Low-Cost Filtration System to Treat First-Flush Stormwater

The aim of this paper is to evaluate the performance of the low-flow filtration system (LFFS) that Kogarah Municipal Council developed for treating and reusing the highly polluted first-flush stormwater (FFSW) while allowing the cleaner subsequent major stormwater flows to be directed to the major street drainage. The LFFS was evaluated through laboratory investigations using columns packed with different filter media to test the removal efficiency of pollutants such as zinc (Zn), total phosphorus (TP), total nitrogen (TN), total organic content, total petroleum hydrocarbons (TPH), and turbidity. The findings from this study demonstrate the effectiveness of the LFFS to largely reduce turbidity, TPH, and trace metals from the FFSW. The LFFS also partially removes dissolved organics, TP and TN. These pollutants are more commonly and effectively removed in subsequent processes of a stormwater treatment train. Further this paper highlights the importance of regular maintenance of the LFFS especially as it is only associated in removing the high pollutant loads during a storm event. Due to this first flush, a thick oily crust-formed layer requires monthly removal, and an entire replacement of the exhausted filter media is required quarterly. However considering the labor required to service the crust formed layer within the LFFS, it is more cost effective to replace the entire depth of filter media monthly.