Indicator-system Based Comprehensive Assessment Of Urban Wastewater Reclamation And Reuse Alternatives

With the rapid development of urbanization,water shortages have occurred in many regions of the world.Urban wastewater recycling has received increasing attention,and related projects in many cities in China are also increasing.However,although China has already issued standards for urban wastewater recycling and even some cities have issued their own technical guidelines,the design of urban wastewater recycling projects still relies mainly on the personal experience of designers with their personal experiences and subjective judgements.Restrained in technical side,the wastewater reclamation and reuse planning or design is difficult to be comprehensive.It has been found that wastewater reuse has potential environmental and health risks and has impacts on sustainability.It is difficult to achieve the multiple objectives of the project if it is solely focused on the technical design.This study is intended to establish a set of indicator system and the corresponding comprehensive assessment method for screening various wastewater reclamation and reuse alternatives so as to achieve a comprehensive assessment and optimization of the scheme and provide support for designers and decision makers.Based on the review of urban wastewater recycling and related assessment research,this study analyzes the influencing factors of urban wastewater recycling project,and constructs a set of indicator system including four criteria and 15 indicators.And a network analysis method is proposed.The comprehensive assessment model and case study of the Chongqing Yuelai wastewater recycling project.The main results achieved are as follows:The indicator system for the wastewater recycling project,including the target layer,the criterion layer and the indicator layer.Taking the rationality of the wastewater recycling project as the target layer,the criteria layer includes four criteria: technical suitability,health risk,economy and environmental friendliness.The indicator layer includes 15 indicators: the integration with rainwater utilization and the rationality of the reclaimed water treatment plant(station)site,site design compactness,process condition adaptability,multi-purpose accessibility,pollutant removal efficiency,transmission and distribution system reliability,pipe network water quality stability,operational management suitability,reclaimed water plant safety risk,worker exposure risk,public exposure risk,cost-benefit ratio,life cycle environmental impact,and operational noise.A comprehensive evaluation method for urban wastewater recycling design scheme was constructed.Including the use of analysis network process combined with expert scoring method to determine the relative weight of each indicator,and put forward the definition,use purpose and calculation method of each indicator,including the degree of integration with rainwater utilization,rationality of reclaimed water treatment plant(station)site,and adaptability of process conditions Four indicators such as operational management suitability were used for qualitative assessment.The reliability of the transmission and distribution system and the water quality stability of the pipeline were analyzed by EPANET software for hydraulic and water quality simulation respectively.The public satisfaction benefit indicator in the cost-benefit ratio was based on the willingness to pay questionnaire.The life cycle environmental impact is evaluated by SimaPro9.0 software for the construction,operation and scrapping of the project.The remaining indicators are quantified according to their definitions.In order to standardize the quantitative results of each indicator,the relevant literature was consulted to determine the evaluation criteria for each indicator.Finally,the weights of each indicator are multiplied by the standardized scores to obtain a comprehensive assessment score for the wastewater recycling project,and the scheme is comprehensively assessed according to the determined assessment level.Combining the Yuelai wastewater recycling scheme,the weight analysis of each indicator shows that the technical suitability weight is up to 45.06%,the economy is 28.51%,and the environmental friendliness and health risk are less.They were 13.27% and 13.15% respectively.However,the comparison of the weights of various indicators shows that the cost-benefit ratio has the largest weight and the relative weight of life cycle environmental impact,worker exposure risk,and public exposure risk is larger than that of transmission and distribution system reliability and site design compactness,etc.The result indicate that the technical economy has the greatest impact on the scheme,but the environmental friendliness and health risks cannot be ignored in the assessment.According to the constructed indicator evaluation model,the two design schemes of the Yuelai Sewage Recycling Project were compared and selected.The results show that the scheme 1 of the Yuelai Sewage Recycling is 80.969 points and the scheme 2 is 82.486 points.The assessment grades of all the design projects are all good,and the scheme 2 is relatively good.However,the design of the supporting pipe network of the second project is poor.It is recommended that the pipe network of the second project be optimized by high and low pressure water supply.Through the comprehensive assessment of the Yuelai wastewater recycling project,it is shown that the indicator system and assessment model established in this study are feasible and operable.