Urban-industrial symbiosis practices in Tokyo Metropolis and the indication of carbon emissions reduction and environmental benefits

To enhance the efficient utilization of urban resources and optimize regional metabolic networks, the concept of Urban-industrial symbiosis (UIS) has been introduced as a strategic approach within the waste management sector. However, current assessments of municipal solid waste management often overlook the potential environmental burden associated with products. Therefore, this study, using Tokyo Metropolis as the case study area, integrates the Input-Output (IO) model, Emergy Analysis, and Life Cycle Assessment (LCA) to comprehensively evaluate both the direct hazards and the implicit environmental burdens of waste management. This integrated approach addresses the limitations of individual assessment methods, providing a more holistic understanding of the environmental and ecological impacts of urban waste management. The results show that the contribution rate of carbon emissions from upstream sectors to the waste management industry was 0.09 % in 2011, which decreased to 0.06 % in 2018. In 2011, the carbon emissions reduction from the waste management sector accounted for 40.59 % of the total carbon reduction gains, which increased to 58.69 % in 2018 (increasing at a rate of 1.57E+05 tCO_2e/yr). Furthermore, all of the implementation of circular economy practices in Tokyo metropolis saved 7.44 × 10²⁸ sej emergy in 2011 and 2.28 × 10²⁸ sej emergy in 2018, respectively. And the environmental service required for the reduction of CO_2e emissions in Tokyo metropolis due to its circular economy practices was 3.94 × 10¹³ in 2011 and 3.90 × 10¹³, in 2018. Indicating the significant benefits of resource and emergy conservation. Additionally, this study found that from an emergy-saving perspective, recycling materials such as urban sludge and sand exhibits greater environmental emergy-saving benefits, while from a carbon emission reduction perspective, recycling plastics, paper, and glass show greater carbon benefits. Based on these findings, the research proposes different policy recommendations for waste recycling.