An Evaluation of the Urban Storm Water Runoff Pollutant Removal Efficiency with a Focus on the Retention Time

Abstract

In urban areas, during heavy rain events various pollutants are flushed off impervious surfaces with storm water runoff and through the storm water drainage system directly discharged to surface water bodies. Commonly, storm water runoff sedimentation tanks are used to remove suspended solids and total petroleum hydrocarbons from the first portions of storm water runoff. Unfortunately, the operation of especially storm water sedimentation tanks is still quite complicated and not very effective. The regulation of outflow rate can be one of the ways to increase the effectiveness of pollutants removal using sedimentation tank technology. The research was performed at the storm water runoff treatment unit based on the sedimentation process. The aim of the study was to investigate the removal of suspended solids (SS) and total petroleum hydrocarbons (TPH) at the storm water runoff sedimentation tank with a focus on the retention time. Initially, the distribution of concentration of SS and TPH in various places of sedimentation tank after the rain event was investigated. The obtained results showed that the concentrations of SS and TPH are very similar all over the tank after a rain event. Therefore, it is more reasonable to take one composite sample instead several grab samples during the research of sedimentation process efficiency. According to the obtained SS and TPH removal efficiency results it was determined that optimal storm water runoff retention time in the researched sedimentation tank is 48 hour, when the inflow and outflow of sedimentation tank are closed.