Research On Pollution Receiving Capacity And Its Improvement Of South South Section Of Yi Tong River

This thesis takes the southern section of Yi tong River in Changchun City as the research object.Combining the characteristics of river pollution,study the pollution holding capacity of COD,NH₃-N and TP in natural rivers.The pollutant degradation coefficient and the designed flow rate are important parameters of the pollution holding capacity model.The two parameters are obtained and brought into the pollution holding capacity model,obtained that the natural water body has no pollution-holding capacity,design aquatic plants to purify water quality experiments,and study the improvement of rivers'pollution-holding capacity through aquatic plants.The main research contents are as follows:Six monitoring sections were set up on the southern section of Yi tong River,and the degradation coefficients of COD,NH₃-N,and TP were measured using the two-point estimation method based on the measured data.Obtained the degradation coefficients of COD,NH₃-N and TP during the dry period?4?5?10?.When the water temperature is between 4.55-12.0?,the dissolved oxygen is between 8.10-11.3 mg/L,and the p H is between 7.12 and 8.87,the value ranges are respectively 0.051-0.153d^-1,0.119-0.201d^-1,0.024-0.031d^-1,During the wet season?6-9?,when the water temperature is between10.3-20?,the dissolved oxygen is between 6.13-9.4mg/L,and the p H is between 6.37-8.16,the value ranges are 0.114-0.210d^-1,0.217-0.339d^-1.0.034-0.055d^-1.Two methods,the long-series historical data method and the water balance method,are used to calculate the design flow.Using the long series of historical data method,the design flow rate in the wet period under 50%guarantee rate is calculated to be 3.19m³/s,and the design flow rate in the dry period is 1.39m³/s;the design flow rate in the wet period and the dry period simulated by the water balance method are 3.59 respectively m³/s,1.52m³/s;therefore,the long series of historical data is similar to the results of the water balance method.According to the calculation of the pollutant degradation coefficient and the designed flow rate,and then based on the one-dimensional model of the river,the subsection summation method is used to obtain the COD,NH₃-N and TP pollutant holding capacity of the south section of the Yi tong River in Changchun City during the high water period-31.97g/s,-1.10g/s,-0.22g/s;the dry periods are-5.98g/s,-0.06g/s,-0.08g/s,respectively.Three experiments were designed for the reed group,the cattail group,the reed group and the cattail combination.The reed group has a better purification effect on COD and TP.The removal rate is the highest when the hydraulic retention time is 4d and 5d,reaching 37.5%and 47.1%respectively.The removal rate of NH₃-N in the cattail group reached the highest 45.8%on the 4th day,and the purification effect of the reed and cattail mixed group on COD,NH₃-N and TP was between the reed group and the cattail group.Although the mixing of two plants has a weaker purification effect on a single indicator than a single species,the mixed species of two plants has a significant comprehensive purification effect on multiple pollutant indicators.At the 5th day,each pollution indicator achieves the best purification effect,the removal rates of COD,NH₃-N and TP were 36.3%,44.5%,46.9%,respectively,and tended to be stable after 5 days.