| Non-point source pollution is one of the major sources of pollutants in most water body in China and all over the world. In 2012, the total phosphorus and total nitrogen pollution from non-point sources accounted for 68.7% and 36.8% respectively of the composition of pollutants into the Dianchi Lake. Pollutant source control and interception are effective means to reduce pollutants into the Dianchi Lake. A large-scale ring main sewer tunnel has benn built along the Dianchi Lake. A main sewage interception project framework has been formed based on area interception, rivers interception, towns and villages interception and ring main sewer tunnel, and it intercepts pollutants from the source control to interception at the end in the Dianchi Lake basin. But the rainfall-runoff process and quantity & quality rule of rainfall runoff in the collection process are not clear, and the ring main sewer tunnel project lacks appropriate supporting facilities, so the surrounding polluted rainfall runoff can not be collected into the ring main sewer tunnel effectively. The comprehensive pollution control performance of the tunnel can not be put to good use.The study area of this thesis is the rural area between Ma Liao River and Luo Long River along the east coast of Dianchi Lake. This region has a complete system of agricultural irrigation ditches. Part of semage should be cut off into the ring main sewer tunnel via these interceptors built at the junction of the agricultural irrigation ditches and the ring main sewer tunnel. These semage will be ultimately sent to a sewage treatment plant and be discharged into water body after treatment reaching the standard. But the rainfall-runoff process and quantity & quality rule of rainfall runoff in the collection process have not been understood scientifically, so these valves in these interceptors can not be controlled effectively and they are always set off state. The surrounding polluted rainfall runoff can not be collected into the ring main sewer tunnel effectively. This thesis studied the rainfall-runoff process feature and quantity & quality rule in this rural area based on the measured rainfall-runoff data of two typical irrigation ditchs selected in the study area. The author thought that selecting Liquid Level-Time combination control mode to control these interceptors automatically was appropriate. This thesis obtained the reasonable value of Time in the Liquid Level-Time combination control mode with the SWMM model set up with measured rainfall runoff data. At the end of this thesis, interception efficiency of the main pollutants were also analysed under the seting conditions. The main conclusions of this thesis are as follows:1) In the study area, the major pollutants in rainfall runoff of flower greenhouses region are TP, NH3-N and SS, while the major pollutants in rainfall runoff of vegetable greenhouses region are TP and SS. These pollutants should be the main contaminants that the ring main sewer tunnel collects.2) Whether it is flower greenhouse area or vegetable greenhouses area, the average concentration of major pollutants in the early rainfall runoff is higher than that in the late rainfall runoff. In the first 30% of the rainfall runoff, the load of TP, NH3-N and SS are 31.76%~40.21%, 37.32%~44.56%, and 33.02%~45.45%, respectively.3) The ring main sewer tunnel should collect the early rainfall runoff, and selecting Liquid Level-Time combination control mode to control these interceptors automatically is reasonable.4) Under the current condition, if all the intercepting wells have been built at the terminal of all agricultural irrigation ditches within the study area and these valves are opened wide, the ring main sewer tunnel could collect over 45% of the rainfall runoff when the rainfall return period is less than 4 years(rainfall is 49 mm and rainfall duration is 2 hours), relying solely on the discharge capacity limit of intercepting pipeline.5) The liquid level parameter “H” should be determined by the actual level of irrigation ditches in sunny days, and the closure time parameter “T” should be 100~120min. The ratio of the amount of water is 28%~42%.6) In the typical design rainfall conditions, when the T is set to 110 min, the interception efficiency of pollutants will increase with the rainfall return period positively. When the rainfall return period is more than 0.5 year, water interception ratio is more than 33% and SS, NH3-N and TP interception proportion will exceed 37.2%, 39.6% and 36.7%, respectively.7) In the typical rainfall years, when the T is set to 110 min, pollutants interception efficiency will increase with the annual precipitation positively, and interception ratio of water is more than 30% steadily, and interception ratios of pollutant load are more than water interception ratio. |
PDF Full Text Request