Study On Ecological Engineering Technology Of Water Purification In The Inflow Section Of Bajiahe River

Dalian is a resource-based water shortage city,70-80% of urban water supply tasks are undertaken by the Biliuhe Reservoir,whose water quality safety is crucial to the water supply security of Dalian.Bajiahe river is the third largest tributary of the Biliuhe Reservoir.The scale of agriculture and aquaculture in the basin is large,and the pollution sources are large and wide.Limited to the level of economic development and the shortage of sewage treatment facilities,many pollutants are directly discharged into the river without treatment,which poses a potential threat to the water quality safety of the Biliuhe Reservoir.In this paper,based on Bajiahe river,the third tributary of Biliuhe reservoir,the paper puts forward the measures of ecological engineering of water quality purification with regional adaptability on the basis of analyzing the distribution characteristics of pollution sources.The main research results are as follows:(1)There are about 4,800 people in the Bajiahe river basins,and agricultural cultivation and animal husbandry are the main industries.It is found that the annual discharge of domestic sewage in the basin reaches 35040~52560m3,which consumes about 1080 t of chemical fertilizer,about 15.3t of pesticide,about 87.2t of agricultural film and the total amount of major pollutants that enter the water body are as follows: the total amount of TN is 114.99~116.04t/a and that of TP is 30.05~30.38t/a.In the absence of necessary facilities for the treatment of pollutants in the watershed,most of the pollutants entered the Biliuhe Reservoir in the untreated condition.Water quality sampling analysis found that the water body in the study area was generally in an eutrophic state,and the overall water quality was inferior to V.(2)The submerged dam project utilizes drowning water effect to form surface flow wetlands in front of the dam.It is a technical means that can be used for water pollution treatment with small pollution and small single flow rate.If necessary,the purification effect can be further enhanced by increasing the series number or planting wetland plants.The measured water quality in the entrance area of the Bajiahe River shows that the water quality of the area is eutrophic,but the concentration of pollutants is not high.The width of the river reaches more than 200 m,and the average annual runoff is only about 0.28m3/s.Also,the single-wide flow rate is small.It is suitable for the use of multistage dam projects for sewage treatment.Taking the surface water of Class III as the water requirement,the water purification project planning in the study area was studied.The study found that through the construction of three-stage dams,a three-level surface flow constructed wetland with an area of about 416,100 m2 will be formed in front of the dam.The total hydraulic retention time is about 13.04 d.(3)Model analysis found that the water quality could meet the three types of surface water quality standards under the design of the water quality.The total investment of multistage dams in Bajiahe River is about 4.8 million yuan.In order to quantify the comprehensive benefits of multi-stage dam projects,four potential indicators,including pollution degradation,biodiversity,water supply and research and culture were selected to construct the dam project.The comprehensive benefit analysis system is applied to the benefit analysis of the Bajiahe river mainstream multi-stage dam.The analysis found that the completion of the project will bring about 1.249 million yuan in ecological,environmental,and social benefits each year.