Research On Ecological Treatment System Of Decentralized Domestic Sewage In Rural Area

In recent years,the sewage discharge and the number of pollution sources in rural areas have increased sharply in China.In order to accelerate the construction of ecological civilization,the protection and restoration of rural ecological environment are emphasized while developing economy.In this thesis,combined with the current problems and characteristics of domestic sewage in the local rural areas,some researches on ecological treatment system of decentralized domestic sewage in rural areas are carried out in Yaoba Town of Luzhou City,Sichuan Province.First of all based on the comprehensive literature survey of current research and application status of sewage ecological treatment,the better understanding of the principles,advantages and disadvantages of different type of technological processes were obtained.By the in-site investigation and surveys,some basic data and information on natural,social and economic situations such as topography,climate,hydrology and soil types in the research area were collected for the next design.According to the relevant norms and experience,sampling experiments were carried out on soil,well water,river water and domestic sewage to test the chemical properties of soil and water such as p H value,organic matter,TN?TP?NH₃-N?COD?BOD₅,as well as the physical characteristics such as specific gravity of soil,dry density of soil,saturated permeability coefficient,and also some chemical data analysis were prepared for the construction of ecological treatment system later.Considering the natural,social and economic conditions in the research area,two kinds of ecological treatment systems,i.e.Compound ecological sewage treatment based on slow soil infiltration system and constructed wetland sewage system,were selected for this research.And then the mechanism of action,characteristics,advantages and disadvantages of different technological processes in the two systems were analyzed.Above all,the components,program processes and the main control parameters such as fundamental dimensions,hydraulic loading rate,hydraulic retention time,soil medium and plants grow,the amount of water treated were designed according to the existing specifications and other engineering experience.Then the investment estimation of the project construction was made with reference to the existing market price.In order to evaluate the suitability of the two ecological treatments in Yaoba Town,the index evaluation system is constructed in logical and systematic way by using the method of analytic hierarchy process?AHP?,with the maximization of comprehensive benefits of ecological treatment system as the general objective.The four criterion layers include sewage treatment effect,construction and operation cost,ecological and social benefit,construction and operation management.And then the corresponding indicator layers:removal rate of 6 pollution indicators consisted of TN?TP?NH₃?SS?COD?BOD₅,investment required for daily unit water treatment,annual operating cost,ecological landscape function,leisure and entertainment function,function of science and education,technical difficulty of construction,completeness of the operation management system,difficulty in managing operations are selected for quantitative and qualitative evaluation under each criterion layer.Finally the two ecological treatment systems are evaluated and analyzed based on the constructed index evaluation system.The results showed that the constructed wetland treatment system was more suitable for domestic sewage treatment in Yaoba Town.