| The defining method of initial rainwater runoff directly affects the collection and control effect of polluted rainwater.It is of great practical significance to carry out the determination of initial rainwater runoff and the research on the collection and control mode of initial rainwater runoff in chemical industry areas for the prevention and control of runoff pollution risk in chemical enterprises.Based on the related research topics of Shanghai Chemical Industry Zone,this paper carried out the enterprise questionnaire survey and field sampling monitoring,and summarized the early rainwater runoff determination methods into time method,water method and water quality method from three dimensions of rainfall time,rainfall depth and rainwater runoff quality.According to different determination methods,this paper constructs the “initial rainwater runoff collection and control modes based on rainfall time / rainfall depth / runoff water quality”(Time Model,Depth Model,Water quality Model),and tries to systematically analyze each mode from the perspective of runoff collection and feasibility.Based on the applicability of each model and the whole process control of rainwater,the optimization scheme is put forward to provide technical support for the prevention and control of early rainwater runoff pollution in chemical enterprises.The main research conclusions and results are as follows :(1)We carried out on-site sampling of initial rainwater runoff for typical enterprises in Shanghai Chemical Industry Zone.The monitoring data showed that the peak concentration of pollutants in initial rainwater runoff was mainly between 10 min and 20 min.After 30 min,the concentration of pollutants was basically stable,and different indicators and different regions were different.Based on the online monitoring data of rainwater runoff water quality of an enterprise in the park,the water quality of rainwater runoff under different rainfall depths was explored.When the daily rainfall depth is less than 30 mm,according to the 《Shanghai Municipal Integrated Wastewater Discharge Standard 》 secondary standard,the frequency of COD concentration exceeding the standard is as high as 70 %.When the daily rainfall depth is greater than30 mm,the abnormal frequency is greatly reduced and the water quality is obviously alleviated.According to the actual monitoring data analysis,it is appropriate to select the rainfall of 15 min ～ 30 min in the early rainfall or 20 mm ～ 30 mm in the early rainfall as the initial rainwater runoff and collect it,which can effectively reduce the concentration of pollutants in surface rainwater runoff.(2)The difference of initial rainwater collection in each mode is related to rainfall intensity.When the rainfall intensity is medium and small rain,the difference of initial rainwater collection is: Depth Mode > Water Quality Mode > Time Mode.We calculate the initial rainwater collection under the rainstorm intensity according to the unified short-duration rainstorm intensity formula in Shanghai.When the return area is two years,the difference of initial rainwater collection is: Water Quality Mode > Time Mode > Depth mode.The initial rainwater runoff classified collection and control mode in the chemical industry park will be affected by many factors such as weather factors,underlying surface pollution degree and technical requirements.These influencing factors and initial rainwater treatment costs will limit the practical feasibility of each mode.(3)The results of water quality data analysis show that the time model has good implementation effect in reality,but when the rainfall intensity is small,it is difficult to collect all the polluted rainwater in 15 min ～ 30 min.The depth model can collect all the rainwater runoff at 30 mm rainfall depth,effectively reduce the risk of runoff pollution,and the practical operation is feasible.The water quality model can effectively control the initial polluted rainwater runoff by monitoring the conventional water quality indexes such as p H and COD.However,considering the delay of online monitoring results,monitoring technology and rainwater treatment cost,the current model requires high operation.In addition to the above three modes,the park enterprises have the phenomenon of initial rainwater runoff collection temporary storage and dilution discharge.The water quality monitoring data of enterprise rainwater outlets show that the model has a certain risk of rainwater runoff pollution,and it is inconsistent with the requirements of the national standard “treat the initial polluted rainwater as production wastewater”.(4)In order to further highlight the principle of “discharge water quality management”,enterprises should adopt the combination of classified collection control mode and on-line monitoring of rainwater outlets to implement efficient differentiated management of early rainwater runoff in chemical areas,and realize the three-level whole process control of “source interception-process collectionend water quality supervision”. |
