Bioretention systems have the potential for managing stormwater by reducing peak runoff flow and improving both surface and ground water quality in a natural and aesthetically pleasing manner. We tested unique iron-silica hybrid materials as amendment to two common soil bioretention base media; (1) sand and (2) sand-soil-compost (SSC) mix to develop and evaluate new filter media that improve hydraulic performance and pollutant removal efficiency. The hybrid materials contain nano-scale iron embedded in silica-based materials forming fine-grained, glass-like powder. The materials have been shown to have a tremendous ability to physico-chemically absorb and degrade pollutants such as oils, nutrients, and herbicides, which are commonly detected in stormwater runoff. At column scale, hydraulic performance and pollutant removal efficiency of different contents (0-2%) of iron-silica hybrid materials in two base soil media were evaluated. Simulated runoff events were applied seven times with spiked concentrations of runoff pollutants (i.e. nitrate, phosphate, motor oils, and atrazine) at a 7-day interval. Hydraulic performance of all the tested media was consistent over the simulated runoff events, exceeding a minimum infiltration rate (5.0 cm/h) required for bioretention systems. Removal efficiency of nutrients (~95%) and atrazine (~99%) was significantly improved with iron-silica material amendment compared to the control base media (~50% for nutrient and ~60% for atrazine). This is most likely due to increased absorption and reductive transformation capacities created by the iron-silica hybrid materials. Both base media showed excellent removal efficiency of motor oils (~99%) in a short term regardless of the addition of iron-silica hybrid materials. The hydraulic performance and pollutant removal efficiency of iron-silica hybrid materials to SSC mix is being evaluated at two field-scale bioretention systems constructed at the campus of College of Wooster (OH) to treat parking lot runoff. The presentation will include a discussion of the results from the field scale evaluation.
