Evaluation of an enhanced treatment media and permeable pavement base to remove stormwater nitrogen, phosphorus, and metals under simulated rainfall.

An enhanced stormwater treatment media, developed previously by the authors, was shown to effectively retain dissolved phosphorus (DP) and total Cu and Zn under simulated rainfall. The media comprises expanded shale aggregate, aluminum-based water treatment residual (WTR), and a psyllium-based binder. A 5-cm layer of media was installed as a permeable pavement base layer in a laboratory mesocosm and subjected to rainfall simulations using synthetic stormwater. At rainfall intensity of 0.66 cm/h, effluent DP event mean concentration (EMC) fell from an average of 0.22 mg/L P to below the EPA water quality criterion of 0.037 mg/L in 8 of 9 storms. DP retention increased at lower rainfall intensity and lower pH. Effluent EMC was lowered to less than 30 µg/L for total Cu and less than 92 µg/L for total Zn, on average, relative to average influent EMCs above 61 and 255 µg/L for total Cu and Zn, respectively. Effluent total Al EMCs were below the 25 µg/L detection limit for all storm simulations, indicating Al leaching from the WTR-containing media not to be an issue. Inclusion of an internal water storage (IWS) zone resulted in a 33% total nitrogen (TN) load reduction when adequate carbon was present to advance denitrification. This study provides an evaluation and demonstrates expected treatment performance of a novel stormwater treatment media under conditions representative of urban stormwater.