Royal Environmental Systems, Inc.

Passive Filter – Sustainable BMP For Permanent Stormwater Treatment Of Heavy Metals, Nutrients, Hydrocarbons And Sediment


Passive filtration provides a sustainable alternative to classical drainage concepts for source control of hydrocarbons, heavy metals and nutrients that endanger our water bodies.

In urban areas with high building density, traditional drainage concepts like wetlands are not available and the concept of decentralized treatment facilities that can be housed in catch basin structures are a viable option for treatment of pollutants.

A European and US study is underway to determine the parameters of sustainable on-site retention and infiltration. The European study progressed in three stages. In the first stage the catch basin (hydrodynamic separator and filter housing) was developed and investigated on a laboratory scale, including the hydraulic behavior and the retention of the sediments. Secondly, filters of concrete were assessed in laboratory scale catch basins. The filters were charged with an artificial runoff, which was spiked with pollutants. Concentrations in the influent and the effluent were measured and the design details of the catch basin and its concrete filters were optimized. In the third step field investigations of the catch basin treatment facility were carried out to show the performance of the system while under real conditions.

The results of this sustainable alternative in European data showed, depending on the water runoff characteristics, more than 90% total suspended solids removal, between 40% and 95% reduction in heavy metals (zinc, cadmium, copper and lead), greater than 90% removal of mineral oils and more than 60% reduction in phosphorous.

In a cooperative effort, the U.S. study has been commissioned for the Ramsey-Washington Metro Watershed District (RWMWD) in Twin Cities, MN with the support of the Ramsey County Public Works, Hydro International, Royal Environmental, Water Tectonics and Barr Engineering will design, construct, study, and document the effectiveness of four different proprietary BMP configurations as treatment practices for addressing non-point source pollution. The results of this project will be used to determine the efficacy and potential for widespread application throughout the upper Midwest. In addition, performance data required in Washington State has been conducted by Water Tectonics and has shown similar removal rates to the European data.

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