Greenhouse Gas Emissions from Co-Composting of Green Waste and Kitchen Waste at Different Ratios

With the rapid expansion of urban green spaces and the increasing amount of domestic waste, efficient and sustainable treatment of green waste (GW) and kitchen waste (KW) has become a pressing issue. Co-composting offers a green and low-carbon solution, yet a systematic understanding of its greenhouse gas (GHG) emission dynamics remains lacking. This study aims to investigate the impact of varying GW:KW ratios on GHG emissions during composting, in order to identify optimal mixing strategies and sup-port the development of low-carbon urban waste management systems. Six treatments with different GW:KW ratios (10:0, 9:1, 8:2, 7:3, 6:4, and 5:5) were evaluated under continuous aeration for 42 days. Results showed: (1) All treatments exhibited a typical composting temperature profile (mesophilic, thermophilic, cooling, maturation), with final seed germination index (GI) > 95% and significantly reduced E4/E6 ratios, indicating maturity. (2) When kitchen waste (KW) was ≤20%, cumulative GHG emissions slightly increased; KW ≥ 30% led to net reductions, with the 6:4 treatment (A4) achieving the highest decrease (17.44%) in total CO2-equivalent emissions. In conclusion, maintaining KW at 40–50% optimally balances compost maturity and emission reduction, providing a viable strategy for the high-value utilization of urban organic waste and carbon mitigation.