Effectiveness of Settling Treatment System to Reduce Urban Nonpoint Source Pollutant Load by First Flush

The effectiveness of the first flush treatment system using settling process was evaluated to reduce urban nonpoint source pollutant loads to surface water during storm events.A pilot scale system was constructed and tested in the field and surface runoff samples were collected automatically according to pre-defined conditions.Nine rainfall events were tested and average removal efficiencies of TSS (Total Suspended Solid), TP (Total Phosphorus) and TN (Total Nitrogen) were evaluated as 87.4%, 75.3%, and 43.6%, respectively.Concentration and removal efficiency of pollutants were found to be affected by an amount of rainfall and rainfall intensities of the respective events.This seemed to be caused by the greater particulate fractions of first flushed samples than the samples collected in later time periods during the same rainfall events.The study showed that it is possible to remove a significant portion of the nonpoint source pollutant loads in initial rainfall runoff by using a simple settling process for TSS and TP without requiring additional power or chemicals.