Life Cycle Assessment Of Green Infrastructure Facilities Of Sponge City

In recent years,under the influence of rapid population growth,accelerated urbanization and global warming,non-point source pollution,urban waterlogging disasters,water shortage and the heat island effect have become very prominent environmental problems.Research and implementation of a reasonable stormwater management system are essential for the sustainable development of the city.Construction of sponge city is very important to the development of cities in China.The sponge city project has been rapidly applied and accepted in many pilot cities in the past three years,but most of the related researches remain on the improvement effect and economic benefits of water quality and water quantity.Life Cycle Assessment(LCA)method can be applied to sponge city project to evaluate its environmental advantages and disadvantages as well as environmental impacts at different stages of its life cycle.At present,domestic related research mainly focuses on sewage treatment technology,design scenarios for a single green infrastructure,etc.,while LCA research on sponge city with multiple green infrastructure combinations in actual cases is less.This study uses LCA to obtain the quantitative analysis of environmental impact of sponge city,which provides support for decision makers to choose the construction method of stormwater management system.This study takes one of sponge city demonstration project as a specific case,which located in the public service platform in Guangming District in Shenzhen,and chooses three green infrastructures: permeable pavement,green roof and sunken green space as the research objects to carry out LCA research.SWMM(Storm Water Management Model)model is utilized to simulate the storm water process for the scenario composed of three kinds of green infrastructure and the hypothetical scenario of gray infrastructure as a reference.The simulated runoff coefficient value is the key input data for the subsequent LCA calculation.Futhermore,combined with the current situation,literature and planning data of the research area,the material energy consumption lists of different facility systems at several stages of construction,operation and abandonment are constructed.After completing the checklist,Gabi software is applied to build a full life cycle model,and the environmental impacts of green infrastructure and gray infrastructure are compared and analyzed comprehensively.The specific conclusions of this research area include:(1)During the 30 years of operation,the total environmental load emission of green infrastructure has decreased by 24% compared with that of gray infrastructure.The category with the largest proportion of environmental emissions of both is fossil resource consumption.(2)In quantitative analysis,environmental impact indicators are divided into three categories: ecosystem impact,human health impact and resource consumption.In terms of ecosystem impact,the total impact of green infrastructure on the ecological environment is much smaller than that of gray infrastructure,of which the climate change impact value of green infrastructure is only 4.29% of gray infrastructure;in terms of human health impact,the toxicity to the human body caused by green infrastructure is also less than that of gray infrastructure;in terms of resource consumption,the overall consumption of green infrastructure is higher than that of gray infrastructure.Among them,the land occupation of green infrastructure is about 58 times that of gray infrastructure.(3)In view of the normalized total environmental impact of three green infrastructures,the environmental impact of permeable pavement per unit area is the greatest,which is 1.8 times and 7.6 times that of green roof and sunken green space respectively.The construction stage of permeable pavement and green roof contributes the most to the total load of their whole life cycle,while the transportation stage of sunken green land contributes the most to the load.The operation stages of the three facilities have noticeable improvement effect on water eutrophication,and the use of green plants in green roof and sunken green land can alleviate climate change.(4)Sensitivity analysis of runoff coefficient shows that the construction of sponge city facilities under the condition of low runoff coefficient enhances the improvement effect of green infrastructure on freshwater eutrophication and seawater eutrophication,and reduce the toxicity of human non-carcinogens produced by the environment.This study compares the environmental impact indicators of different categories of green infrastructure and gray infrastructure in the whole life cycle,and shows the advantages and disadvantages of green infrastructure compared with gray infrastructure in terms of environment intuitively.Besides,contribution proportions of three kinds of green infrastructure in different stages of the life cycle are analyzed respectively,and the load contributions of construction,transportation,operation and abolishment stages to different environmental indexes are quantitatively analyzed.This study will have the guiding value for environmental impact control of sponge city engineering projects.