Stormwater Phosphorus Removal Using an Innovative Filtration Media

Stormwater phosphorus (P) removal has received growing regulations in the last two decades. A regulatory guideline of 50–65% total phosphorus (TP) removal has been commonly implemented. However, many past BMP studies showed that it was difficult to consistently achieve TP removal rates in excess of 40%. Numerous treatment practices, even though sporadically achieving high initial TP removal rates, continued to release TP into effluent afterwards. To achieve successful implementation, characteristics of filtration media such as adsorption capacity, gradation, surface area, durability, toxicity, cost, environmentally friendly manufacturing process, easiness of maintenance, and convenience of disposal are all critical parameters. To develop a media that meets these requirements, hundreds of formulations were evaluated. The end result is an adsorptive light weight engineered media (EM). It is designed to efficiently remove TP from stormwater by adsorption of dissolved P and filtration of particulate P simultaneously. Bench scale evaluation results using simulated stormwater demonstrated 50% removal of 0.5 mg/L dissolve P solution for the first 1000 empty bed volumes (EBVs) when operating at 260 cm/hr. By comparison, zeolite commonly employed in stormwater treatment could only treat few dozens of EBVs under the same conditions before exhausted. In the subsequent field trials using real stormwater runoff, over 70% of influent TP was removed for two events with event mean concentrations (EMCs) of influent TP higher than 0.075 mg/L. In another event, influent TP was non-detectable (< 0.02 mg/L) and so did the effluent TP. No release of TP from the used media indicated the strong affinity sites provided by the adsorptive EM. More field scale testing is ongoing. In brief, all the available results show that EM promises to efficiently remove stormwater phosphorus.