| The problem of urban water pollution in China has existed for a long time.The main point source pollution is drainage pipe network point source pollution and caused by insufficient treatment capacity of sewage treatment facilities.As the scale of urban sewage treatment facilities increases,the problem of end-of-pipe sewage treatment has been basically solved,and point source pollution of the drainage pipe network has become one of the main pollution sources of urban water.By investigating the drainage networks of eight cities in northern,southern,eastern and central regions of China,it was found that the combined pipeline network overflows in rainy days,the downstream sewage treatment facilities overflows,and the and the direct discharge of non-stormwater entries into storm drainage system are the current source pollution of the drainage pipe network.It is also the main cause of black and odorous water bodies,and all regions mainly use interception to solve point source pollution.At present,the traditional weir,trough and weir-tough interception wells have been rarely applied due to the large deviation between the design calculation results and the actual results,,and the difficulty of later well reconstruction.In practice,it is necessary to calculate the interception rate in overflow state to determine the amount of water delivered to the downstream structure and the interception effect.At the same time,there is often a mismatch between the treatment capacity of sewage treatment facilities and the interception volume.And there is insufficient basis for selecting the interception ratio,and there is no parameter to visually show the effect of interception.In addition,according to the problems and needs in various regions,the operation and maintenance of the closure wells is currently chaotic,and there are also no provisions for related facilities such as anti-backflow and garbage interception.Therefore,in terms of the design of the interception system,according to the sewage treatment facilities remaining treatment capacity of the dry season,this paper proposes calculation methods for parameters such as the interception ratio n,the storage volume V,the overflow frequencyαand the overflow control rateβunder different conditions.At the same time,the technical,economic and construction aspects of the two interception schemes,such as increasing the weir height,trough depth,and diameter of the intercepting pipe to directly increase the interception ratio and increasing the storage facility to indirectly increase the interception ratio.In terms of design calculations,it has verified through experiments that the calculation formula of intercepting weir well and intercepting trough well are consistent with the calculation results of“Specification for design of combined sewage intercepting well CECS 91:97”,when the combined flow rate is large.the calculation formula of intercepting weir-trough well in specification should be modified:the depth of trough（H2）calculated by the specification needs to be added with a correction factor k’,（the high of weir）H1’=H1/k’,if H1/H2≤1.3:k’=1.85-0.001×（H2-400）;if H1/H2>1.3:k’=1.55-0.0018×（H2-400）.Since the“Specification for design of combined sewage intercepting well CECS 91:97”only calculates the situation for all interceptions,In a state of overflow,he optimal model of the relationship between the interception rate and the combined flow of the intercepting weir well is the binomial model,and interception rate decreases rapidly and then stabilizes with the increase of combined flow rate.Under the same combined flow,interception rate has a positive linear relationship with the weir height and weir depth.The larger the combined flow,the smaller the slope.According to the above relationship,the calculation method of the interception rate in the overflow state of the interception well is constructed.Finally,provide a comparison plan for design or reconstruction,with the increase of the combined flow of intercepting weir well and intercepting trough well,the benefits of increasing the height of the weir or the depth of the trough will become less and less.In the case of large combined flow on a rainy day,increasing the weir height or the depth of the trough will not increase large interception rate. |
