Assessment of urban symbiosis effect on urban metabolism based on energy flows analysis and life cycle assessment

 Cities are responsible for more than 60 percent of global energy consumption and three-fourth of world greenhouse gas emissions. Industrial and urban symbiosis can be an effective solution for resource recycling and energy... [ view full abstract ]

 Cities are responsible for more than 60 percent of global energy consumption and three-fourth of world greenhouse gas emissions. Industrial and urban symbiosis can be an effective solution for resource recycling and energy conservation. Numerous studies (eg., Kawasaki, Japan) have verified the greenhouse gas emission reduction and economic benefits of industrial and urban symbiosis. However, the energy exchange between waste management and urban energy system and efficient cascade use of the energy are seldom taken into account. In fact, the coupling effect of urban symbiosis on the urban metabolism process needs to be further investigated.   

 In this study, we propose and assess an urban symbiosis network by integrating the biomass power plant, the MSW treatment and district heating system. The purpose is to optimize symbiosis network as well as operational parameters (technology and scale effect etc.). In the proposed symbiosis network, biomass such as food waste, sewage sludge and waste woods are used to generate electricity, and the residues from the fermentation process are burned in the incinerator to minimize the amount of final disposal amount. On the other hand, heat from incinerator and biomass power plant is used in residential and commercial area through a district heating system. Moreover, the proposed symbiosis network improves the exergy efficiency through combined heat and power system and cascade use of energy, such as high pressure steam is supplied to industries, low temperature hot water is used in district heating. 

Tokyo Metropolis and Shanghai were selected as case areas. After forecasting the potential of heat supply and demand, feasibility analysis was applied to calculate the amount of final heat utilization amount for district heating. Energy flow analysis was applied to quantify the inter-flows and energy saving benefits of the symbiotic network, and the energy recovery efficiency was calculated. Furthermore, environmental impacts such as global warming impact were evaluated with life cycle assessment and carbon footprint index. 

 The result showed that, the renewable energy utilization and energy recovery efficiency increased by combining biomass power plant and incinerator. The proposed urban symbiosis network and energy cascade use generated significant energy saving benefits, at upstream fossil fuel production process and downstream waste disposal within urban metabolism. The system also showed a great potential of carbon reduction, which contributes not only to the recycling society, but also to the urban energy system.