Biofilters are rain gardens with underdrains that treat stormwater runoff from urban landscapes, especially where infiltration into shallow groundwater is infeasible or a concern. The biofilter media (e.g., sand, compost, peat, biochar), however, can release phosphate or limit plant growth, so stormwater professionals struggle to choose which media to use in biofilters. A four-year outdoor research study evaluated thirteen different mixes of eight different media components to determine benefits and consequences of using common and new innovative media components in biofiltration media. This presentation will share the final performance results including phosphate release or capture, plant growth, filtration rate, impacts from road salt addition on phosphate release, and simple tests and metrics that could be used to determine which components have potential to release phosphate. The final recommendations from this project are intended to guide stormwater practitioners towards better designed biofiltration practices that capture phosphorus and support healthy vegetation.

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