Dry-weather Sewage Interception Effect And Countermeasures Of Separate Storm Sewer Systems In Shanghai

The discharges from separate storm sewer systems in the dry weather do great harm to receiving water in Shanghai. To solve this problem, Shanghai has built a lot of dry-weather sewage interception infrastructures in the storm sewer systems. These interception infrastructures have reduced a large mount of dry-weather sewage, while at the same time, they have brought heavy shock load which makes some of the receiving water body deterioration badly. All these have brought bad impacts to the environment and society.In this paper, characteristics of the dry and wet weather pollution loads were monitored from two typical separate storm sewer systems in Pudong District. Combined with the research results found by our team before, the differences of the discharges from the separate storm sewer systems before and after dry sewage interception were compared, and the influences of interception to the sewer disposals and the reason of the shock load were analyzed. The first flush phenomenon and settling characteristics of the discharges were also studied for both systems in two different operating modes: the interception mode and the flood control mode. On this basis, the long-term average operating efficiency of flow-through sedimentation storage tank was calculated using the probabilistic analysis methodology. Finally, a series of suggestions were put forward for optimizing the operation and management of separate storm sewer system.The study of the characteristics of the discharges before and after dry-weather sewage interception showed:â‘ Because of the influence of the sewer sediments, the COD,SS,TP concentration was much higher in the interception mode both in dry and wet weather outflows. And the impact of dry sewage interception was positively related to the degree of illicit connections to the storm sewer system; the changes of NH₃-N concentration were more related to the TN load in the raw sewage that was illicitly connected.â‘¡In large storms, the influence of interception to the discharges was most obvious because more pumps were turned on and the scour of the pipes was more violent. The results of the first flush effects for the storm sewer systems wet weather flow showed that:â‘ The typical storm sewer systems in Pudong area showed no first flush effects or just slight first flush effects.â‘¡The b parameters of SS after interception were all increased and larger than 1, which indicated that after interception, SS showed more obvious negative first flush because of the sewer deposits.Researches on the settling characteristics of the discharges from the storm sewer systems had the following results:â‘ For dry-weather discharges, the settling characteristics of TP , TN was poor, while of COD and SS were comparatively good.â‘¡For wet-weather discharges, the settling characteristics of both systems were quite good under both operation mode. While it's better under interception operation mode than flood control operation mode, especially for SS.â‘¢The average sedimentation rate of Jingdong pump station in interception and flood control mode were: 12.2cm /min, 8.87cm /min respectively, the related results for Jinqiao2# were 10.47cm /min and 9.12cm /min. They were close to the sedimentation rate of the combined systems overflow reported aboard and providing possibility of using the flow-through sedimentation tank.Analysis of the dry-weather sewage interception effect and the studies of improving operation of separate storm sewer systems in Pudong District showed:â‘ The dry-weather sewage interception infrastructures have reduced both the flow and pollutant load from the storm sewer system in dry weather.â‘¡The flow-through sedimentation tank may be a good choice to control the pollution of storm sewer systems.â‘¢Cleaning of the sewer sediments, especially for some defected pipes may be an effect way to reduce the pollutant load under interception operation mode.â‘£Integrated management of sewer systems, improvement of interception infrastructures and selection of a rational interception capacity were important issues which need further study and discussion.