databases and literature, ranging from -19,110 to -125 kgCO2-eq·t⁻¹, with significant differences both among categories and within the same category, complicating accurate accounting. This study systematically integrates literature data on EFs for different recyclable categories, focusing on identifying factors causing intra-category variability. Data were collected from global databases (ecoinvent, WARM, CPCD, NAEI) and peer-reviewed studies over the past two decades, normalized to a functional unit of 1 tonne of recyclable. Statistical analysis (mean ± standard deviation) provided reference ranges for each category. Results show paper recyclables EFs range from -3,140 to 270 kgCO2-eq·t⁻¹, with corrugated cardboard and writing paper exhibiting higher absolute values than packaging paper due to structural strength and resource value. Plastic recyclables EFs range from -3,096 to -566 kgCO2-eq·t⁻¹, with EPS showing the highest reduction potential, followed by PET and PVC, then HDPE, LDPE, PP, and other plastics. Key influencing factors include functional unit definition, accounting scenario, system boundary, electricity emission factor selection, and calculation assumptions. The study recommends selecting EFs matching the specific accounting scenario and performing error analysis. Data gaps remain for LDPE, EPS, and other plastics, necessitating further experimental or field data. To enhance accuracy, calibration methods such as process-level and life-cycle inventory data calibration are proposed. This work provides a scientific basis for EF selection and calibration in GHG accounting of recyclables.