Reduction of Pollutant Concentrations in Urban Stormwater Runoff by Settling

The pollutant removal efficiencies of stormwater runoff by settling were analyzed using field samples collected in 4 different raining events in a test bed installed in the Gwanpyung-Cheon stream in Daejeon.A 1.8 m high with 30 cm diameter cylindrical settling device was used for the settling test by measuring concentration of TSS, TP and TN for time and height.The pollutants removal rate was relatively high in the first 4 hours while 24 hours seem to be necessary to reach steady state in pollutant concentrations.However, there were no considerable differences in concentrations for height at a given time.This indicates most of particulate pollutant in the test seems to show independent settling with no interference to each other.Much part of particle sizes were distributed in the range of 10~100 µm.Average particulate fractions of TP and TN were estimated as 52.4% and 23.5%, respectively.This results explain why TN is difficult to remove by simple settling.This study indicates that a simple settling can provide effective method to remove significant amount of TSS and TP effectively and this can be used to protect urban river water quality.