Life Cycle Environmental Assessment Of Three Urban Drainage Systems For First Flush Pollution Control

In recent years,the first flush pollution control in urban areas has increasingly become an important issue in the urban drainage field.Control strategies such as separated drainage system with interception,on-site treatment of initial rainwater and LID measures have been put forward successively,and more and more applications have also been obtained in China.Different types of urban drainage systems have been formed,resulting in a certain effect of initial rainwater pollution runoff control.These drainage systems will inevitably use a certain amount of materials,chemicals or energy from construction and operation to abolition stage,resulting in widespread and lasting environmental impacts.Life Cycle Assessment(LCA)is used to evaluate the life cycle environmental impact of different types of urban drainage systems,which can identify and quantify the environmental load in the whole life cycle process effectively,compare the differences in the environmental impact of different types of drainage systems,and provide theoretical basis for designers and environmental decision makers.It has important theoretical and practical values,and is also an important means to deal with the challenges of sustainable development and the application of life cycle analysis.Based on the criterias and technical frameworks in ISO 14040 and ISO 14044,it determined three types of drainage systems based on the purpose of initial rainwater pollution control—separated drainage system with initial rainwater terminal disposal(S1),separated drainage system with initial rainwater storage and treatment(S2),completely separated drainage system with LID measures(S3)—as research objects,and the drainage systems required for 1 year on the 1km~2 service areas as functional unit.According to industry design standards and similar engineering cases,these drainage systems were designed.Rainwater runoff conditions were simulated by SWMM model and drainage system data lists were calculated.SimaPro software which was recognized internationally,ReCiPe impact assessment model and databases combined with China LCI developed by Beijing University of Technology and Ecoinvent were used to simulate the environment impacts of three drainage systems.Characterization,normalization,damage assessment and weight assessment respectively were used to compare the environmental impact of the three drainage systems and analyze the order of importances environmental issues.The significant aspects of environment problems were identified through the contribution analysis.Sensitivity analyses of the evaluation model,service period and the scale of WWTP were carried out to comprehensively analyze the load and benefit generated by the drainage system on the environment.The results showed that:1)S1 system has the greatest life cycle environment impact,and the S3 system has the smallest impact.Compared with S1 system,S3 system can reduce the life cycle environmental impact by 15%,and can reduce the life cycle environmental impact by 3%compared with S2 system;2)Marine ecotoxicity,freshwater eutrophication,and marine eutrophication are the most important environmental impact type of the drainage systems;3)Among the three links of construction,operation and dismantling stage,the operational stage contributes most to the environmental impact and the impact of the dismantling stage is minimal and insignificant;energy consumption,sludge treatment and tail water discharge in treatment system operation stage and the use of steel and cement in construction stage are the most important aspects for environmental impact;extending the service periods of each unit and increasing the scale of the WWTP would all reduce the environment impact of the drainage systems.