Keywords: 
• separated drainage pump station /
• illicit connections /
• first flush effect /
• sewage discharge /
• event mean concentration

Abstract: The quantity and quality of sewage discharge from Z pump station of typical separated sewer system in central area of Shanghai was investigated and analyzed during rainy days. Basing on the drainage system characteristic， pump station operation and site monitoring， the paper drew the following conclusions.(1)The higher frequency sewage discharge from Z pump station was mainly caused by illicit connection of pipe network system， the high water level operation and pre-evacuation station before rainfall etc. (2)The pollutants EMCs were different in various types of rainfalls. Influenced by the sewer sediments， soluble organic pollutant concentration reduced with the increase of rainfall. However， particulate pollutant concentration increased first and then decreased. (3) Sewage discharge pollution loads increased significantly with the increase of rainfall. Under the same rainfall conditions， pollution loads during the rain before the peak were much greater than which during the rain after the peak. (4)Influenced by the rain type and pre-evacuation of station， first flush effect of SS was not significant in light rain， moderate rain or heavy rain， but that of COD and TP was significant， which were mainly from the sewer sediment pollutant. First flush effect of dissolved pollutants was significant， which was not influenced by the rainfall and the rain type. (5) Strategies are proposed to reduce the pollutant load， including pipe network system with illicit connection reconstruction， pumping station optimization， intercepting capacity improvement and pipe network system dredging and maintenance， etc.