Optimal Selection Of Sewage Treatment Technologies And Construction Sites In Town Areas Of Liao River Basin In Jilin Province

The Liao River basin of Jilin province is an important commercial agricultural and industrial base in China,and has an important strategic position.However,due to the small nature runoff,weak self-purification and lack of an effective sewage treatment system in many town areas,the Liao River is heavily polluted and it is difficult to meet the standards of assessment sections.In recent years,proposal and planning of new sewage treatment facilities is urgently needed in towns.Due to lack of funds for water pollution control and low population density in such areas,selecting optimal sewage treatment technologies and construction sites suitable for local characteristics is important issues that need to be addressed simultaneously.The development of sewage treatment technologies has made many treatment options available in towns,but selecting an optimal solution is complicated and multifaceted.This is because the trade-offs between multiple factors need to be comprehensively considered in the decision-making process,such as the distribution of costs and benefits,the environmental impact on the population,ecological risks,etc.,which poses challenges to national,regional and local decision makers.In addition,site selection of facilities is also a vital issue that needs to be discussed,as the rationality of site selection is directly related to the difficulty of construction,operation effect and impact on the surrounding environment and society,etc.Currently,there is a huge subjectivity in watershed water environment planning and management in China,as many people might choose sewage treatment technologies and construction sites based on their intuition or experience.This process will make them lose important information or ignore uncertainties,resulting in waste of resources,poor operation effect,adverse impact on the environment and society and other problems.Selecting optimal technologies and construction sites can maximize the use of existing resources and achieve the most ideal effect,which has become topical issues in the academic circle.In order to resolve those issues,the fuzzy set theory,the AHP,and the TOPSIS were combined as a scientific and effective multi-criteria decision-making model to optimize the sewage treatment technologies in town areas of the Liao River basin in Jilin Province,where the three criterion layers and ten indicator layers were constructed into a set of indicator systems,and the commonly used sewage treatment technologies and their combination technologies were regarded as candidate alternatives.Then the coupled model was applied to Lishu County,Yitong County and Dongliao County respectively.Through scenario analysis and sensitivity analysis,it was found that the indicator of construction costs is critical in this model,as the fluctuation of its weight might significantly affect the optimal selection of a technology.Compared with natural treatment technologies and combination technologies,single small-scale sewage treatment plant technologies are more suitable for those areas.Based on the above conclusions,GIS technology and the AHP were combined as a spatial site selection model for sewage treatment plants in Liao River Basin of Jilin Province.The eight restricted indicators and nine selective indicators were processed by spatial overlay analysis,including the indicators of dominant wind direction and urban stream direction which have not been considered in most existing studies,and then the siting suitability map of this basin could be drawn.The spatial information of ten random existing sewage treatment plants was used to verify the accuracy of the model in the whole river basin,which could also evaluate the location of these sewage treatment plants and then analyzed optimal siting areas of five medium-sized towns lacking sewage treatment facilities by coupling remote sensing images.It was found that this model has high precision and accuracy,and the analyzed siting areas have significant feasibility.Only one sewage treatment plant is located in a restricted area because of the severe social impact on residents,and Huaide Town has the widest suitable siting areas,while Shijiapu Town has limited ones.Through the multi-criteria decision-making model and spatial site selection model,this thesis can effectively combine spatial and non-spatial information,and simultaneously consider economic,environmental and social factors,in order to provide a multidimensional decision support framework for future optimization of sewage treatment technologies and their spatial site selection.This model can also be applied for technology evaluation or siting area analysis in other industries.