| With the acceleration of industrialization and urbanization,China is facing serious water pollution problems.In recent years,with the joint efforts of the government society,China's water pollution control and water environment treatment has achieved inspiring results.However,the stringent trend of sewage discharge standards and the increasing intensity of sewage treatment have also led to intensive discussion of environmental sustainability of sewage treatment.In order to deepen the understanding of this issue and provide scientific management advice,from the perspective of global sustainable development,a major scientific research need is to build a scientific and rational environmental impact assessment method.Life Cycle Assessment(LCA)has experienced 30 years of rapid development,but there are many methodological limitations in the application of LCA in the field of sewage treatment.In the field of wastewater treatment,the limitations of LCA extracted in this study mainly include:(1)there are usually multiple LCA built-in methods to choose from,and different built-in methods usually lead to different assessment results;(2)the results of LCA usually have the characteristics of "regional generalization".That is,the environmental impact represented by the assessment results does not represent the direct impact of certain pollutant to a certain region;(3)LCA results are usually interpreted by a one-way information flow mechanism,which is generally not conducive to the widespread acceptance and recognition of the results of LCA;(4)LCA is a single-threaded evaluation method,which can only ouput the evaluation results through its internal evaluation mechanism.But when appropriate methods are sought to improve the sewage treatment system,which is usually not conducive to the wide acceptance and recognition of the evaluation results.To solve the above problems,this study constructed an integrated decision-making system with LCA as the ontology and multiple scientific methods,namely HIT.WATER system.This paper first identified the key initial elements for the construction of HIT.WATER system by comparing the research methods of different LCA methods.Methods of comparison are the internationally used LCA method(CML)and the LCA method designed for the China(e-balance).Based on the case study of the sewage treatment plant,the results show that scenario 4(which represents the direct discharge of sewage without treatment)has the minimum total environmental impact under the CML method,but the highest total environmental impact in the e-balance method.The main reason for the difference is that the contribution potential of COD to the total environmental impact is extremely low under the CML method,but it is a key factor in the e-balance method(accounting for 67.4%).Due to e-balance method of COD is defined as an independent from other environmental impact categories of environmental directory,considering the COD is one of the main pollutants in China's water pollution problem,this also shows that in the use of LCA to evaluate China's sewage treatment measures or related cases,should consider China mainly exist in specific period of time the specific ecological environmental requirements.Finally,when building the HIT.WATER system,the COD environmental directory should be taken as the starting element.This study demonstrated the construction process of HIT.WATER system by coupling LCA,WATER quality model,statistical analysis method and environmental economics method.Firstly,within the existing LCA framework,this study established a LCA characterization model system with COD as an independent environmental directory,and elaborated the establishment principles and methods of this system.At the same time,this study coupled the water quality model and COD characterization model,so that HIT.WATER system has the function of dynamic output.Further,the joint LCA and environmental economics model(the joint analysis method)was established to enable HIT.WATER system to break through the information flow barriers existing in the LCA result interpretation mechanism and established a two-way LCA result elaboration mode.Then,the Plackette-Buraian method was introduced into the system,which enabled the modular case analysis and scheme selection.Finally,the water quality of receiving waters protection objectives cover in HIT.WATER in the system(as a tradeoff alternatives to the environmental benefits of the constraint conditions and the environment load),and to deduce the upgrading urban sewage system of the three scenarios: based on command-control of sewage plant upgrade scenario,based on receiving water quality protection target inverted sewage factory upgraded scenario,based on the confluence point source,non-point source pollution synergetic control in drainage system of upgrading scenario.Finally,in the way of case analysis,this study has realized three functions of HIT.WATER system: dynamic LCA result output,modular case analysis and stakeholder participation decision-making analysis,selection and optimization of urban sewage system upgrade and transformation scheme.According to the results of the cases that have been obtained,this study found that :(1)The environmental load comparison between discharge standards of sewage plants is an unsteady process affected by many factors,so it is difficult to reach a certain conclusion about "which standard is better".(2)When seeking an effective scheme for the upgrading and transformation of urban sewage system,the collaborative treatment of point source pollution and non-point source pollution should be considered.Therefore,while strengthening the treatment of point source pollution to improve the standards for sewage plants,the construction of gray facilities and green facilities should also be considered for the treatment of non-point source pollution.(3)The adoption of gray facilities plan,compared with the gray-green infrastructure solutions,the water pollution control capacity relative to the sensitivity of the receiving waters from the net ability was nearly 70 times higher.This means that when receiving waters self-purification ability declined slightly,with gray infrastructure solutions may not be able to meet only the downstream water body protection goals;(4)The combination of grey-green facilities not only has a more stable effect on water pollution control,but also can reduce the greenhouse gas emissions of the entire urban sewage system;(5)For the upgrading and reconstruction of urban sewage system,if the self-purification capacity of natural ecosystem to pollutants can be reasonably utilized,the life cycle environmental load caused by the construction of engineering facilities can be reduced. |
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